ssl
Bill Janssen <bill.janssen@gmail.com>
Bill Janssen <bill.janssen@gmail.com>
Source code: Lib/ssl.py
single: OpenSSL; (use in module ssl)
TLS, SSL, Transport Layer Security, Secure Sockets Layer
This module provides access to Transport Layer Security (often known as "Secure Sockets Layer") encryption and peer authentication facilities for network sockets, both client-side and server-side. This module uses the OpenSSL library. It is available on all modern Unix systems, Windows, Mac OS X, and probably additional platforms, as long as OpenSSL is installed on that platform.
Note
Some behavior may be platform dependent, since calls are made to the operating system socket APIs. The installed version of OpenSSL may also cause variations in behavior. For example, TLSv1.3 with OpenSSL version 1.1.1.
Warning
Don't use this module without reading the ssl-security
. Doing so may lead to a false sense of security, as the default settings of the ssl module are not necessarily appropriate for your application.
This section documents the objects and functions in the ssl
module; for more general information about TLS, SSL, and certificates, the reader is referred to the documents in the "See Also" section at the bottom.
This module provides a class, ssl.SSLSocket
, which is derived from the socket.socket
type, and provides a socket-like wrapper that also encrypts and decrypts the data going over the socket with SSL. It supports additional methods such as getpeercert
, which retrieves the certificate of the other side of the connection, and cipher
, which retrieves the cipher being used for the secure connection.
For more sophisticated applications, the ssl.SSLContext
class helps manage settings and certificates, which can then be inherited by SSL sockets created through the SSLContext.wrap_socket
method.
3.5.3 Updated to support linking with OpenSSL 1.1.0
3.6
OpenSSL 0.9.8, 1.0.0 and 1.0.1 are deprecated and no longer supported. In the future the ssl module will require at least OpenSSL 1.0.2 or 1.1.0.
3.10
644
has been implemented. The ssl module requires OpenSSL 1.1.1 or newer.
Use of deprecated constants and functions result in deprecation warnings.
Since Python 3.2 and 2.7.9, it is recommended to use the SSLContext.wrap_socket
of an SSLContext
instance to wrap sockets as SSLSocket
objects. The helper functions create_default_context
returns a new context with secure default settings. The old wrap_socket
function is deprecated since it is both inefficient and has no support for server name indication (SNI) and hostname matching.
Client socket example with default context and IPv4/IPv6 dual stack:
import socket
import ssl
hostname = 'www.python.org'
context = ssl.create_default_context()
with socket.create_connection((hostname, 443)) as sock:
with context.wrap_socket(sock, server_hostname=hostname) as ssock:
print(ssock.version())
Client socket example with custom context and IPv4:
hostname = 'www.python.org'
# PROTOCOL_TLS_CLIENT requires valid cert chain and hostname
context = ssl.SSLContext(ssl.PROTOCOL_TLS_CLIENT)
context.load_verify_locations('path/to/cabundle.pem')
with socket.socket(socket.AF_INET, socket.SOCK_STREAM, 0) as sock:
with context.wrap_socket(sock, server_hostname=hostname) as ssock:
print(ssock.version())
Server socket example listening on localhost IPv4:
context = ssl.SSLContext(ssl.PROTOCOL_TLS_SERVER)
context.load_cert_chain('/path/to/certchain.pem', '/path/to/private.key')
with socket.socket(socket.AF_INET, socket.SOCK_STREAM, 0) as sock:
sock.bind(('127.0.0.1', 8443))
sock.listen(5)
with context.wrap_socket(sock, server_side=True) as ssock:
conn, addr = ssock.accept()
...
A convenience function helps create SSLContext
objects for common purposes.
create_default_context(purpose=Purpose.SERVER_AUTH, cafile=None, capath=None, cadata=None)
Return a new SSLContext
object with default settings for the given purpose. The settings are chosen by the ssl
module, and usually represent a higher security level than when calling the SSLContext
constructor directly.
cafile, capath, cadata represent optional CA certificates to trust for certificate verification, as in SSLContext.load_verify_locations
. If all three are None
, this function can choose to trust the system's default CA certificates instead.
The settings are: PROTOCOL_TLS_CLIENT
or PROTOCOL_TLS_SERVER
, OP_NO_SSLv2
, and OP_NO_SSLv3
with high encryption cipher suites without RC4 and without unauthenticated cipher suites. Passing ~Purpose.SERVER_AUTH
as purpose sets ~SSLContext.verify_mode
to CERT_REQUIRED
and either loads CA certificates (when at least one of cafile, capath or cadata is given) or uses SSLContext.load_default_certs
to load default CA certificates.
When ~SSLContext.keylog_filename
is supported and the environment variable SSLKEYLOGFILE
is set, create_default_context
enables key logging.
Note
The protocol, options, cipher and other settings may change to more restrictive values anytime without prior deprecation. The values represent a fair balance between compatibility and security.
If your application needs specific settings, you should create a SSLContext
and apply the settings yourself.
Note
If you find that when certain older clients or servers attempt to connect with a SSLContext
created by this function that they get an error stating "Protocol or cipher suite mismatch", it may be that they only support SSL3.0 which this function excludes using the OP_NO_SSLv3
. SSL3.0 is widely considered to be completely broken. If you still wish to continue to use this function but still allow SSL 3.0 connections you can re-enable them using:
ctx = ssl.create_default_context(Purpose.CLIENT_AUTH) ctx.options &= ~ssl.OP_NO_SSLv3
3.4
3.4.4
RC4 was dropped from the default cipher string.
3.6
ChaCha20/Poly1305 was added to the default cipher string.
3DES was dropped from the default cipher string.
3.8
Support for key logging to SSLKEYLOGFILE
was added.
3.10
The context now uses PROTOCOL_TLS_CLIENT
or PROTOCOL_TLS_SERVER
protocol instead of generic PROTOCOL_TLS
.
SSLError
Raised to signal an error from the underlying SSL implementation (currently provided by the OpenSSL library). This signifies some problem in the higher-level encryption and authentication layer that's superimposed on the underlying network connection. This error is a subtype of OSError
. The error code and message of SSLError
instances are provided by the OpenSSL library.
3.3 SSLError
used to be a subtype of socket.error
.
library
A string mnemonic designating the OpenSSL submodule in which the error occurred, such as SSL
, PEM
or X509
. The range of possible values depends on the OpenSSL version.
3.3
reason
A string mnemonic designating the reason this error occurred, for example CERTIFICATE_VERIFY_FAILED
. The range of possible values depends on the OpenSSL version.
3.3
SSLZeroReturnError
A subclass of SSLError
raised when trying to read or write and the SSL connection has been closed cleanly. Note that this doesn't mean that the underlying transport (read TCP) has been closed.
3.3
SSLWantReadError
A subclass of SSLError
raised by a non-blocking SSL socket
<ssl-nonblocking>
when trying to read or write data, but more data needs to be received on the underlying TCP transport before the request can be fulfilled.
3.3
SSLWantWriteError
A subclass of SSLError
raised by a non-blocking SSL socket
<ssl-nonblocking>
when trying to read or write data, but more data needs to be sent on the underlying TCP transport before the request can be fulfilled.
3.3
SSLSyscallError
A subclass of SSLError
raised when a system error was encountered while trying to fulfill an operation on a SSL socket. Unfortunately, there is no easy way to inspect the original errno number.
3.3
SSLEOFError
A subclass of SSLError
raised when the SSL connection has been terminated abruptly. Generally, you shouldn't try to reuse the underlying transport when this error is encountered.
3.3
SSLCertVerificationError
A subclass of SSLError
raised when certificate validation has failed.
3.7
verify_code
A numeric error number that denotes the verification error.
verify_message
A human readable string of the verification error.
CertificateError
An alias for SSLCertVerificationError
.
3.7 The exception is now an alias for SSLCertVerificationError
.
RAND_bytes(num)
Return num cryptographically strong pseudo-random bytes. Raises an SSLError
if the PRNG has not been seeded with enough data or if the operation is not supported by the current RAND method. RAND_status
can be used to check the status of the PRNG and RAND_add
can be used to seed the PRNG.
For almost all applications os.urandom
is preferable.
Read the Wikipedia article, Cryptographically secure pseudorandom number generator (CSPRNG), to get the requirements of a cryptographically strong generator.
3.3
RAND_pseudo_bytes(num)
Return (bytes, is_cryptographic): bytes are num pseudo-random bytes, is_cryptographic is True
if the bytes generated are cryptographically strong. Raises an SSLError
if the operation is not supported by the current RAND method.
Generated pseudo-random byte sequences will be unique if they are of sufficient length, but are not necessarily unpredictable. They can be used for non-cryptographic purposes and for certain purposes in cryptographic protocols, but usually not for key generation etc.
For almost all applications os.urandom
is preferable.
3.3
3.6
OpenSSL has deprecated ssl.RAND_pseudo_bytes
, use ssl.RAND_bytes
instead.
RAND_status()
Return True
if the SSL pseudo-random number generator has been seeded with 'enough' randomness, and False
otherwise. You can use ssl.RAND_egd
and ssl.RAND_add
to increase the randomness of the pseudo-random number generator.
RAND_add(bytes, entropy)
Mix the given bytes into the SSL pseudo-random number generator. The parameter entropy (a float) is a lower bound on the entropy contained in string (so you can always use 0.0
). See 1750
for more information on sources of entropy.
3.5 Writable bytes-like object
is now accepted.
import ssl
match_hostname(cert, hostname)
Verify that cert (in decoded format as returned by SSLSocket.getpeercert
) matches the given hostname. The rules applied are those for checking the identity of HTTPS servers as outlined in 2818
, 5280
and 6125
. In addition to HTTPS, this function should be suitable for checking the identity of servers in various SSL-based protocols such as FTPS, IMAPS, POPS and others.
CertificateError
is raised on failure. On success, the function returns nothing:
>>> cert = {'subject': ((('commonName', 'example.com'),),)}
>>> ssl.match_hostname(cert, "example.com")
>>> ssl.match_hostname(cert, "example.org")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/home/py3k/Lib/ssl.py", line 130, in match_hostname
ssl.CertificateError: hostname 'example.org' doesn't match 'example.com'
3.2
3.3.3 The function now follows 6125
, section 6.4.3 and does neither match multiple wildcards (e.g. *.*.com
or *a*.example.org
) nor a wildcard inside an internationalized domain names (IDN) fragment. IDN A-labels such as www*.xn--pthon-kva.org
are still supported, but x*.python.org
no longer matches xn--tda.python.org
.
