Danger
This is a “Hazardous Materials” module. You should ONLY use it if you’re 100% absolutely sure that you know what you’re doing because this module is full of land mines, dragons, and dinosaurs with laser guns.
Key Serialization¶
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
rsa
,
dsa
, and
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 selfidentifying, 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. You
can load it using load_pem_x509_certificate()
and
extract the public key with
Certificate.public_key
.

cryptography.hazmat.primitives.serialization.
load_pem_private_key
(data, password, backend)[source]¶ New in version 0.6.
Deserialize a private key from PEM encoded data to one of the supported asymmetric private key types.
Parameters:  data (byteslike) – The PEM encoded key data.
 password – The password to use to decrypt the data. Should
be
None
if the private key is not encrypted.  backend – An instance of
PEMSerializationBackend
.
Returns: One of
RSAPrivateKey
,DSAPrivateKey
,DHPrivateKey
, orEllipticCurvePrivateKey
depending on the contents ofdata
.Raises:  ValueError – If the PEM data could not be decrypted or if its structure could not be decoded successfully.
 TypeError – If a
password
was given and the private key was not encrypted. Or if the key was encrypted but no password was supplied.  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.

cryptography.hazmat.primitives.serialization.
load_pem_public_key
(data, backend)[source]¶ New in version 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 RFC 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
Parameters:  data (bytes) – The PEM encoded key data.
 backend – An instance of
PEMSerializationBackend
.
Returns: One of
RSAPublicKey
,DSAPublicKey
,DHPublicKey
, orEllipticCurvePublicKey
depending on the contents ofdata
.Raises:  ValueError – If the PEM data’s structure could not be decoded successfully.
 cryptography.exceptions.UnsupportedAlgorithm – If the serialized key is of a type that is not supported by the backend.

cryptography.hazmat.primitives.serialization.
load_pem_parameters
(data, backend)[source]¶ New in version 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
Parameters:  data (bytes) – The PEM encoded parameters data.
 backend – An instance of
PEMSerializationBackend
.
Returns: Currently only
DHParameters
supported.Raises:  ValueError – If the PEM data’s structure could not be decoded successfully.
 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.

cryptography.hazmat.primitives.serialization.
load_der_private_key
(data, password, backend)[source]¶ New in version 0.8.
Deserialize a private key from DER encoded data to one of the supported asymmetric private key types.
Parameters:  data (byteslike) – The DER encoded key data.
 password (byteslike) – The password to use to decrypt the data. Should
be
None
if the private key is not encrypted.  backend – An instance of
DERSerializationBackend
.
Returns: One of
RSAPrivateKey
,DSAPrivateKey
,DHPrivateKey
, orEllipticCurvePrivateKey
depending on the contents ofdata
.Raises:  ValueError – If the DER data could not be decrypted or if its structure could not be decoded successfully.
 TypeError – If a
password
was given and the private key was not encrypted. Or if the key was encrypted but no password was supplied.  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

cryptography.hazmat.primitives.serialization.
load_der_public_key
(data, backend)[source]¶ New in version 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 RFC 5280.Parameters:  data (bytes) – The DER encoded key data.
 backend – An instance of
DERSerializationBackend
.
Returns: One of
RSAPublicKey
,DSAPublicKey
,DHPublicKey
, orEllipticCurvePublicKey
depending on the contents ofdata
.Raises:  ValueError – If the DER data’s structure could not be decoded successfully.
 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

cryptography.hazmat.primitives.serialization.
load_der_parameters
(data, backend)[source]¶ New in version 2.0.
Deserialize parameters from DER encoded data to one of the supported asymmetric parameters types.
Parameters:  data (bytes) – The DER encoded parameters data.
 backend – An instance of
DERSerializationBackend
.
Returns: Currently only
DHParameters
supported.Raises:  ValueError – If the DER data’s structure could not be decoded successfully.
 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 RFC 4253.
An example RSA key in OpenSSH format (line breaks added for formatting purposes):
sshrsa 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 sshdss
rather than
sshrsa
. ECDSA keys have a slightly different format, they begin with
ecdsasha2{curve}
.

