serialization.rst

Key Serialization

cryptography.hazmat.primitives.serialization

import base64

pem_data = b""" -----BEGIN RSA PRIVATE KEY-----MIICXgIBAAKBgQDn09PV9KPE7Q+N5K5UtNLT1DLl8z/pKM2pP5tXqWx2OsEw00lC kDHdHESwzS050s/8rtkERKKyusCzCm9+vC1pQzUlmtibfF4PQAQc1pJL6KHqlidg Hw49atYmnC25CaeXt65pAYXoIacOZ8k5X7FW3Eagex8nG0iMw4ObOtg6CwIDAQAB AoGBAL31l/4YYN1rNrSZLrQgGyUSGsbLxJHEKolFon95R3O1fzoH117gkstQb4TE Cwv3jw/JIfBaYUq8tku/AE9D2Jx51x7kYaCuQIMTavKIgkXKfxTQCQDjSEfkvXMW 4WOIj5sYdSCNbzLbaeFsWG32bSsBTy/sSheDIlCEFnqDuqwBAkEA+wYfJEMDf5nS VCQd9VKGM4HVeTWBioaWBFCflFdhc1Vb65dsNDp8iIMZgAHC2LEX5dMUmgqXk7AT lwFlIeW4CwJBAOxsSfuIVMuPKyx1xQ6ebpC7zeVxIOdswcM8ain91MSGDdKZw6pF ioFh3kUbKHw4yqqHbdRmUDAJ1mcgGJQOxgECQQCmQaGylKfmhWymyd0FtIip6J4I z4ViyEznwrZOu6kRiEF/QiUqWmpMx/fFrmTsvC5Fy43jkIxgBsiSxRvEXa+NAkB+ 5m0bhwTEslchKSGZhC6inzuYAQ4BSh4C1mXBnk5bIf0/Ymtk9KiwY8CzZS1o5+7Y c5LfI/+8mTss5UxsBDYBAkEA6NqhcsNWndIJZiWUU4u+RjFUQXqH8WCyJmEDCNxs 7SGRS1DTUGX4Y70m9dQpguy6Zg+gpHC+o+ERZR06uEQr+w== -----END RSA PRIVATE KEY-----""".strip() public_pem_data = b""" -----BEGIN PUBLIC KEY-----MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDn09PV9KPE7Q+N5K5UtNLT1DLl 8z/pKM2pP5tXqWx2OsEw00lCkDHdHESwzS050s/8rtkERKKyusCzCm9+vC1pQzUl mtibfF4PQAQc1pJL6KHqlidgHw49atYmnC25CaeXt65pAYXoIacOZ8k5X7FW3Eag ex8nG0iMw4ObOtg6CwIDAQAB -----END PUBLIC KEY-----""".strip() der_data = base64.b64decode( b"MIICdwIBADANBgkqhkiG9w0BAQEFAASCAmEwggJdAgEAAoGBALskegl+DrI3Msw5Z63x" b"nj1rgoPR0KykwBi+jZgAwHv/B0TJyhy6NuEnaf+x442L7lepOqoWQzlUGXyuaSQU9mT/" b"vHTGZ2xM8QJJaccr4eGho0MU9HePyNCFWjWVrGKpwSEAd6CLlzC0Wiy4kC9IoAUoS/IP" b"jeyLTQNCddatgcARAgMBAAECgYAA/LlKJgeJUStTcpHgGD6mXjHvnAwWJELQKDP5+tA8" b"VAQGwBX1G5qzJDGrPGtHQ7DSqdwF4YFZtgTpZmGq1wsAjz3lv6L4XiVsHiIPtP1B4gMx" b"X9ogxcDzVQ7hyezXPioMAcp7Isus9Csn8HhftcL56BRabn6GvWqbIAy6zJcgEQJBAMlZ" b"nymKW5/jKth+wkCfqEXlPhGNPO1uq87QZUbYxwdjtSM09J9+HMfH+WXR9ARCOL46DJ0I" b"JfyjcdmuDDlh9IkCQQDt76up1Tmc7lkb/89IRBu2MudGJPMEf96VCG11nmcXulyk1OLi" b"TXfO62YpxZbgYrvlrNxEYlSG7WQMztBgA51JAkBU2RhyJ+S+drsaaigvlVgSxCyotszi" b"/Q0XZMgY18bfPUwanvkqsLkuEv3sw1HB7an9t3aTQdjIIpQad/acw8OJAkEAjvmnCK21" b"KgTbjQShtQYgNNLPwImxcjG4OYvP4o6l2k9FHlNCZsQwSymOwWkXKYyK5g+CaKFBs7Zw" b"mXWpJxjk6QJBAInqbm1w3yVfGD9I2mMQi/6oDJQP3pdWU4mU4h4sdDyRgTQLpkD4yypg" b"jOACt4mTzxifSVT9fT+a79SkT8FFmZE=" ) public_der_data = base64.b64decode( b"MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQC7JHoJfg6yNzLMOWet8Z49a4KD0dCs" b"pMAYvo2YAMB7/wdEycocujbhJ2n/seONi+5XqTqqFkM5VBl8rmkkFPZk/7x0xmdsTPEC" b"SWnHK+HhoaNDFPR3j8jQhVo1laxiqcEhAHegi5cwtFosuJAvSKAFKEvyD43si00DQnXW" b"rYHAEQIDAQAB" ) message = b""