3.5 Matching of IP addresses, when present in the subjectAltName field of the certificate, is now supported.
3.7 The function is no longer used to TLS connections. Hostname matching is now performed by OpenSSL.
Allow wildcard when it is the leftmost and the only character in that segment. Partial wildcards like www*.example.com
are no longer supported.
3.7
cert_time_to_seconds(cert_time)
Return the time in seconds since the Epoch, given the cert_time
string representing the "notBefore" or "notAfter" date from a certificate in "%b %d %H:%M:%S %Y %Z"
strptime format (C locale).
Here's an example:
newcontext
>>> import ssl >>> timestamp = ssl.cert_time_to_seconds("Jan 5 09:34:43 2018 GMT") >>> timestamp # doctest: +SKIP 1515144883 >>> from datetime import datetime >>> print(datetime.utcfromtimestamp(timestamp)) # doctest: +SKIP 2018-01-05 09:34:43
"notBefore" or "notAfter" dates must use GMT (5280
).
3.5 Interpret the input time as a time in UTC as specified by 'GMT' timezone in the input string. Local timezone was used previously. Return an integer (no fractions of a second in the input format)
get_server_certificate(addr, ssl_version=PROTOCOL_TLS_CLIENT, ca_certs=None[, timeout])
Given the address addr
of an SSL-protected server, as a (hostname, port-number) pair, fetches the server's certificate, and returns it as a PEM-encoded string. If ssl_version
is specified, uses that version of the SSL protocol to attempt to connect to the server. If ca_certs
is specified, it should be a file containing a list of root certificates, the same format as used for the same parameter in SSLContext.wrap_socket
. The call will attempt to validate the server certificate against that set of root certificates, and will fail if the validation attempt fails. A timeout can be specified with the timeout
parameter.
3.3 This function is now IPv6-compatible.
3.5 The default ssl_version is changed from PROTOCOL_SSLv3
to PROTOCOL_TLS
for maximum compatibility with modern servers.
3.10 The timeout parameter was added.
DER_cert_to_PEM_cert(DER_cert_bytes)
Given a certificate as a DER-encoded blob of bytes, returns a PEM-encoded string version of the same certificate.
PEM_cert_to_DER_cert(PEM_cert_string)
Given a certificate as an ASCII PEM string, returns a DER-encoded sequence of bytes for that same certificate.
get_default_verify_paths()
Returns a named tuple with paths to OpenSSL's default cafile and capath. The paths are the same as used by SSLContext.set_default_verify_paths
. The return value is a named tuple
DefaultVerifyPaths
:
cafile
- resolved path to cafile orNone
if the file doesn't exist,capath
- resolved path to capath orNone
if the directory doesn't exist,openssl_cafile_env
- OpenSSL's environment key that points to a cafile,openssl_cafile
- hard coded path to a cafile,openssl_capath_env
- OpenSSL's environment key that points to a capath,openssl_capath
- hard coded path to a capath directory
LibreSSL ignores the environment vars openssl_cafile_env
and openssl_capath_env
.
3.4
enum_certificates(store_name)
Retrieve certificates from Windows' system cert store. store_name may be one of CA
, ROOT
or MY
. Windows may provide additional cert stores, too.
The function returns a list of (cert_bytes, encoding_type, trust) tuples. The encoding_type specifies the encoding of cert_bytes. It is either x509_asn
for X.509 ASN.1 data or pkcs_7_asn
for PKCS#7 ASN.1 data. Trust specifies the purpose of the certificate as a set of OIDS or exactly True
if the certificate is trustworthy for all purposes.
Example:
>>> ssl.enum_certificates("CA")
[(b'data...', 'x509_asn', {'1.3.6.1.5.5.7.3.1', '1.3.6.1.5.5.7.3.2'}),
(b'data...', 'x509_asn', True)]
Windows.
3.4
enum_crls(store_name)
Retrieve CRLs from Windows' system cert store. store_name may be one of CA
, ROOT
or MY
. Windows may provide additional cert stores, too.
The function returns a list of (cert_bytes, encoding_type, trust) tuples. The encoding_type specifies the encoding of cert_bytes. It is either x509_asn
for X.509 ASN.1 data or pkcs_7_asn
for PKCS#7 ASN.1 data.
Windows.
3.4
wrap_socket(sock, keyfile=None, certfile=None, server_side=False, cert_reqs=CERT_NONE, ssl_version=PROTOCOL_TLS, ca_certs=None, do_handshake_on_connect=True, suppress_ragged_eofs=True, ciphers=None)
Takes an instance sock
of socket.socket
, and returns an instance of ssl.SSLSocket
, a subtype of socket.socket
, which wraps the underlying socket in an SSL context. sock
must be a ~socket.SOCK_STREAM
socket; other socket types are unsupported.
Internally, function creates a SSLContext
with protocol ssl_version and SSLContext.options
set to cert_reqs. If parameters keyfile, certfile, ca_certs or ciphers are set, then the values are passed to SSLContext.load_cert_chain
, SSLContext.load_verify_locations
, and SSLContext.set_ciphers
.
The arguments server_side, do_handshake_on_connect, and suppress_ragged_eofs have the same meaning as SSLContext.wrap_socket
.
3.7
Since Python 3.2 and 2.7.9, it is recommended to use the SSLContext.wrap_socket
instead of wrap_socket
. The top-level function is limited and creates an insecure client socket without server name indication or hostname matching.
All constants are now
enum.IntEnum
orenum.IntFlag
collections.3.6
CERT_NONE
Possible value for SSLContext.verify_mode
, or the cert_reqs
parameter to wrap_socket
. Except for PROTOCOL_TLS_CLIENT
, it is the default mode. With client-side sockets, just about any cert is accepted. Validation errors, such as untrusted or expired cert, are ignored and do not abort the TLS/SSL handshake.
In server mode, no certificate is requested from the client, so the client does not send any for client cert authentication.
See the discussion of ssl-security
below.
CERT_OPTIONAL
Possible value for SSLContext.verify_mode
, or the cert_reqs
parameter to wrap_socket
. In client mode, CERT_OPTIONAL
has the same meaning as CERT_REQUIRED
. It is recommended to use CERT_REQUIRED
for client-side sockets instead.
In server mode, a client certificate request is sent to the client. The client may either ignore the request or send a certificate in order perform TLS client cert authentication. If the client chooses to send a certificate, it is verified. Any verification error immediately aborts the TLS handshake.
Use of this setting requires a valid set of CA certificates to be passed, either to SSLContext.load_verify_locations
or as a value of the ca_certs
parameter to wrap_socket
.
CERT_REQUIRED
Possible value for SSLContext.verify_mode
, or the cert_reqs
parameter to wrap_socket
. In this mode, certificates are required from the other side of the socket connection; an SSLError
will be raised if no certificate is provided, or if its validation fails. This mode is not sufficient to verify a certificate in client mode as it does not match hostnames. ~SSLContext.check_hostname
must be enabled as well to verify the authenticity of a cert. PROTOCOL_TLS_CLIENT
uses CERT_REQUIRED
and enables ~SSLContext.check_hostname
by default.
With server socket, this mode provides mandatory TLS client cert authentication. A client certificate request is sent to the client and the client must provide a valid and trusted certificate.
Use of this setting requires a valid set of CA certificates to be passed, either to SSLContext.load_verify_locations
or as a value of the ca_certs
parameter to wrap_socket
.
enum.IntEnum
collection of CERT* constants.
3.6
VERIFY_DEFAULT
Possible value for SSLContext.verify_flags
. In this mode, certificate revocation lists (CRLs) are not checked. By default OpenSSL does neither require nor verify CRLs.
3.4
VERIFY_CRL_CHECK_LEAF
Possible value for SSLContext.verify_flags
. In this mode, only the peer cert is checked but none of the intermediate CA certificates. The mode requires a valid CRL that is signed by the peer cert's issuer (its direct ancestor CA). If no proper CRL has been loaded with SSLContext.load_verify_locations
, validation will fail.
3.4
VERIFY_CRL_CHECK_CHAIN
Possible value for SSLContext.verify_flags
. In this mode, CRLs of all certificates in the peer cert chain are checked.
3.4
VERIFY_X509_STRICT
Possible value for SSLContext.verify_flags
to disable workarounds for broken X.509 certificates.
3.4
VERIFY_ALLOW_PROXY_CERTS
Possible value for SSLContext.verify_flags
to enables proxy certificate verification.
3.10
VERIFY_X509_TRUSTED_FIRST
Possible value for SSLContext.verify_flags
. It instructs OpenSSL to prefer trusted certificates when building the trust chain to validate a certificate. This flag is enabled by default.
3.4.4
VERIFY_X509_PARTIAL_CHAIN
Possible value for SSLContext.verify_flags
. It instructs OpenSSL to accept intermediate CAs in the trust store to be treated as trust-anchors, in the same way as the self-signed root CA certificates. This makes it possible to trust certificates issued by an intermediate CA without having to trust its ancestor root CA.
3.10
enum.IntFlag
collection of VERIFY* constants.
3.6
PROTOCOL_TLS
Selects the highest protocol version that both the client and server support. Despite the name, this option can select both "SSL" and "TLS" protocols.
3.6
3.10
Use PROTOCOL_TLS_CLIENT
or PROTOCOL_TLS_SERVER
instead.
PROTOCOL_TLS_CLIENT
Auto-negotiate the highest protocol version like PROTOCOL_TLS
, but only support client-side SSLSocket
connections. The protocol enables CERT_REQUIRED
and ~SSLContext.check_hostname
by default.
3.6
PROTOCOL_TLS_SERVER
Auto-negotiate the highest protocol version like PROTOCOL_TLS
, but only support server-side SSLSocket
connections.
3.6
PROTOCOL_SSLv23
Alias for PROTOCOL_TLS
.
3.6
Use PROTOCOL_TLS
instead.
PROTOCOL_SSLv2
Selects SSL version 2 as the channel encryption protocol.
This protocol is not available if OpenSSL is compiled with the OPENSSL_NO_SSL2
flag.