cryptography.hazmat.primitives.serialization.
load_ssh_public_key
(data, backend)[source]¶ New in version 0.7.
Deserialize a public key from OpenSSH (RFC 4253) encoded data to an instance of the public key type for the specified backend.
Note
Currently Ed25519 keys are not supported.
Parameters:  data (bytes) – The OpenSSH encoded key data.
 backend – A backend which implements
RSABackend
,DSABackend
, orEllipticCurveBackend
depending on the key’s type.
Returns: One of
RSAPublicKey
,DSAPublicKey
, orEllipticCurvePublicKey
depending on the contents ofdata
.Raises:  ValueError – If the OpenSSH data could not be properly decoded or if the key is not in the proper format.
 cryptography.exceptions.UnsupportedAlgorithm – If the serialized key is of a type that is not supported.
PKCS12¶
PKCS12 is a binary format described in RFC 7292. It can contain
certificates, keys, and more. PKCS12 files commonly have a pfx
or p12
file suffix.
Note
cryptography
only supports a single private key and associated
certificates when parsing PKCS12 files at this time.

cryptography.hazmat.primitives.serialization.pkcs12.
load_key_and_certificates
(data, password, backend)[source]¶ New in version 2.5.
Deserialize a PKCS12 blob.
Parameters:  data (byteslike) – The binary data.
 password (byteslike) – The password to use to decrypt the data.
None
if the PKCS12 is not encrypted.  backend – A backend instance.
Returns: A tuple of
(private_key, certificate, additional_certificates)
.private_key
is a private key type orNone
,certificate
is either theCertificate
whose public key matches the private key in the PKCS 12 object orNone
, andadditional_certificates
is a list of all otherCertificate
instances in the PKCS12 object.
Serialization Formats¶

class
cryptography.hazmat.primitives.serialization.
PrivateFormat
[source]¶ New in version 0.8.
An enumeration for private key formats. Used with the
private_bytes
method available onRSAPrivateKeyWithSerialization
,EllipticCurvePrivateKeyWithSerialization
,DHPrivateKeyWithSerialization
andDSAPrivateKeyWithSerialization
.
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

Raw
¶ New in version 2.5.
A raw format used by X448 key exchange. It is a binary format and is invalid for other key types.


class
cryptography.hazmat.primitives.serialization.
PublicFormat
[source]¶ New in version 0.8.
An enumeration for public key formats. Used with the
public_bytes
method available onRSAPublicKeyWithSerialization
,EllipticCurvePublicKeyWithSerialization
,DHPublicKeyWithSerialization
, andDSAPublicKeyWithSerialization
.
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
¶ New in version 1.4.
The public key format used by OpenSSH (e.g. as found in
~/.ssh/id_rsa.pub
or~/.ssh/authorized_keys
).

Raw
¶ New in version 2.5.
A raw format used by X448 key exchange. It is a binary format and is invalid for other key types.

CompressedPoint
¶ New in version 2.5.
A compressed elliptic curve public key as defined in ANSI X9.62 section 4.3.6 (as well as SEC 1 v2.0).

UncompressedPoint
¶ New in version 2.5.
An uncompressed elliptic curve public key as defined in ANSI X9.62 section 4.3.6 (as well as SEC 1 v2.0).


class
cryptography.hazmat.primitives.serialization.
ParameterFormat
[source]¶ New in version 2.0.
An enumeration for parameters formats. Used with the
parameter_bytes
method available onDHParametersWithSerialization
.
Serialization Encodings¶

class
cryptography.hazmat.primitives.serialization.
Encoding
[source]¶ An enumeration for encoding types. Used with the
private_bytes
method available onRSAPrivateKeyWithSerialization
,EllipticCurvePrivateKeyWithSerialization
,DHPrivateKeyWithSerialization
,DSAPrivateKeyWithSerialization
, andX448PrivateKey
as well aspublic_bytes
onRSAPublicKey
,DHPublicKey
,EllipticCurvePublicKey
, andX448PublicKey
.
PEM
¶ New in version 0.8.
For PEM format. This is a base64 format with delimiters.

DER
¶ New in version 0.9.
For DER format. This is a binary format.

OpenSSH
¶ New in version 1.4.
The format used by OpenSSH public keys. This is a text format.

Raw
¶ New in version 2.5.
A raw format used by X448 key exchange. It is a binary format and is invalid for other key types.

X962
¶ New in version 2.5.
The format used by elliptic curve point encodings. This is a binary format.

Serialization Encryption Types¶

class
cryptography.hazmat.primitives.serialization.
KeySerializationEncryption
[source]¶ Objects with this interface are usable as encryption types with methods like
private_bytes
available onRSAPrivateKeyWithSerialization
,EllipticCurvePrivateKeyWithSerialization
,DHPrivateKeyWithSerialization
andDSAPrivateKeyWithSerialization
. All other classes in this section represent the available choices for encryption and have this interface. They are used withprivate_bytes
.

class
cryptography.hazmat.primitives.serialization.
BestAvailableEncryption
(password)[source]¶ 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.
Parameters: password (bytes) – The password to use for encryption.