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, TLSv1.1 and TLSv1.2 come with openssl version 1.0.1.
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.
3.6
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.
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.
The following function allows for standalone socket creation. Starting from Python 3.2, it can be more flexible to use SSLContext.wrap_socket instead.
wrap_socket(sock, keyfile=None, certfile=None, server_side=False, cert_reqs=CERT_NONE, ssl_version={see docs}, 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.
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. wrap_socket may raise SSLError.
The keyfile and certfile parameters specify optional files which contain a certificate to be used to identify the local side of the connection. See the discussion of ssl-certificates for more information on how the certificate is stored in the certfile.
The parameter server_side is a boolean which identifies whether server-side or client-side behavior is desired from this socket.
The parameter cert_reqs specifies whether a certificate is required from the other side of the connection, and whether it will be validated if provided. It must be one of the three values CERT_NONE (certificates ignored), CERT_OPTIONAL (not required, but validated if provided), or CERT_REQUIRED (required and validated). If the value of this parameter is not CERT_NONE, then the ca_certs parameter must point to a file of CA certificates.
The ca_certs file contains a set of concatenated "certification authority" certificates, which are used to validate certificates passed from the other end of the connection. See the discussion of ssl-certificates for more information about how to arrange the certificates in this file.
The parameter ssl_version 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
Note
Which connections succeed will vary depending on the version of OpenSSL. For example, before OpenSSL 1.0.0, an SSLv23 client would always attempt SSLv2 connections.
The ciphers parameter sets the available ciphers for this SSL object. It should be a string in the OpenSSL cipher list format.
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.
3.2 New optional argument ciphers.
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, 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.
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.
3.7
TLS 1.3 cipher suites TLS_AES_128_GCM_SHA256, TLS_AES_256_GCM_SHA384, and TLS_CHACHA20_POLY1305_SHA256 were added to the default cipher string.
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 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_egd(path)
If you are running an entropy-gathering daemon (EGD) somewhere, and path is the pathname of a socket connection open to it, this will read 256 bytes of randomness from the socket, and add it to the SSL pseudo-random number generator to increase the security of generated secret keys. This is typically only necessary on systems without better sources of randomness.
See http://egd.sourceforge.net/ or http://prngd.sourceforge.net/ for sources of entropy-gathering daemons.
Availability: not available with LibreSSL and OpenSSL > 1.1.0
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, ca_certs=None)
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 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.
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.
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 orNoneif the file doesn't exist,capath- resolved path to capath orNoneif 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
Availability: 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)]Availability: 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.
Availability: Windows.
3.4
All constants are now
enum.IntEnumorenum.IntFlagcollections.3.6
CERT_NONE
Possible value for SSLContext.verify_mode, or the cert_reqs parameter to wrap_socket. In this mode (the default), no certificates will be required from the other side of the socket connection. If a certificate is received from the other end, no attempt to validate it is made.
See the discussion of ssl-security below.
CERT_OPTIONAL
Possible value for SSLContext.verify_mode, or the cert_reqs parameter to wrap_socket. In this mode no certificates will be required from the other side of the socket connection; but if they are provided, validation will be attempted and an SSLError will be raised on failure.
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.
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 check but non 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 has been loaded 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_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
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
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 data:`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 with flags like OP_NO_SSLv3 instead.
PROTOCOL_TLSv1
Selects TLS version 1.0 as the channel encryption protocol.
3.6
OpenSSL has deprecated all version specific protocols. Use the default protocol PROTOCOL_TLS with flags like OP_NO_SSLv3 instead.
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. Use the default protocol PROTOCOL_TLS with flags like OP_NO_SSLv3 instead.
PROTOCOL_TLSv1_2
Selects TLS version 1.2 as the channel encryption protocol. This is the most modern version, and probably the best choice for maximum protection, if both sides can speak it. Available only with openssl version 1.0.1+.
3.4
3.6
OpenSSL has deprecated all version specific protocols. Use the default protocol PROTOCOL_TLS with flags like OP_NO_SSLv3 instead.
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
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
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
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
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_NO_COMPRESSION
Disable compression on the SSL channel. This is useful if the application protocol supports its own compression scheme.
This option is only available with OpenSSL 1.0.0 and later.
3.3
enum.IntFlag collection of OP* constants.
OP_NO_TICKET
Prevent client side from requesting a session ticket.
3.6
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 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 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_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
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-zeroflagsargument is not allowed)~socket.socket.send(),~socket.socket.sendall()(with the same limitation)~socket.socket.sendfile()(butos.sendfilewill 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>.
Usually, SSLSocket are not created directly, but 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.
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
getpeercertwill returnNoneif you usedCERT_NONE(rather thanCERT_OPTIONALorCERT_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.
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
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.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 top-level 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. PROTOCOL_TLS is currently recommended for maximum interoperability and default value.
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).