Warning
SSL version 2 is insecure. Its use is highly discouraged.
3.6
OpenSSL has removed support for SSLv2.
PROTOCOL_SSLv3
Selects SSL version 3 as the channel encryption protocol.
This protocol is not be available if OpenSSL is compiled with the OPENSSL_NO_SSLv3
flag.
Warning
SSL version 3 is insecure. Its use is highly discouraged.
3.6
OpenSSL has deprecated all version specific protocols. Use the default protocol PROTOCOL_TLS_SERVER
or PROTOCOL_TLS_CLIENT
with SSLContext.minimum_version
and SSLContext.maximum_version
instead.
PROTOCOL_TLSv1
Selects TLS version 1.0 as the channel encryption protocol.
3.6
OpenSSL has deprecated all version specific protocols.
PROTOCOL_TLSv1_1
Selects TLS version 1.1 as the channel encryption protocol. Available only with openssl version 1.0.1+.
3.4
3.6
OpenSSL has deprecated all version specific protocols.
PROTOCOL_TLSv1_2
Selects TLS version 1.2 as the channel encryption protocol. Available only with openssl version 1.0.1+.
3.4
3.6
OpenSSL has deprecated all version specific protocols.
OP_ALL
Enables workarounds for various bugs present in other SSL implementations. This option is set by default. It does not necessarily set the same flags as OpenSSL's SSL_OP_ALL
constant.
3.2
OP_NO_SSLv2
Prevents an SSLv2 connection. This option is only applicable in conjunction with PROTOCOL_TLS
. It prevents the peers from choosing SSLv2 as the protocol version.
3.2
3.6
SSLv2 is deprecated
OP_NO_SSLv3
Prevents an SSLv3 connection. This option is only applicable in conjunction with PROTOCOL_TLS
. It prevents the peers from choosing SSLv3 as the protocol version.
3.2
3.6
SSLv3 is deprecated
OP_NO_TLSv1
Prevents a TLSv1 connection. This option is only applicable in conjunction with PROTOCOL_TLS
. It prevents the peers from choosing TLSv1 as the protocol version.
3.2
3.7 The option is deprecated since OpenSSL 1.1.0, use the new SSLContext.minimum_version
and SSLContext.maximum_version
instead.
OP_NO_TLSv1_1
Prevents a TLSv1.1 connection. This option is only applicable in conjunction with PROTOCOL_TLS
. It prevents the peers from choosing TLSv1.1 as the protocol version. Available only with openssl version 1.0.1+.
3.4
3.7 The option is deprecated since OpenSSL 1.1.0.
OP_NO_TLSv1_2
Prevents a TLSv1.2 connection. This option is only applicable in conjunction with PROTOCOL_TLS
. It prevents the peers from choosing TLSv1.2 as the protocol version. Available only with openssl version 1.0.1+.
3.4
3.7 The option is deprecated since OpenSSL 1.1.0.
OP_NO_TLSv1_3
Prevents a TLSv1.3 connection. This option is only applicable in conjunction with PROTOCOL_TLS
. It prevents the peers from choosing TLSv1.3 as the protocol version. TLS 1.3 is available with OpenSSL 1.1.1 or later. When Python has been compiled against an older version of OpenSSL, the flag defaults to 0.
3.7
3.7 The option is deprecated since OpenSSL 1.1.0. It was added to 2.7.15, 3.6.3 and 3.7.0 for backwards compatibility with OpenSSL 1.0.2.
OP_NO_RENEGOTIATION
Disable all renegotiation in TLSv1.2 and earlier. Do not send HelloRequest messages, and ignore renegotiation requests via ClientHello.
This option is only available with OpenSSL 1.1.0h and later.
3.7
OP_CIPHER_SERVER_PREFERENCE
Use the server's cipher ordering preference, rather than the client's. This option has no effect on client sockets and SSLv2 server sockets.
3.3
OP_SINGLE_DH_USE
Prevents re-use of the same DH key for distinct SSL sessions. This improves forward secrecy but requires more computational resources. This option only applies to server sockets.
3.3
OP_SINGLE_ECDH_USE
Prevents re-use of the same ECDH key for distinct SSL sessions. This improves forward secrecy but requires more computational resources. This option only applies to server sockets.
3.3
OP_ENABLE_MIDDLEBOX_COMPAT
Send dummy Change Cipher Spec (CCS) messages in TLS 1.3 handshake to make a TLS 1.3 connection look more like a TLS 1.2 connection.
This option is only available with OpenSSL 1.1.1 and later.
3.8
OP_NO_COMPRESSION
Disable compression on the SSL channel. This is useful if the application protocol supports its own compression scheme.
3.3
enum.IntFlag
collection of OP* constants.
OP_NO_TICKET
Prevent client side from requesting a session ticket.
3.6
OP_IGNORE_UNEXPECTED_EOF
Ignore unexpected shutdown of TLS connections.
This option is only available with OpenSSL 3.0.0 and later.
3.10
HAS_ALPN
Whether the OpenSSL library has built-in support for the Application-Layer Protocol Negotiation TLS extension as described in 7301
.
3.5
HAS_NEVER_CHECK_COMMON_NAME
Whether the OpenSSL library has built-in support not checking subject common name and SSLContext.hostname_checks_common_name
is writeable.
3.7
HAS_ECDH
Whether the OpenSSL library has built-in support for the Elliptic Curve-based Diffie-Hellman key exchange. This should be true unless the feature was explicitly disabled by the distributor.
3.3
HAS_SNI
Whether the OpenSSL library has built-in support for the Server Name Indication extension (as defined in 6066
).
3.2
HAS_NPN
Whether the OpenSSL library has built-in support for the Next Protocol Negotiation as described in the Application Layer Protocol Negotiation. When true, you can use the SSLContext.set_npn_protocols
method to advertise which protocols you want to support.
3.3
HAS_SSLv2
Whether the OpenSSL library has built-in support for the SSL 2.0 protocol.
3.7
HAS_SSLv3
Whether the OpenSSL library has built-in support for the SSL 3.0 protocol.
3.7
HAS_TLSv1
Whether the OpenSSL library has built-in support for the TLS 1.0 protocol.
3.7
HAS_TLSv1_1
Whether the OpenSSL library has built-in support for the TLS 1.1 protocol.
3.7
HAS_TLSv1_2
Whether the OpenSSL library has built-in support for the TLS 1.2 protocol.
3.7
HAS_TLSv1_3
Whether the OpenSSL library has built-in support for the TLS 1.3 protocol.
3.7
CHANNEL_BINDING_TYPES
List of supported TLS channel binding types. Strings in this list can be used as arguments to SSLSocket.get_channel_binding
.
3.3
OPENSSL_VERSION
The version string of the OpenSSL library loaded by the interpreter:
>>> ssl.OPENSSL_VERSION
'OpenSSL 1.0.2k 26 Jan 2017'
3.2
OPENSSL_VERSION_INFO
A tuple of five integers representing version information about the OpenSSL library:
>>> ssl.OPENSSL_VERSION_INFO
(1, 0, 2, 11, 15)
3.2
OPENSSL_VERSION_NUMBER
The raw version number of the OpenSSL library, as a single integer:
>>> ssl.OPENSSL_VERSION_NUMBER
268443839
>>> hex(ssl.OPENSSL_VERSION_NUMBER)
'0x100020bf'
3.2
ALERT_DESCRIPTION_HANDSHAKE_FAILURE ALERT_DESCRIPTION_INTERNAL_ERROR ALERT_DESCRIPTION*
Alert Descriptions from 5246
and others. The IANA TLS Alert Registry contains this list and references to the RFCs where their meaning is defined.
Used as the return value of the callback function in SSLContext.set_servername_callback
.
3.4
enum.IntEnum
collection of ALERT_DESCRIPTION* constants.
3.6
Purpose.SERVER_AUTH
Option for create_default_context
and SSLContext.load_default_certs
. This value indicates that the context may be used to authenticate Web servers (therefore, it will be used to create client-side sockets).
3.4
Purpose.CLIENT_AUTH
Option for create_default_context
and SSLContext.load_default_certs
. This value indicates that the context may be used to authenticate Web clients (therefore, it will be used to create server-side sockets).
3.4
enum.IntEnum
collection of SSL_ERROR* constants.
3.6
enum.IntEnum
collection of SSL and TLS versions for SSLContext.maximum_version
and SSLContext.minimum_version
.
3.7
TLSVersion.MINIMUM_SUPPORTED
TLSVersion.MAXIMUM_SUPPORTED
The minimum or maximum supported SSL or TLS version. These are magic constants. Their values don't reflect the lowest and highest available TLS/SSL versions.
TLSVersion.SSLv3
TLSVersion.TLSv1
TLSVersion.TLSv1_1
TLSVersion.TLSv1_2
TLSVersion.TLSv1_3
SSL 3.0 to TLS 1.3.
3.10
All TLSVersion
members except TLSVersion.TLSv1_2
and TLSVersion.TLSv1_3
are deprecated.
SSL sockets provide the following methods of socket-objects
:
~socket.socket.accept()
~socket.socket.bind()
~socket.socket.close()
~socket.socket.connect()
~socket.socket.detach()
~socket.socket.fileno()
~socket.socket.getpeername()
,~socket.socket.getsockname()
~socket.socket.getsockopt()
,~socket.socket.setsockopt()
~socket.socket.gettimeout()
,~socket.socket.settimeout()
,~socket.socket.setblocking()
~socket.socket.listen()
~socket.socket.makefile()
~socket.socket.recv()
,~socket.socket.recv_into()
(but passing a non-zeroflags
argument is not allowed)~socket.socket.send()
,~socket.socket.sendall()
(with the same limitation)~socket.socket.sendfile()
(butos.sendfile
will be used for plain-text sockets only, else~socket.socket.send()
will be used)~socket.socket.shutdown()
However, since the SSL (and TLS) protocol has its own framing atop of TCP, the SSL sockets abstraction can, in certain respects, diverge from the specification of normal, OS-level sockets. See especially the notes on non-blocking sockets <ssl-nonblocking>
.
Instances of SSLSocket
must be created using the SSLContext.wrap_socket
method.
3.5 The sendfile
method was added.