def sign_with_rsa_key(key, message):

return b""

def sign_with_dsa_key(key, message):

return b""

parameters_pem_data = b""" -----BEGIN DH PARAMETERS-----MIGHAoGBALsrWt44U1ojqTy88o0wfjysBE51V6Vtarjm2+5BslQK/RtlndHde3gx +ccNs+InANszcuJFI8AHt4743kGRzy5XSlul4q4dDJENOHoyqYxueFuFVJELEwLQ XrX/McKw+hS6GPVQnw6tZhgGo9apdNdYgeLQeQded8Bum8jqzP3rAgEC -----END DH PARAMETERS-----""".strip()

parameters_der_data = base64.b64decode(

b"MIGHAoGBALsrWt44U1ojqTy88o0wfjysBE51V6Vtarjm2+5BslQK/RtlndHde3gx+ccNs+In" b"ANszncuJFI8AHt4743kGRzy5XSlul4q4dDJENOHoyqYxueFuFVJELEwLQXrX/McKw+hS6GP" b"VQnw6tZhgGno9apdNdYgeLQeQded8Bum8jqzP3rAgEC"

)

There are several common schemes for serializing asymmetric private and public keys to bytes. They generally support encryption of private keys and additional key metadata.

Many serialization formats support multiple different types of asymmetric keys and will return an instance of the appropriate type. You should check that the returned key matches the type your application expects when using these methods.

>>> from cryptography.hazmat.backends import default_backend >>> from cryptography.hazmat.primitives.asymmetric import dsa, rsa >>> from cryptography.hazmat.primitives.serialization import load_pem_private_key >>> key = load_pem_private_key(pem_data, password=None, backend=default_backend()) >>> if isinstance(key, rsa.RSAPrivateKey): ... signature = sign_with_rsa_key(key, message) ... elif isinstance(key, dsa.DSAPrivateKey): ... signature = sign_with_dsa_key(key, message) ... else: ... raise TypeError

Key dumping

The serialization module contains functions for loading keys from bytes. To dump a key object to bytes, you must call the appropriate method on the key object. Documentation for these methods in found in the ~cryptography.hazmat.primitives.asymmetric.rsa, ~cryptography.hazmat.primitives.asymmetric.dsa, and ~cryptography.hazmat.primitives.asymmetric.ec module documentation.

PEM

PEM is an encapsulation format, meaning keys in it can actually be any of several different key types. However these are all self-identifying, so you don't need to worry about this detail. PEM keys are recognizable because they all begin with -----BEGIN {format}----- and end with -----END {format}-----.

Note

A PEM block which starts with -----BEGIN CERTIFICATE----- is not a public or private key, it's an X.509 Certificate </x509/index>. You can load it using ~cryptography.x509.load_pem_x509_certificate and extract the public key with Certificate.public_key <cryptography.x509.Certificate.public_key>.

load_pem_private_key(data, password, backend)

0.6

Deserialize a private key from PEM encoded data to one of the supported asymmetric private key types.

param bytes data

The PEM encoded key data.

param bytes password

The password to use to decrypt the data. Should be None if the private key is not encrypted.

param backend

An instance of ~cryptography.hazmat.backends.interfaces.PEMSerializationBackend.