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() # OpenSSL 1.0.x
[{'alg_bits': 256,
'description': 'ECDHE-RSA-AES256-GCM-SHA384 TLSv1.2 Kx=ECDH Au=RSA '
'Enc=AESGCM(256) Mac=AEAD',
'id': 50380848,
'name': 'ECDHE-RSA-AES256-GCM-SHA384',
'protocol': 'TLSv1/SSLv3',
'strength_bits': 256},
{'alg_bits': 128,
'description': 'ECDHE-RSA-AES128-GCM-SHA256 TLSv1.2 Kx=ECDH Au=RSA '
'Enc=AESGCM(128) Mac=AEAD',
'id': 50380847,
'name': 'ECDHE-RSA-AES128-GCM-SHA256',
'protocol': 'TLSv1/SSLv3',
'strength_bits': 128}]On OpenSSL 1.1 and newer the cipher dict contains additional fields:
>>> ctx.get_ciphers() # OpenSSL 1.1+
[{'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'}]Availability: OpenSSL 1.0.2+
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.
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.
OpenSSL 1.1.0 to 1.1.0e will abort the handshake and raise SSLError when both sides support ALPN but cannot agree on a protocol. 1.1.0f+ behaves like 1.0.2, SSLSocket.selected_alpn_protocol returns None.
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
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-Helman (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). sock must be a ~socket.SOCK_STREAM socket; other socket types are unsupported.
The returned SSL socket is tied to the context, its settings and certificates. The parameters server_side, do_handshake_on_connect and suppress_ragged_eofs have the same meaning as in the top-level wrap_socket function.
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.
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_sockets, 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 attr: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 with match_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.
Example:
import socket, ssl
context = ssl.SSLContext()
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.
Note
This features requires OpenSSL 0.9.8f or newer.
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.
Note
With versions of OpenSSL older than 0.9.8m, it is only possible to set options, not to clear them. Attempting to clear an option (by resetting the corresponding bits) will raise a ValueError.
3.6 SSLContext.options returns Options flags:
>>> ssl.create_default_context().options # doctest: +SKIP <Options.OP_ALLOP_NO_SSLv2|OP_NO_COMPRESSION: 2197947391>
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
Note
Only writeable with OpenSSL 1.1.0 or higher.
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). Available only with openssl version 0.9.8+.
3.4
3.6 SSLContext.verify_flags returns VerifyFlags flags:
>>> ssl.create_default_context().verify_flags # doctest: +SKIP <VerifyFlags.VERIFY_X509_TRUSTED_FIRST: 32768>
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 <VerifyMode.CERT_REQUIRED: 2>
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 he claims 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 supportThis 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()
>>> context.verify_mode = ssl.CERT_REQUIRED
>>> context.check_hostname = True
>>> 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)
When you use the context to connect to a server, CERT_REQUIRED validates the server certificate: it ensures that the server certificate was signed with one of the CA certificates, and checks the signature for correctness:
>>> 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.python.org'),
('DNS', 'docs.python.org'),
('DNS', 'testpypi.python.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 clientAnd 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
SSLSocketmethods will raise eitherSSLWantWriteErrororSSLWantReadErrorinstead ofBlockingIOErrorif an I/O operation would block.SSLWantReadErrorwill be raised if a read operation on the underlying socket is necessary, andSSLWantWriteErrorfor 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.sendmethod returned zero instead of raisingSSLWantWriteErrororSSLWantReadError.- Calling
~select.selecttells 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.recvandSSLSocket.sendfailures, 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.selectbeing aware of it. Therefore, you should first callSSLSocket.recvto drain any potentially available data, and then only block on a~select.selectcall if still necessary.(of course, similar provisions apply when using other primitives such as
~select.poll, or those in theselectorsmodule)The SSL handshake itself will be non-blocking: the
SSLSocket.do_handshakemethod has to be retried until it returns successfully. Here is a synopsis using~select.selectto 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.
An SSLObject instance can 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_npn_protocol~SSLSocket.cipher~SSLSocket.shared_ciphers~SSLSocket.compression~SSLSocket.pending~SSLSocket.do_handshake~SSLSocket.unwrap~SSLSocket.get_channel_binding
When compared to SSLSocket, this object lacks the following features:
- Any form of network IO;
recv()andsend()read and write only to the underlyingMemoryBIObuffers. - There is no do_handshake_on_connect machinery. You must always manually call
~SSLSocket.do_handshaketo 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
SSLEOFErrorexception. - The method
~SSLSocket.unwrapcall 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_callbackwill get anSSLObjectinstance instead of aSSLSocketinstance as its first parameter.
Some notes related to the use of SSLObject:
- All IO on an
SSLObjectisnon-blocking <ssl-nonblocking>. This means that for example~SSLSocket.readwill raise anSSLWantReadErrorif 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. AnSSLObjectis always created via anSSLContext.
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.
Note
In client mode,
CERT_OPTIONALandCERT_REQUIREDare equivalent unless anonymous ciphers are enabled (they are disabled by default).
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.options |= ssl.OP_NO_TLSv1
>>> client_context.options |= ssl.OP_NO_TLSv1_1The 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.
- Class
socket.socket Documentation of underlying
socketclass- SSL/TLS Strong Encryption: An Introduction
Intro from the Apache webserver documentation
- RFC 1422: Privacy Enhancement for Internet Electronic Mail: Part II: Certificate-Based Key Management
Steve Kent
- RFC 4086: Randomness Requirements for Security
Donald E., Jeffrey I. Schiller
- RFC 5280: Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile
- Cooper
- RFC 5246: The Transport Layer Security (TLS) Protocol Version 1.2
- Dierks et. al.
- RFC 6066: Transport Layer Security (TLS) Extensions
- 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)
IETF
- Mozilla's Server Side TLS recommendations
Mozilla