3.5 The shutdown
does not reset the socket timeout each time bytes are received or sent. The socket timeout is now to maximum total duration of the shutdown.
3.6 It is deprecated to create a SSLSocket
instance directly, use SSLContext.wrap_socket
to wrap a socket.
3.7 SSLSocket
instances must to created with ~SSLContext.wrap_socket
. In earlier versions, it was possible to create instances directly. This was never documented or officially supported.
3.10 Python now uses SSL_read_ex
and SSL_write_ex
internally. The functions support reading and writing of data larger than 2 GB. Writing zero-length data no longer fails with a protocol violation error.
SSL sockets also have the following additional methods and attributes:
SSLSocket.read(len=1024, buffer=None)
Read up to len bytes of data from the SSL socket and return the result as a bytes
instance. If buffer is specified, then read into the buffer instead, and return the number of bytes read.
Raise SSLWantReadError
or SSLWantWriteError
if the socket is non-blocking <ssl-nonblocking>
and the read would block.
As at any time a re-negotiation is possible, a call to read
can also cause write operations.
3.5 The socket timeout is no more reset each time bytes are received or sent. The socket timeout is now to maximum total duration to read up to len bytes.
3.6 Use ~SSLSocket.recv
instead of ~SSLSocket.read
.
SSLSocket.write(buf)
Write buf to the SSL socket and return the number of bytes written. The buf argument must be an object supporting the buffer interface.
Raise SSLWantReadError
or SSLWantWriteError
if the socket is non-blocking <ssl-nonblocking>
and the write would block.
As at any time a re-negotiation is possible, a call to write
can also cause read operations.
3.5 The socket timeout is no more reset each time bytes are received or sent. The socket timeout is now to maximum total duration to write buf.
3.6 Use ~SSLSocket.send
instead of ~SSLSocket.write
.
Note
The ~SSLSocket.read
and ~SSLSocket.write
methods are the low-level methods that read and write unencrypted, application-level data and decrypt/encrypt it to encrypted, wire-level data. These methods require an active SSL connection, i.e. the handshake was completed and SSLSocket.unwrap
was not called.
Normally you should use the socket API methods like ~socket.socket.recv
and ~socket.socket.send
instead of these methods.
SSLSocket.do_handshake()
Perform the SSL setup handshake.
3.4 The handshake method also performs match_hostname
when the ~SSLContext.check_hostname
attribute of the socket's ~SSLSocket.context
is true.
3.5 The socket timeout is no more reset each time bytes are received or sent. The socket timeout is now to maximum total duration of the handshake.
3.7 Hostname or IP address is matched by OpenSSL during handshake. The function match_hostname
is no longer used. In case OpenSSL refuses a hostname or IP address, the handshake is aborted early and a TLS alert message is send to the peer.
SSLSocket.getpeercert(binary_form=False)
If there is no certificate for the peer on the other end of the connection, return None
. If the SSL handshake hasn't been done yet, raise ValueError
.
If the binary_form
parameter is False
, and a certificate was received from the peer, this method returns a dict
instance. If the certificate was not validated, the dict is empty. If the certificate was validated, it returns a dict with several keys, amongst them subject
(the principal for which the certificate was issued) and issuer
(the principal issuing the certificate). If a certificate contains an instance of the Subject Alternative Name extension (see 3280
), there will also be a subjectAltName
key in the dictionary.
The subject
and issuer
fields are tuples containing the sequence of relative distinguished names (RDNs) given in the certificate's data structure for the respective fields, and each RDN is a sequence of name-value pairs. Here is a real-world example:
{'issuer': ((('countryName', 'IL'),),
(('organizationName', 'StartCom Ltd.'),),
(('organizationalUnitName',
'Secure Digital Certificate Signing'),),
(('commonName',
'StartCom Class 2 Primary Intermediate Server CA'),)),
'notAfter': 'Nov 22 08:15:19 2013 GMT',
'notBefore': 'Nov 21 03:09:52 2011 GMT',
'serialNumber': '95F0',
'subject': ((('description', '571208-SLe257oHY9fVQ07Z'),),
(('countryName', 'US'),),
(('stateOrProvinceName', 'California'),),
(('localityName', 'San Francisco'),),
(('organizationName', 'Electronic Frontier Foundation, Inc.'),),
(('commonName', '*.eff.org'),),
(('emailAddress', 'hostmaster@eff.org'),)),
'subjectAltName': (('DNS', '*.eff.org'), ('DNS', 'eff.org')),
'version': 3}
Note
To validate a certificate for a particular service, you can use the match_hostname
function.
If the binary_form
parameter is True
, and a certificate was provided, this method returns the DER-encoded form of the entire certificate as a sequence of bytes, or None
if the peer did not provide a certificate. Whether the peer provides a certificate depends on the SSL socket's role:
- for a client SSL socket, the server will always provide a certificate, regardless of whether validation was required;
- for a server SSL socket, the client will only provide a certificate when requested by the server; therefore
getpeercert
will returnNone
if you usedCERT_NONE
(rather thanCERT_OPTIONAL
orCERT_REQUIRED
).
3.2 The returned dictionary includes additional items such as issuer
and notBefore
.
3.4 ValueError
is raised when the handshake isn't done. The returned dictionary includes additional X509v3 extension items such as crlDistributionPoints
, caIssuers
and OCSP
URIs.
3.9 IPv6 address strings no longer have a trailing new line.
SSLSocket.cipher()
Returns a three-value tuple containing the name of the cipher being used, the version of the SSL protocol that defines its use, and the number of secret bits being used. If no connection has been established, returns None
.
SSLSocket.shared_ciphers()
Return the list of ciphers shared by the client during the handshake. Each entry of the returned list is a three-value tuple containing the name of the cipher, the version of the SSL protocol that defines its use, and the number of secret bits the cipher uses. ~SSLSocket.shared_ciphers
returns None
if no connection has been established or the socket is a client socket.
3.5
SSLSocket.compression()
Return the compression algorithm being used as a string, or None
if the connection isn't compressed.
If the higher-level protocol supports its own compression mechanism, you can use OP_NO_COMPRESSION
to disable SSL-level compression.
3.3
SSLSocket.get_channel_binding(cb_type="tls-unique")
Get channel binding data for current connection, as a bytes object. Returns None
if not connected or the handshake has not been completed.
The cb_type parameter allow selection of the desired channel binding type. Valid channel binding types are listed in the CHANNEL_BINDING_TYPES
list. Currently only the 'tls-unique' channel binding, defined by 5929
, is supported. ValueError
will be raised if an unsupported channel binding type is requested.
3.3
SSLSocket.selected_alpn_protocol()
Return the protocol that was selected during the TLS handshake. If SSLContext.set_alpn_protocols
was not called, if the other party does not support ALPN, if this socket does not support any of the client's proposed protocols, or if the handshake has not happened yet, None
is returned.
3.5
SSLSocket.selected_npn_protocol()
Return the higher-level protocol that was selected during the TLS/SSL handshake. If SSLContext.set_npn_protocols
was not called, or if the other party does not support NPN, or if the handshake has not yet happened, this will return None
.
3.3
3.10
NPN has been superseded by ALPN
SSLSocket.unwrap()
Performs the SSL shutdown handshake, which removes the TLS layer from the underlying socket, and returns the underlying socket object. This can be used to go from encrypted operation over a connection to unencrypted. The returned socket should always be used for further communication with the other side of the connection, rather than the original socket.
SSLSocket.verify_client_post_handshake()
Requests post-handshake authentication (PHA) from a TLS 1.3 client. PHA can only be initiated for a TLS 1.3 connection from a server-side socket, after the initial TLS handshake and with PHA enabled on both sides, see SSLContext.post_handshake_auth
.
The method does not perform a cert exchange immediately. The server-side sends a CertificateRequest during the next write event and expects the client to respond with a certificate on the next read event.
If any precondition isn't met (e.g. not TLS 1.3, PHA not enabled), an SSLError
is raised.
Note
Only available with OpenSSL 1.1.1 and TLS 1.3 enabled. Without TLS 1.3 support, the method raises NotImplementedError
.
3.8
SSLSocket.version()
Return the actual SSL protocol version negotiated by the connection as a string, or None
is no secure connection is established. As of this writing, possible return values include "SSLv2"
, "SSLv3"
, "TLSv1"
, "TLSv1.1"
and "TLSv1.2"
. Recent OpenSSL versions may define more return values.
3.5
SSLSocket.pending()
Returns the number of already decrypted bytes available for read, pending on the connection.
SSLSocket.context
The SSLContext
object this SSL socket is tied to. If the SSL socket was created using the deprecated wrap_socket
function (rather than SSLContext.wrap_socket
), this is a custom context object created for this SSL socket.
3.2
SSLSocket.server_side
A boolean which is True
for server-side sockets and False
for client-side sockets.
3.2
SSLSocket.server_hostname
Hostname of the server: str
type, or None
for server-side socket or if the hostname was not specified in the constructor.
3.2
3.7 The attribute is now always ASCII text. When server_hostname
is an internationalized domain name (IDN), this attribute now stores the A-label form ("xn--pythn-mua.org"
), rather than the U-label form ("pythön.org"
).
SSLSocket.session
The SSLSession
for this SSL connection. The session is available for client and server side sockets after the TLS handshake has been performed. For client sockets the session can be set before ~SSLSocket.do_handshake
has been called to reuse a session.
3.6
SSLSocket.session_reused
3.6
3.2
An SSL context holds various data longer-lived than single SSL connections, such as SSL configuration options, certificate(s) and private key(s). It also manages a cache of SSL sessions for server-side sockets, in order to speed up repeated connections from the same clients.
Create a new SSL context. You may pass protocol which must be one of the PROTOCOL_*
constants defined in this module. The parameter specifies which version of the SSL protocol to use. Typically, the server chooses a particular protocol version, and the client must adapt to the server's choice. Most of the versions are not interoperable with the other versions. If not specified, the default is PROTOCOL_TLS
; it provides the most compatibility with other versions.
Here's a table showing which versions in a client (down the side) can connect to which versions in a server (along the top):
client / server SSLv2 SSLv3 TLS TLSv1 TLSv1.1 TLSv1.2 SSLv2
yes
no
no
no
no
no SSLv3
no
yes
no
no
no
no TLS (SSLv23)
no
no
yes
yes
yes
yes TLSv1
no
no
yes
yes
no
no TLSv1.1
no
no
yes
no
yes
no TLSv1.2
no
no
yes
no
no
yes
Footnotes
create_default_context
lets the ssl
module choose security settings for a given purpose.