returns

One of ~cryptography.hazmat.primitives.asymmetric.rsa.RSAPrivateKey, ~cryptography.hazmat.primitives.asymmetric.dsa.DSAPrivateKey, ~cryptography.hazmat.primitives.asymmetric.dh.DHPrivateKey, or ~cryptography.hazmat.primitives.asymmetric.ec.EllipticCurvePrivateKey depending on the contents of data.

raises ValueError

If the PEM data could not be decrypted or if its structure could not be decoded successfully.

raises TypeError

If a password was given and the private key was not encrypted. Or if the key was encrypted but no password was supplied.

raises cryptography.exceptions.UnsupportedAlgorithm

If the serialized key is of a type that is not supported by the backend or if the key is encrypted with a symmetric cipher that is not supported by the backend.

load_pem_public_key(data, backend)

0.6

Deserialize a public key from PEM encoded data to one of the supported asymmetric public key types. The PEM encoded data is typically a subjectPublicKeyInfo payload as specified in 5280.

>>> from cryptography.hazmat.primitives.serialization import load_pem_public_key >>> key = load_pem_public_key(public_pem_data, backend=default_backend()) >>> isinstance(key, rsa.RSAPublicKey) True

param bytes data

The PEM encoded key data.

param backend

An instance of ~cryptography.hazmat.backends.interfaces.PEMSerializationBackend.

returns

One of ~cryptography.hazmat.primitives.asymmetric.rsa.RSAPublicKey, ~cryptography.hazmat.primitives.asymmetric.dsa.DSAPublicKey, ~cryptography.hazmat.primitives.asymmetric.dh.DHPublicKey, or ~cryptography.hazmat.primitives.asymmetric.ec.EllipticCurvePublicKey depending on the contents of data.

raises ValueError

If the PEM data's structure could not be decoded successfully.

raises cryptography.exceptions.UnsupportedAlgorithm

If the serialized key is of a type that is not supported by the backend.

load_pem_parameters(data, backend)

2.0

Deserialize parameters from PEM encoded data to one of the supported asymmetric parameters types.

>>> from cryptography.hazmat.primitives.serialization import load_pem_parameters >>> from cryptography.hazmat.primitives.asymmetric import dh >>> parameters = load_pem_parameters(parameters_pem_data, backend=default_backend()) >>> isinstance(parameters, dh.DHParameters) True

param bytes data

The PEM encoded parameters data.

param backend

An instance of ~cryptography.hazmat.backends.interfaces.PEMSerializationBackend.

returns

Currently only ~cryptography.hazmat.primitives.asymmetric.dh.DHParameters supported.

raises ValueError

If the PEM data's structure could not be decoded successfully.

raises cryptography.exceptions.UnsupportedAlgorithm

If the serialized parameters is of a type that is not supported by the backend.

DER

DER is an ASN.1 encoding type. There are no encapsulation boundaries and the data is binary. DER keys may be in a variety of formats, but as long as you know whether it is a public or private key the loading functions will handle the rest.

load_der_private_key(data, password, backend)

0.8

Deserialize a private key from DER encoded data to one of the supported asymmetric private key types.

param bytes data

The DER encoded key data.

param bytes password

The password to use to decrypt the data. Should be None if the private key is not encrypted.

param backend

An instance of ~cryptography.hazmat.backends.interfaces.DERSerializationBackend.

returns

One of ~cryptography.hazmat.primitives.asymmetric.rsa.RSAPrivateKey, ~cryptography.hazmat.primitives.asymmetric.dsa.DSAPrivateKey, ~cryptography.hazmat.primitives.asymmetric.dh.DHPrivateKey, or ~cryptography.hazmat.primitives.asymmetric.ec.EllipticCurvePrivateKey depending on the contents of data.

raises ValueError

If the DER data could not be decrypted or if its structure could not be decoded successfully.

raises TypeError

If a password was given and the private key was not encrypted. Or if the key was encrypted but no password was supplied.

raises cryptography.exceptions.UnsupportedAlgorithm

If the serialized key is of a type that is not supported by the backend or if the key is encrypted with a symmetric cipher that is not supported by the backend.