3.6
The context is created with secure default values. The options OP_NO_COMPRESSION
, OP_CIPHER_SERVER_PREFERENCE
, OP_SINGLE_DH_USE
, OP_SINGLE_ECDH_USE
, OP_NO_SSLv2
(except for PROTOCOL_SSLv2
), and OP_NO_SSLv3
(except for PROTOCOL_SSLv3
) are set by default. The initial cipher suite list contains only HIGH
ciphers, no NULL
ciphers and no MD5
ciphers (except for PROTOCOL_SSLv2
).
3.10
SSLContext
without protocol argument is deprecated. The context class will either require PROTOCOL_TLS_CLIENT
or PROTOCOL_TLS_SERVER
protocol in the future.
3.10
The default cipher suites now include only secure AES and ChaCha20 ciphers with forward secrecy and security level 2. RSA and DH keys with less than 2048 bits and ECC keys with less than 224 bits are prohibited. PROTOCOL_TLS
, PROTOCOL_TLS_CLIENT
, and PROTOCOL_TLS_SERVER
use TLS 1.2 as minimum TLS version.
SSLContext
objects have the following methods and attributes:
SSLContext.cert_store_stats()
Get statistics about quantities of loaded X.509 certificates, count of X.509 certificates flagged as CA certificates and certificate revocation lists as dictionary.
Example for a context with one CA cert and one other cert:
>>> context.cert_store_stats()
{'crl': 0, 'x509_ca': 1, 'x509': 2}
3.4
SSLContext.load_cert_chain(certfile, keyfile=None, password=None)
Load a private key and the corresponding certificate. The certfile string must be the path to a single file in PEM format containing the certificate as well as any number of CA certificates needed to establish the certificate's authenticity. The keyfile string, if present, must point to a file containing the private key in. Otherwise the private key will be taken from certfile as well. See the discussion of ssl-certificates
for more information on how the certificate is stored in the certfile.
The password argument may be a function to call to get the password for decrypting the private key. It will only be called if the private key is encrypted and a password is necessary. It will be called with no arguments, and it should return a string, bytes, or bytearray. If the return value is a string it will be encoded as UTF-8 before using it to decrypt the key. Alternatively a string, bytes, or bytearray value may be supplied directly as the password argument. It will be ignored if the private key is not encrypted and no password is needed.
If the password argument is not specified and a password is required, OpenSSL's built-in password prompting mechanism will be used to interactively prompt the user for a password.
An SSLError
is raised if the private key doesn't match with the certificate.
3.3 New optional argument password.
SSLContext.load_default_certs(purpose=Purpose.SERVER_AUTH)
Load a set of default "certification authority" (CA) certificates from default locations. On Windows it loads CA certs from the CA
and ROOT
system stores. On other systems it calls SSLContext.set_default_verify_paths
. In the future the method may load CA certificates from other locations, too.
The purpose flag specifies what kind of CA certificates are loaded. The default settings Purpose.SERVER_AUTH
loads certificates, that are flagged and trusted for TLS web server authentication (client side sockets). Purpose.CLIENT_AUTH
loads CA certificates for client certificate verification on the server side.
3.4
SSLContext.load_verify_locations(cafile=None, capath=None, cadata=None)
Load a set of "certification authority" (CA) certificates used to validate other peers' certificates when verify_mode
is other than CERT_NONE
. At least one of cafile or capath must be specified.
This method can also load certification revocation lists (CRLs) in PEM or DER format. In order to make use of CRLs, SSLContext.verify_flags
must be configured properly.
The cafile string, if present, is the path to a file of concatenated CA certificates in PEM format. See the discussion of ssl-certificates
for more information about how to arrange the certificates in this file.
The capath string, if present, is the path to a directory containing several CA certificates in PEM format, following an OpenSSL specific layout.
The cadata object, if present, is either an ASCII string of one or more PEM-encoded certificates or a bytes-like object
of DER-encoded certificates. Like with capath extra lines around PEM-encoded certificates are ignored but at least one certificate must be present.
3.4 New optional argument cadata
SSLContext.get_ca_certs(binary_form=False)
Get a list of loaded "certification authority" (CA) certificates. If the binary_form
parameter is False
each list entry is a dict like the output of SSLSocket.getpeercert
. Otherwise the method returns a list of DER-encoded certificates. The returned list does not contain certificates from capath unless a certificate was requested and loaded by a SSL connection.
Note
Certificates in a capath directory aren't loaded unless they have been used at least once.
3.4
SSLContext.get_ciphers()
Get a list of enabled ciphers. The list is in order of cipher priority. See SSLContext.set_ciphers
.
Example:
>>> ctx = ssl.SSLContext(ssl.PROTOCOL_SSLv23)
>>> ctx.set_ciphers('ECDHE+AESGCM:!ECDSA')
>>> ctx.get_ciphers()
[{'aead': True,
'alg_bits': 256,
'auth': 'auth-rsa',
'description': 'ECDHE-RSA-AES256-GCM-SHA384 TLSv1.2 Kx=ECDH Au=RSA '
'Enc=AESGCM(256) Mac=AEAD',
'digest': None,
'id': 50380848,
'kea': 'kx-ecdhe',
'name': 'ECDHE-RSA-AES256-GCM-SHA384',
'protocol': 'TLSv1.2',
'strength_bits': 256,
'symmetric': 'aes-256-gcm'},
{'aead': True,
'alg_bits': 128,
'auth': 'auth-rsa',
'description': 'ECDHE-RSA-AES128-GCM-SHA256 TLSv1.2 Kx=ECDH Au=RSA '
'Enc=AESGCM(128) Mac=AEAD',
'digest': None,
'id': 50380847,
'kea': 'kx-ecdhe',
'name': 'ECDHE-RSA-AES128-GCM-SHA256',
'protocol': 'TLSv1.2',
'strength_bits': 128,
'symmetric': 'aes-128-gcm'}]
3.6
SSLContext.set_default_verify_paths()
Load a set of default "certification authority" (CA) certificates from a filesystem path defined when building the OpenSSL library. Unfortunately, there's no easy way to know whether this method succeeds: no error is returned if no certificates are to be found. When the OpenSSL library is provided as part of the operating system, though, it is likely to be configured properly.
SSLContext.set_ciphers(ciphers)
Set the available ciphers for sockets created with this context. It should be a string in the OpenSSL cipher list format. If no cipher can be selected (because compile-time options or other configuration forbids use of all the specified ciphers), an SSLError
will be raised.
Note
when connected, the SSLSocket.cipher
method of SSL sockets will give the currently selected cipher.
TLS 1.3 cipher suites cannot be disabled with ~SSLContext.set_ciphers
.
SSLContext.set_alpn_protocols(protocols)
Specify which protocols the socket should advertise during the SSL/TLS handshake. It should be a list of ASCII strings, like ['http/1.1', 'spdy/2']
, ordered by preference. The selection of a protocol will happen during the handshake, and will play out according to 7301
. After a successful handshake, the SSLSocket.selected_alpn_protocol
method will return the agreed-upon protocol.
This method will raise NotImplementedError
if HAS_ALPN
is False
.
3.5
SSLContext.set_npn_protocols(protocols)
Specify which protocols the socket should advertise during the SSL/TLS handshake. It should be a list of strings, like ['http/1.1', 'spdy/2']
, ordered by preference. The selection of a protocol will happen during the handshake, and will play out according to the Application Layer Protocol Negotiation. After a successful handshake, the SSLSocket.selected_npn_protocol
method will return the agreed-upon protocol.
This method will raise NotImplementedError
if HAS_NPN
is False
.
3.3
3.10
NPN has been superseded by ALPN
SSLContext.sni_callback
Register a callback function that will be called after the TLS Client Hello handshake message has been received by the SSL/TLS server when the TLS client specifies a server name indication. The server name indication mechanism is specified in 6066
section 3 - Server Name Indication.
Only one callback can be set per SSLContext
. If sni_callback is set to None
then the callback is disabled. Calling this function a subsequent time will disable the previously registered callback.
The callback function will be called with three arguments; the first being the ssl.SSLSocket
, the second is a string that represents the server name that the client is intending to communicate (or None
if the TLS Client Hello does not contain a server name) and the third argument is the original SSLContext
. The server name argument is text. For internationalized domain name, the server name is an IDN A-label ("xn--pythn-mua.org"
).
A typical use of this callback is to change the ssl.SSLSocket
's SSLSocket.context
attribute to a new object of type SSLContext
representing a certificate chain that matches the server name.
Due to the early negotiation phase of the TLS connection, only limited methods and attributes are usable like SSLSocket.selected_alpn_protocol
and SSLSocket.context
. SSLSocket.getpeercert
, SSLSocket.getpeercert
, SSLSocket.cipher
and SSLSocket.compress
methods require that the TLS connection has progressed beyond the TLS Client Hello and therefore will not contain return meaningful values nor can they be called safely.
The sni_callback function must return None
to allow the TLS negotiation to continue. If a TLS failure is required, a constant ALERT_DESCRIPTION_* <ALERT_DESCRIPTION_INTERNAL_ERROR>
can be returned. Other return values will result in a TLS fatal error with ALERT_DESCRIPTION_INTERNAL_ERROR
.
If an exception is raised from the sni_callback function the TLS connection will terminate with a fatal TLS alert message ALERT_DESCRIPTION_HANDSHAKE_FAILURE
.
This method will raise NotImplementedError
if the OpenSSL library had OPENSSL_NO_TLSEXT defined when it was built.
3.7
SSLContext.set_servername_callback(server_name_callback)
This is a legacy API retained for backwards compatibility. When possible, you should use sni_callback
instead. The given server_name_callback is similar to sni_callback, except that when the server hostname is an IDN-encoded internationalized domain name, the server_name_callback receives a decoded U-label ("pythön.org"
).
If there is an decoding error on the server name, the TLS connection will terminate with an ALERT_DESCRIPTION_INTERNAL_ERROR
fatal TLS alert message to the client.
3.4
SSLContext.load_dh_params(dhfile)
Load the key generation parameters for Diffie-Hellman (DH) key exchange. Using DH key exchange improves forward secrecy at the expense of computational resources (both on the server and on the client). The dhfile parameter should be the path to a file containing DH parameters in PEM format.
This setting doesn't apply to client sockets. You can also use the OP_SINGLE_DH_USE
option to further improve security.
3.3
SSLContext.set_ecdh_curve(curve_name)
Set the curve name for Elliptic Curve-based Diffie-Hellman (ECDH) key exchange. ECDH is significantly faster than regular DH while arguably as secure. The curve_name parameter should be a string describing a well-known elliptic curve, for example prime256v1
for a widely supported curve.
This setting doesn't apply to client sockets. You can also use the OP_SINGLE_ECDH_USE
option to further improve security.
This method is not available if HAS_ECDH
is False
.
3.3
SSL/TLS & Perfect Forward Secrecy Vincent Bernat.
SSLContext.wrap_socket(sock, server_side=False, do_handshake_on_connect=True, suppress_ragged_eofs=True, server_hostname=None, session=None)
Wrap an existing Python socket sock and return an instance of SSLContext.sslsocket_class
(default SSLSocket
). The returned SSL socket is tied to the context, its settings and certificates. sock must be a ~socket.SOCK_STREAM
socket; other socket types are unsupported.
The parameter server_side
is a boolean which identifies whether server-side or client-side behavior is desired from this socket.
For client-side sockets, the context construction is lazy; if the underlying socket isn't connected yet, the context construction will be performed after connect
is called on the socket. For server-side sockets, if the socket has no remote peer, it is assumed to be a listening socket, and the server-side SSL wrapping is automatically performed on client connections accepted via the accept
method. The method may raise SSLError
.
On client connections, the optional parameter server_hostname specifies the hostname of the service which we are connecting to. This allows a single server to host multiple SSL-based services with distinct certificates, quite similarly to HTTP virtual hosts. Specifying server_hostname will raise a ValueError
if server_side is true.
The parameter do_handshake_on_connect
specifies whether to do the SSL handshake automatically after doing a socket.connect
, or whether the application program will call it explicitly, by invoking the SSLSocket.do_handshake
method. Calling SSLSocket.do_handshake
explicitly gives the program control over the blocking behavior of the socket I/O involved in the handshake.
The parameter suppress_ragged_eofs
specifies how the SSLSocket.recv
method should signal unexpected EOF from the other end of the connection. If specified as True
(the default), it returns a normal EOF (an empty bytes object) in response to unexpected EOF errors raised from the underlying socket; if False
, it will raise the exceptions back to the caller.
session, see ~SSLSocket.session
.
3.5 Always allow a server_hostname to be passed, even if OpenSSL does not have SNI.
3.6 session argument was added.
3.7 The method returns on instance of SSLContext.sslsocket_class
instead of hard-coded SSLSocket
.
SSLContext.sslsocket_class
The return type of SSLContext.wrap_socket
, defaults to SSLSocket
. The attribute can be overridden on instance of class in order to return a custom subclass of SSLSocket
.
3.7
SSLContext.wrap_bio(incoming, outgoing, server_side=False, server_hostname=None, session=None)
Wrap the BIO objects incoming and outgoing and return an instance of SSLContext.sslobject_class
(default SSLObject
). The SSL routines will read input data from the incoming BIO and write data to the outgoing BIO.
The server_side, server_hostname and session parameters have the same meaning as in SSLContext.wrap_socket
.
3.6 session argument was added.
3.7 The method returns on instance of SSLContext.sslobject_class
instead of hard-coded SSLObject
.
SSLContext.sslobject_class
The return type of SSLContext.wrap_bio
, defaults to SSLObject
. The attribute can be overridden on instance of class in order to return a custom subclass of SSLObject
.
3.7
SSLContext.session_stats()
Get statistics about the SSL sessions created or managed by this context. A dictionary is returned which maps the names of each piece of information to their numeric values. For example, here is the total number of hits and misses in the session cache since the context was created:
>>> stats = context.session_stats()
>>> stats['hits'], stats['misses']
(0, 0)
SSLContext.check_hostname
Whether to match the peer cert's hostname in SSLSocket.do_handshake
. The context's ~SSLContext.verify_mode
must be set to CERT_OPTIONAL
or CERT_REQUIRED
, and you must pass server_hostname to ~SSLContext.wrap_socket
in order to match the hostname. Enabling hostname checking automatically sets ~SSLContext.verify_mode
from CERT_NONE
to CERT_REQUIRED
. It cannot be set back to CERT_NONE
as long as hostname checking is enabled. The PROTOCOL_TLS_CLIENT
protocol enables hostname checking by default. With other protocols, hostname checking must be enabled explicitly.
Example:
import socket, ssl
context = ssl.SSLContext(ssl.PROTOCOL_TLSv1_2)
context.verify_mode = ssl.CERT_REQUIRED
context.check_hostname = True
context.load_default_certs()
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
ssl_sock = context.wrap_socket(s, server_hostname='www.verisign.com')
ssl_sock.connect(('www.verisign.com', 443))
3.4
3.7
~SSLContext.verify_mode
is now automatically changed to CERT_REQUIRED
when hostname checking is enabled and ~SSLContext.verify_mode
is CERT_NONE
. Previously the same operation would have failed with a ValueError
.
SSLContext.keylog_filename
Write TLS keys to a keylog file, whenever key material is generated or received. The keylog file is designed for debugging purposes only. The file format is specified by NSS and used by many traffic analyzers such as Wireshark. The log file is opened in append-only mode. Writes are synchronized between threads, but not between processes.
3.8
SSLContext.maximum_version
A TLSVersion
enum member representing the highest supported TLS version. The value defaults to TLSVersion.MAXIMUM_SUPPORTED
. The attribute is read-only for protocols other than PROTOCOL_TLS
, PROTOCOL_TLS_CLIENT
, and PROTOCOL_TLS_SERVER
.
The attributes ~SSLContext.maximum_version
, ~SSLContext.minimum_version
and SSLContext.options
all affect the supported SSL and TLS versions of the context. The implementation does not prevent invalid combination. For example a context with OP_NO_TLSv1_2
in ~SSLContext.options
and ~SSLContext.maximum_version
set to TLSVersion.TLSv1_2
will not be able to establish a TLS 1.2 connection.
3.7
SSLContext.minimum_version
Like SSLContext.maximum_version
except it is the lowest supported version or TLSVersion.MINIMUM_SUPPORTED
.
3.7
SSLContext.num_tickets
Control the number of TLS 1.3 session tickets of a PROTOCOL_TLS_SERVER
context. The setting has no impact on TLS 1.0 to 1.2 connections.
3.8
SSLContext.options
An integer representing the set of SSL options enabled on this context. The default value is OP_ALL
, but you can specify other options such as OP_NO_SSLv2
by ORing them together.
3.6 SSLContext.options
returns Options
flags:
>>> ssl.create_default_context().options # doctest: +SKIP <Options.OP_ALLOP_NO_SSLv2|OP_NO_COMPRESSION: 2197947391>
3.7
All OP_NO_SSL*
and OP_NO_TLS*
options have been deprecated since Python 3.7. Use SSLContext.minimum_version
and SSLContext.maximum_version
instead.
SSLContext.post_handshake_auth
Enable TLS 1.3 post-handshake client authentication. Post-handshake auth is disabled by default and a server can only request a TLS client certificate during the initial handshake. When enabled, a server may request a TLS client certificate at any time after the handshake.
When enabled on client-side sockets, the client signals the server that it supports post-handshake authentication.
When enabled on server-side sockets, SSLContext.verify_mode
must be set to CERT_OPTIONAL
or CERT_REQUIRED
, too. The actual client cert exchange is delayed until SSLSocket.verify_client_post_handshake
is called and some I/O is performed.
3.8
SSLContext.protocol
The protocol version chosen when constructing the context. This attribute is read-only.
SSLContext.hostname_checks_common_name
Whether ~SSLContext.check_hostname
falls back to verify the cert's subject common name in the absence of a subject alternative name extension (default: true).
3.7
3.10
The flag had no effect with OpenSSL before version 1.1.1k. Python 3.8.9, 3.9.3, and 3.10 include workarounds for previous versions.
SSLContext.security_level
An integer representing the security level for the context. This attribute is read-only.
3.10
SSLContext.verify_flags
The flags for certificate verification operations. You can set flags like VERIFY_CRL_CHECK_LEAF
by ORing them together. By default OpenSSL does neither require nor verify certificate revocation lists (CRLs).
3.4
3.6 SSLContext.verify_flags
returns VerifyFlags
flags:
>>> ssl.create_default_context().verify_flags # doctest: +SKIP ssl.VERIFY_X509_TRUSTED_FIRST
SSLContext.verify_mode
Whether to try to verify other peers' certificates and how to behave if verification fails. This attribute must be one of CERT_NONE
, CERT_OPTIONAL
or CERT_REQUIRED
.
3.6 SSLContext.verify_mode
returns VerifyMode
enum:
>>> ssl.create_default_context().verify_mode ssl.CERT_REQUIRED
single: certificates
single: X509 certificate
Certificates in general are part of a public-key / private-key system. In this system, each principal, (which may be a machine, or a person, or an organization) is assigned a unique two-part encryption key. One part of the key is public, and is called the public key; the other part is kept secret, and is called the private key. The two parts are related, in that if you encrypt a message with one of the parts, you can decrypt it with the other part, and only with the other part.
A certificate contains information about two principals. It contains the name of a subject, and the subject's public key. It also contains a statement by a second principal, the issuer, that the subject is who they claim to be, and that this is indeed the subject's public key. The issuer's statement is signed with the issuer's private key, which only the issuer knows. However, anyone can verify the issuer's statement by finding the issuer's public key, decrypting the statement with it, and comparing it to the other information in the certificate. The certificate also contains information about the time period over which it is valid. This is expressed as two fields, called "notBefore" and "notAfter".
In the Python use of certificates, a client or server can use a certificate to prove who they are. The other side of a network connection can also be required to produce a certificate, and that certificate can be validated to the satisfaction of the client or server that requires such validation. The connection attempt can be set to raise an exception if the validation fails. Validation is done automatically, by the underlying OpenSSL framework; the application need not concern itself with its mechanics. But the application does usually need to provide sets of certificates to allow this process to take place.