>>> from cryptography.hazmat.backends import default_backend >>> from cryptography.hazmat.primitives.asymmetric import rsa >>> from cryptography.hazmat.primitives.serialization import load_der_private_key >>> key = load_der_private_key(der_data, password=None, backend=default_backend()) >>> isinstance(key, rsa.RSAPrivateKey) True

load_der_public_key(data, backend)

0.8

Deserialize a public key from DER encoded data to one of the supported asymmetric public key types. The DER encoded data is typically a subjectPublicKeyInfo payload as specified in 5280.

param bytes data

The DER encoded key data.

param backend

An instance of ~cryptography.hazmat.backends.interfaces.DERSerializationBackend.

returns

One of ~cryptography.hazmat.primitives.asymmetric.rsa.RSAPublicKey, ~cryptography.hazmat.primitives.asymmetric.dsa.DSAPublicKey, ~cryptography.hazmat.primitives.asymmetric.dh.DHPublicKey, or ~cryptography.hazmat.primitives.asymmetric.ec.EllipticCurvePublicKey depending on the contents of data.

raises ValueError

If the DER data's structure could not be decoded successfully.

raises cryptography.exceptions.UnsupportedAlgorithm

If the serialized key is of a type that is not supported by the backend.

>>> from cryptography.hazmat.backends import default_backend >>> from cryptography.hazmat.primitives.asymmetric import rsa >>> from cryptography.hazmat.primitives.serialization import load_der_public_key >>> key = load_der_public_key(public_der_data, backend=default_backend()) >>> isinstance(key, rsa.RSAPublicKey) True

load_der_parameters(data, backend)

2.0

Deserialize parameters from DER encoded data to one of the supported asymmetric parameters types.

param bytes data

The DER encoded parameters data.

param backend

An instance of ~cryptography.hazmat.backends.interfaces.DERSerializationBackend.

returns

Currently only ~cryptography.hazmat.primitives.asymmetric.dh.DHParameters supported.

raises ValueError

If the DER data's structure could not be decoded successfully.

raises cryptography.exceptions.UnsupportedAlgorithm

If the serialized key is of a type that is not supported by the backend.

>>> from cryptography.hazmat.backends import default_backend >>> from cryptography.hazmat.primitives.asymmetric import dh >>> from cryptography.hazmat.primitives.serialization import load_der_parameters >>> parameters = load_der_parameters(parameters_der_data, backend=default_backend()) >>> isinstance(parameters, dh.DHParameters) True

OpenSSH Public Key

The format used by OpenSSH to store public keys, as specified in 4253.

An example RSA key in OpenSSH format (line breaks added for formatting purposes):

ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQDDu/XRP1kyK6Cgt36gts9XAk
FiiuJLW6RU0j3KKVZSs1I7Z3UmU9/9aVh/rZV43WQG8jaR6kkcP4stOR0DEtll
PDA7ZRBnrfiHpSQYQ874AZaAoIjgkv7DBfsE6gcDQLub0PFjWyrYQUJhtOLQEK
vY/G0vt2iRL3juawWmCFdTK3W3XvwAdgGk71i6lHt+deOPNEPN2H58E4odrZ2f
sxn/adpDqfb2sM0kPwQs0aWvrrKGvUaustkivQE4XWiSFnB0oJB/lKK/CKVKuy
///ImSCGHQRvhwariN2tvZ6CBNSLh3iQgeB0AkyJlng7MXB2qYq/Ci2FUOryCX
2MzHvnbv testkey@localhost

DSA keys look almost identical but begin with ssh-dss rather than ssh-rsa. ECDSA keys have a slightly different format, they begin with ecdsa-sha2-{curve}.

load_ssh_public_key(data, backend)

0.7

Deserialize a public key from OpenSSH (4253) encoded data to an instance of the public key type for the specified backend.

Note

Currently Ed25519 keys are not supported.

param bytes data

The OpenSSH encoded key data.

param backend

A backend which implements ~cryptography.hazmat.backends.interfaces.RSABackend, ~cryptography.hazmat.backends.interfaces.DSABackend, or ~cryptography.hazmat.backends.interfaces.EllipticCurveBackend depending on the key's type.

returns

One of ~cryptography.hazmat.primitives.asymmetric.rsa.RSAPublicKey, ~cryptography.hazmat.primitives.asymmetric.dsa.DSAPublicKey, or ~cryptography.hazmat.primitives.asymmetric.ec.EllipticCurvePublicKey depending on the contents of data.

raises ValueError

If the OpenSSH data could not be properly decoded or if the key is not in the proper format.

raises cryptography.exceptions.UnsupportedAlgorithm

If the serialized key is of a type that is not supported.

Serialization Formats

0.8

An enumeration for private key formats. Used with the private_bytes method available on ~cryptography.hazmat.primitives.asymmetric.rsa.RSAPrivateKeyWithSerialization , ~cryptography.hazmat.primitives.asymmetric.ec.EllipticCurvePrivateKeyWithSerialization , ~cryptography.hazmat.primitives.asymmetric.dh.DHPrivateKeyWithSerialization and ~cryptography.hazmat.primitives.asymmetric.dsa.DSAPrivateKeyWithSerialization.

TraditionalOpenSSL

Frequently known as PKCS#1 format. Still a widely used format, but generally considered legacy.

A PEM encoded RSA key will look like:

-----BEGIN RSA PRIVATE KEY-----
...
-----END RSA PRIVATE KEY-----

PKCS8

A more modern format for serializing keys which allows for better encryption. Choose this unless you have explicit legacy compatibility requirements.

A PEM encoded key will look like:

-----BEGIN PRIVATE KEY-----
...
-----END PRIVATE KEY-----

0.8

An enumeration for public key formats. Used with the public_bytes method available on ~cryptography.hazmat.primitives.asymmetric.rsa.RSAPublicKeyWithSerialization , ~cryptography.hazmat.primitives.asymmetric.ec.EllipticCurvePublicKeyWithSerialization , ~cryptography.hazmat.primitives.asymmetric.dh.DHPublicKeyWithSerialization , and ~cryptography.hazmat.primitives.asymmetric.dsa.DSAPublicKeyWithSerialization.

SubjectPublicKeyInfo

This is the typical public key format. It consists of an algorithm identifier and the public key as a bit string. Choose this unless you have specific needs.

A PEM encoded key will look like:

-----BEGIN PUBLIC KEY-----
...
-----END PUBLIC KEY-----

PKCS1

Just the public key elements (without the algorithm identifier). This format is RSA only, but is used by some older systems.

A PEM encoded key will look like:

-----BEGIN RSA PUBLIC KEY-----
...
-----END RSA PUBLIC KEY-----

OpenSSH

1.4

The public key format used by OpenSSH (e.g. as found in ~/.ssh/id_rsa.pub or ~/.ssh/authorized_keys).

2.0

An enumeration for parameters formats. Used with the parameter_bytes method available on ~cryptography.hazmat.primitives.asymmetric.dh.DHParametersWithSerialization.

PKCS3

ASN1 DH parameters sequence as defined in PKCS3.

Serialization Encodings

An enumeration for encoding types. Used with the private_bytes method available on ~cryptography.hazmat.primitives.asymmetric.rsa.RSAPrivateKeyWithSerialization , ~cryptography.hazmat.primitives.asymmetric.ec.EllipticCurvePrivateKeyWithSerialization , ~cryptography.hazmat.primitives.asymmetric.dh.DHPrivateKeyWithSerialization and ~cryptography.hazmat.primitives.asymmetric.dsa.DSAPrivateKeyWithSerialization as well as public_bytes on ~cryptography.hazmat.primitives.asymmetric.rsa.RSAPublicKeyWithSerialization, ~cryptography.hazmat.primitives.asymmetric.dh.DHPublicKeyWithSerialization and ~cryptography.hazmat.primitives.asymmetric.ec.EllipticCurvePublicKeyWithSerialization.

PEM

0.8

For PEM format. This is a base64 format with delimiters.

DER

0.9

For DER format. This is a binary format.

OpenSSH

1.4

The format used by OpenSSH public keys. This is a text format.

Serialization Encryption Types

Objects with this interface are usable as encryption types with methods like private_bytes available on ~cryptography.hazmat.primitives.asymmetric.rsa.RSAPrivateKeyWithSerialization , ~cryptography.hazmat.primitives.asymmetric.ec.EllipticCurvePrivateKeyWithSerialization , ~cryptography.hazmat.primitives.asymmetric.dh.DHPrivateKeyWithSerialization and ~cryptography.hazmat.primitives.asymmetric.dsa.DSAPrivateKeyWithSerialization. All other classes in this section represent the available choices for encryption and have this interface. They are used with ~cryptography.hazmat.primitives.asymmetric.rsa.RSAPrivateKeyWithSerialization.private_bytes.

Encrypt using the best available encryption for a given key's backend. This is a curated encryption choice and the algorithm may change over time.

param bytes password

The password to use for encryption.

Do not encrypt.