Python uses files to contain certificates. They should be formatted as "PEM" (see 1422
), which is a base-64 encoded form wrapped with a header line and a footer line:
-----BEGIN CERTIFICATE-----
... (certificate in base64 PEM encoding) ...
-----END CERTIFICATE-----
The Python files which contain certificates can contain a sequence of certificates, sometimes called a certificate chain. This chain should start with the specific certificate for the principal who "is" the client or server, and then the certificate for the issuer of that certificate, and then the certificate for the issuer of that certificate, and so on up the chain till you get to a certificate which is self-signed, that is, a certificate which has the same subject and issuer, sometimes called a root certificate. The certificates should just be concatenated together in the certificate file. For example, suppose we had a three certificate chain, from our server certificate to the certificate of the certification authority that signed our server certificate, to the root certificate of the agency which issued the certification authority's certificate:
-----BEGIN CERTIFICATE-----
... (certificate for your server)...
-----END CERTIFICATE-----
-----BEGIN CERTIFICATE-----
... (the certificate for the CA)...
-----END CERTIFICATE-----
-----BEGIN CERTIFICATE-----
... (the root certificate for the CA's issuer)...
-----END CERTIFICATE-----
If you are going to require validation of the other side of the connection's certificate, you need to provide a "CA certs" file, filled with the certificate chains for each issuer you are willing to trust. Again, this file just contains these chains concatenated together. For validation, Python will use the first chain it finds in the file which matches. The platform's certificates file can be used by calling SSLContext.load_default_certs
, this is done automatically with .create_default_context
.
Often the private key is stored in the same file as the certificate; in this case, only the certfile
parameter to SSLContext.load_cert_chain
and wrap_socket
needs to be passed. If the private key is stored with the certificate, it should come before the first certificate in the certificate chain:
-----BEGIN RSA PRIVATE KEY-----
... (private key in base64 encoding) ...
-----END RSA PRIVATE KEY-----
-----BEGIN CERTIFICATE-----
... (certificate in base64 PEM encoding) ...
-----END CERTIFICATE-----
If you are going to create a server that provides SSL-encrypted connection services, you will need to acquire a certificate for that service. There are many ways of acquiring appropriate certificates, such as buying one from a certification authority. Another common practice is to generate a self-signed certificate. The simplest way to do this is with the OpenSSL package, using something like the following:
% openssl req -new -x509 -days 365 -nodes -out cert.pem -keyout cert.pem
Generating a 1024 bit RSA private key
.......++++++
.............................++++++
writing new private key to 'cert.pem'
-----
You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter '.', the field will be left blank.
-----
Country Name (2 letter code) [AU]:US
State or Province Name (full name) [Some-State]:MyState
Locality Name (eg, city) []:Some City
Organization Name (eg, company) [Internet Widgits Pty Ltd]:My Organization, Inc.
Organizational Unit Name (eg, section) []:My Group
Common Name (eg, YOUR name) []:myserver.mygroup.myorganization.com
Email Address []:ops@myserver.mygroup.myorganization.com
%
The disadvantage of a self-signed certificate is that it is its own root certificate, and no one else will have it in their cache of known (and trusted) root certificates.
To test for the presence of SSL support in a Python installation, user code should use the following idiom:
try:
import ssl
except ImportError:
pass
else:
... # do something that requires SSL support
This example creates a SSL context with the recommended security settings for client sockets, including automatic certificate verification:
>>> context = ssl.create_default_context()
If you prefer to tune security settings yourself, you might create a context from scratch (but beware that you might not get the settings right):
>>> context = ssl.SSLContext(ssl.PROTOCOL_TLS_CLIENT)
>>> context.load_verify_locations("/etc/ssl/certs/ca-bundle.crt")
(this snippet assumes your operating system places a bundle of all CA certificates in /etc/ssl/certs/ca-bundle.crt
; if not, you'll get an error and have to adjust the location)
The PROTOCOL_TLS_CLIENT
protocol configures the context for cert validation and hostname verification. ~SSLContext.verify_mode
is set to CERT_REQUIRED
and ~SSLContext.check_hostname
is set to True
. All other protocols create SSL contexts with insecure defaults.
When you use the context to connect to a server, CERT_REQUIRED
and ~SSLContext.check_hostname
validate the server certificate: it ensures that the server certificate was signed with one of the CA certificates, checks the signature for correctness, and verifies other properties like validity and identity of the hostname:
>>> conn = context.wrap_socket(socket.socket(socket.AF_INET),
... server_hostname="www.python.org")
>>> conn.connect(("www.python.org", 443))
You may then fetch the certificate:
>>> cert = conn.getpeercert()
Visual inspection shows that the certificate does identify the desired service (that is, the HTTPS host www.python.org
):
>>> pprint.pprint(cert)
{'OCSP': ('http://ocsp.digicert.com',),
'caIssuers': ('http://cacerts.digicert.com/DigiCertSHA2ExtendedValidationServerCA.crt',),
'crlDistributionPoints': ('http://crl3.digicert.com/sha2-ev-server-g1.crl',
'http://crl4.digicert.com/sha2-ev-server-g1.crl'),
'issuer': ((('countryName', 'US'),),
(('organizationName', 'DigiCert Inc'),),
(('organizationalUnitName', 'www.digicert.com'),),
(('commonName', 'DigiCert SHA2 Extended Validation Server CA'),)),
'notAfter': 'Sep 9 12:00:00 2016 GMT',
'notBefore': 'Sep 5 00:00:00 2014 GMT',
'serialNumber': '01BB6F00122B177F36CAB49CEA8B6B26',
'subject': ((('businessCategory', 'Private Organization'),),
(('1.3.6.1.4.1.311.60.2.1.3', 'US'),),
(('1.3.6.1.4.1.311.60.2.1.2', 'Delaware'),),
(('serialNumber', '3359300'),),
(('streetAddress', '16 Allen Rd'),),
(('postalCode', '03894-4801'),),
(('countryName', 'US'),),
(('stateOrProvinceName', 'NH'),),
(('localityName', 'Wolfeboro'),),
(('organizationName', 'Python Software Foundation'),),
(('commonName', 'www.python.org'),)),
'subjectAltName': (('DNS', 'www.python.org'),
('DNS', 'python.org'),
('DNS', 'pypi.org'),
('DNS', 'docs.python.org'),
('DNS', 'testpypi.org'),
('DNS', 'bugs.python.org'),
('DNS', 'wiki.python.org'),
('DNS', 'hg.python.org'),
('DNS', 'mail.python.org'),
('DNS', 'packaging.python.org'),
('DNS', 'pythonhosted.org'),
('DNS', 'www.pythonhosted.org'),
('DNS', 'test.pythonhosted.org'),
('DNS', 'us.pycon.org'),
('DNS', 'id.python.org')),
'version': 3}
Now the SSL channel is established and the certificate verified, you can proceed to talk with the server:
>>> conn.sendall(b"HEAD / HTTP/1.0\r\nHost: linuxfr.org\r\n\r\n")
>>> pprint.pprint(conn.recv(1024).split(b"\r\n"))
[b'HTTP/1.1 200 OK',
b'Date: Sat, 18 Oct 2014 18:27:20 GMT',
b'Server: nginx',
b'Content-Type: text/html; charset=utf-8',
b'X-Frame-Options: SAMEORIGIN',
b'Content-Length: 45679',
b'Accept-Ranges: bytes',
b'Via: 1.1 varnish',
b'Age: 2188',
b'X-Served-By: cache-lcy1134-LCY',
b'X-Cache: HIT',
b'X-Cache-Hits: 11',
b'Vary: Cookie',
b'Strict-Transport-Security: max-age=63072000; includeSubDomains',
b'Connection: close',
b'',
b'']
See the discussion of ssl-security
below.
For server operation, typically you'll need to have a server certificate, and private key, each in a file. You'll first create a context holding the key and the certificate, so that clients can check your authenticity. Then you'll open a socket, bind it to a port, call listen
on it, and start waiting for clients to connect:
import socket, ssl
context = ssl.create_default_context(ssl.Purpose.CLIENT_AUTH)
context.load_cert_chain(certfile="mycertfile", keyfile="mykeyfile")
bindsocket = socket.socket()
bindsocket.bind(('myaddr.mydomain.com', 10023))
bindsocket.listen(5)
When a client connects, you'll call accept
on the socket to get the new socket from the other end, and use the context's SSLContext.wrap_socket
method to create a server-side SSL socket for the connection:
while True:
newsocket, fromaddr = bindsocket.accept()
connstream = context.wrap_socket(newsocket, server_side=True)
try:
deal_with_client(connstream)
finally:
connstream.shutdown(socket.SHUT_RDWR)
connstream.close()
Then you'll read data from the connstream
and do something with it till you are finished with the client (or the client is finished with you):
def deal_with_client(connstream):
data = connstream.recv(1024)
# empty data means the client is finished with us
while data:
if not do_something(connstream, data):
# we'll assume do_something returns False
# when we're finished with client
break
data = connstream.recv(1024)
# finished with client
And go back to listening for new client connections (of course, a real server would probably handle each client connection in a separate thread, or put the sockets in non-blocking mode <ssl-nonblocking>
and use an event loop).
SSL sockets behave slightly different than regular sockets in non-blocking mode. When working with non-blocking sockets, there are thus several things you need to be aware of:
Most
SSLSocket
methods will raise eitherSSLWantWriteError
orSSLWantReadError
instead ofBlockingIOError
if an I/O operation would block.SSLWantReadError
will be raised if a read operation on the underlying socket is necessary, andSSLWantWriteError
for a write operation on the underlying socket. Note that attempts to write to an SSL socket may require reading from the underlying socket first, and attempts to read from the SSL socket may require a prior write to the underlying socket.3.5
In earlier Python versions, the
!SSLSocket.send
method returned zero instead of raisingSSLWantWriteError
orSSLWantReadError
.- Calling
~select.select
tells you that the OS-level socket can be read from (or written to), but it does not imply that there is sufficient data at the upper SSL layer. For example, only part of an SSL frame might have arrived. Therefore, you must be ready to handleSSLSocket.recv
andSSLSocket.send
failures, and retry after another call to~select.select
. Conversely, since the SSL layer has its own framing, a SSL socket may still have data available for reading without
~select.select
being aware of it. Therefore, you should first callSSLSocket.recv
to drain any potentially available data, and then only block on a~select.select
call if still necessary.(of course, similar provisions apply when using other primitives such as
~select.poll
, or those in theselectors
module)The SSL handshake itself will be non-blocking: the
SSLSocket.do_handshake
method has to be retried until it returns successfully. Here is a synopsis using~select.select
to wait for the socket's readiness:while True: try: sock.do_handshake() break except ssl.SSLWantReadError: select.select([sock], [], []) except ssl.SSLWantWriteError: select.select([], [sock], [])
The asyncio
module supports non-blocking SSL sockets
<ssl-nonblocking>
and provides a higher level API. It polls for events using the selectors
module and handles SSLWantWriteError
, SSLWantReadError
and BlockingIOError
exceptions. It runs the SSL handshake asynchronously as well.
3.5
Ever since the SSL module was introduced in Python 2.6, the SSLSocket
class has provided two related but distinct areas of functionality:
- SSL protocol handling
- Network IO
The network IO API is identical to that provided by socket.socket
, from which SSLSocket
also inherits. This allows an SSL socket to be used as a drop-in replacement for a regular socket, making it very easy to add SSL support to an existing application.
Combining SSL protocol handling and network IO usually works well, but there are some cases where it doesn't. An example is async IO frameworks that want to use a different IO multiplexing model than the "select/poll on a file descriptor" (readiness based) model that is assumed by socket.socket
and by the internal OpenSSL socket IO routines. This is mostly relevant for platforms like Windows where this model is not efficient. For this purpose, a reduced scope variant of SSLSocket
called SSLObject
is provided.
A reduced-scope variant of SSLSocket
representing an SSL protocol instance that does not contain any network IO methods. This class is typically used by framework authors that want to implement asynchronous IO for SSL through memory buffers.
This class implements an interface on top of a low-level SSL object as implemented by OpenSSL. This object captures the state of an SSL connection but does not provide any network IO itself. IO needs to be performed through separate "BIO" objects which are OpenSSL's IO abstraction layer.
This class has no public constructor. An SSLObject
instance must be created using the ~SSLContext.wrap_bio
method. This method will create the SSLObject
instance and bind it to a pair of BIOs. The incoming BIO is used to pass data from Python to the SSL protocol instance, while the outgoing BIO is used to pass data the other way around.
The following methods are available:
~SSLSocket.context
~SSLSocket.server_side
~SSLSocket.server_hostname
~SSLSocket.session
~SSLSocket.session_reused
~SSLSocket.read
~SSLSocket.write
~SSLSocket.getpeercert
~SSLSocket.selected_alpn_protocol
~SSLSocket.selected_npn_protocol
~SSLSocket.cipher
~SSLSocket.shared_ciphers
~SSLSocket.compression
~SSLSocket.pending
~SSLSocket.do_handshake
~SSLSocket.verify_client_post_handshake
~SSLSocket.unwrap
~SSLSocket.get_channel_binding
~SSLSocket.version
When compared to SSLSocket
, this object lacks the following features:
- Any form of network IO;
recv()
andsend()
read and write only to the underlyingMemoryBIO
buffers. - There is no do_handshake_on_connect machinery. You must always manually call
~SSLSocket.do_handshake
to start the handshake. - There is no handling of suppress_ragged_eofs. All end-of-file conditions that are in violation of the protocol are reported via the
SSLEOFError
exception. - The method
~SSLSocket.unwrap
call does not return anything, unlike for an SSL socket where it returns the underlying socket. - The server_name_callback callback passed to
SSLContext.set_servername_callback
will get anSSLObject
instance instead of aSSLSocket
instance as its first parameter.
Some notes related to the use of SSLObject
:
- All IO on an
SSLObject
isnon-blocking <ssl-nonblocking>
. This means that for example~SSLSocket.read
will raise anSSLWantReadError
if it needs more data than the incoming BIO has available. - There is no module-level
wrap_bio()
call like there is for~SSLContext.wrap_socket
. AnSSLObject
is always created via anSSLContext
.
3.7 SSLObject
instances must to created with ~SSLContext.wrap_bio
. In earlier versions, it was possible to create instances directly. This was never documented or officially supported.
An SSLObject communicates with the outside world using memory buffers. The class MemoryBIO
provides a memory buffer that can be used for this purpose. It wraps an OpenSSL memory BIO (Basic IO) object:
A memory buffer that can be used to pass data between Python and an SSL protocol instance.
MemoryBIO.pending
Return the number of bytes currently in the memory buffer.
MemoryBIO.eof
A boolean indicating whether the memory BIO is current at the end-of-file position.
MemoryBIO.read(n=-1)
Read up to n bytes from the memory buffer. If n is not specified or negative, all bytes are returned.
MemoryBIO.write(buf)
Write the bytes from buf to the memory BIO. The buf argument must be an object supporting the buffer protocol.
The return value is the number of bytes written, which is always equal to the length of buf.
MemoryBIO.write_eof()
Write an EOF marker to the memory BIO. After this method has been called, it is illegal to call ~MemoryBIO.write
. The attribute eof
will become true after all data currently in the buffer has been read.
3.6
Session object used by ~SSLSocket.session
.
id
time
timeout
ticket_lifetime_hint
has_ticket
For client use, if you don't have any special requirements for your security policy, it is highly recommended that you use the create_default_context
function to create your SSL context. It will load the system's trusted CA certificates, enable certificate validation and hostname checking, and try to choose reasonably secure protocol and cipher settings.
For example, here is how you would use the smtplib.SMTP
class to create a trusted, secure connection to a SMTP server:
>>> import ssl, smtplib
>>> smtp = smtplib.SMTP("mail.python.org", port=587)
>>> context = ssl.create_default_context()
>>> smtp.starttls(context=context)
(220, b'2.0.0 Ready to start TLS')
If a client certificate is needed for the connection, it can be added with SSLContext.load_cert_chain
.
By contrast, if you create the SSL context by calling the SSLContext
constructor yourself, it will not have certificate validation nor hostname checking enabled by default. If you do so, please read the paragraphs below to achieve a good security level.
When calling the SSLContext
constructor directly, CERT_NONE
is the default. Since it does not authenticate the other peer, it can be insecure, especially in client mode where most of time you would like to ensure the authenticity of the server you're talking to. Therefore, when in client mode, it is highly recommended to use CERT_REQUIRED
. However, it is in itself not sufficient; you also have to check that the server certificate, which can be obtained by calling SSLSocket.getpeercert
, matches the desired service. For many protocols and applications, the service can be identified by the hostname; in this case, the match_hostname
function can be used. This common check is automatically performed when SSLContext.check_hostname
is enabled.
3.7 Hostname matchings is now performed by OpenSSL. Python no longer uses match_hostname
.
In server mode, if you want to authenticate your clients using the SSL layer (rather than using a higher-level authentication mechanism), you'll also have to specify CERT_REQUIRED
and similarly check the client certificate.
SSL versions 2 and 3 are considered insecure and are therefore dangerous to use. If you want maximum compatibility between clients and servers, it is recommended to use PROTOCOL_TLS_CLIENT
or PROTOCOL_TLS_SERVER
as the protocol version. SSLv2 and SSLv3 are disabled by default.
>>> client_context = ssl.SSLContext(ssl.PROTOCOL_TLS_CLIENT)
>>> client_context.minimum_version = ssl.TLSVersion.TLSv1_3
>>> client_context.maximum_version = ssl.TLSVersion.TLSv1_3
The SSL context created above will only allow TLSv1.2 and later (if supported by your system) connections to a server. PROTOCOL_TLS_CLIENT
implies certificate validation and hostname checks by default. You have to load certificates into the context.
If you have advanced security requirements, fine-tuning of the ciphers enabled when negotiating a SSL session is possible through the SSLContext.set_ciphers
method. Starting from Python 3.2.3, the ssl module disables certain weak ciphers by default, but you may want to further restrict the cipher choice. Be sure to read OpenSSL's documentation about the cipher list format. If you want to check which ciphers are enabled by a given cipher list, use SSLContext.get_ciphers
or the openssl ciphers
command on your system.
If using this module as part of a multi-processed application (using, for example the multiprocessing
or concurrent.futures
modules), be aware that OpenSSL's internal random number generator does not properly handle forked processes. Applications must change the PRNG state of the parent process if they use any SSL feature with os.fork
. Any successful call of ~ssl.RAND_add
, ~ssl.RAND_bytes
or ~ssl.RAND_pseudo_bytes
is sufficient.
3.7
The TLS 1.3 protocol behaves slightly differently than previous version of TLS/SSL. Some new TLS 1.3 features are not yet available.
- TLS 1.3 uses a disjunct set of cipher suites. All AES-GCM and ChaCha20 cipher suites are enabled by default. The method
SSLContext.set_ciphers
cannot enable or disable any TLS 1.3 ciphers yet, butSSLContext.get_ciphers
returns them. - Session tickets are no longer sent as part of the initial handshake and are handled differently.
SSLSocket.session
andSSLSession
are not compatible with TLS 1.3. - Client-side certificates are also no longer verified during the initial handshake. A server can request a certificate at any time. Clients process certificate requests while they send or receive application data from the server.
- TLS 1.3 features like early data, deferred TLS client cert request, signature algorithm configuration, and rekeying are not supported yet.
- Class
socket.socket
Documentation of underlying
socket
class- SSL/TLS Strong Encryption: An Introduction
Intro from the Apache HTTP Server documentation
RFC 1422: Privacy Enhancement for Internet Electronic Mail: Part II: Certificate-Based Key Management <1422>
Steve Kent
RFC 4086: Randomness Requirements for Security <4086>
Donald E., Jeffrey I. Schiller
RFC 5280: Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile <5280>
- Cooper
RFC 5246: The Transport Layer Security (TLS) Protocol Version 1.2 <5246>
- Dierks et. al.
RFC 6066: Transport Layer Security (TLS) Extensions <6066>
- Eastlake
- IANA TLS: Transport Layer Security (TLS) Parameters
IANA
RFC 7525: Recommendations for Secure Use of Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS) <7525>
IETF
- Mozilla's Server Side TLS recommendations
Mozilla