2.2. Digital Signatures

Digital signatures are implemented using the RSA cryptosystem. These types and functions are designed for signing purposes only (that is, not for encrypting data), as this signature cryptosystem is non-reversible. If you need to encrypt data, use Asymmetric Encryption.

2.2.1. Types

class SignatureVerifyKey

The RSA public key for signature verification.

class SignatureSignKey

The RSA private key for signature creation.

2.2.2. Functions

crypto.SignatureKeyGen() → Tuple[SignatureVerifyKey, SignatureSignKey]

Generates a public-key pair for asymmetric encryption purposes.

Returns:

A tuple corresponding to a SignatureVerifyKey and SignatureSignKey pair

Return type:

Tuple[SignatureVerifyKey, SignatureSignKey]

Example usage:

# Returns a tuple, so assign return values to two variables:
public_key, private_key = crypto.SignatureKeyGen()

crypto.SignatureSign(key: SignatureSignKey, message: bytes) → bytes

Returns a signature on message using the private key key.

message does not need to be hashed in advance of passing it to this function.

Parameters:

• key (SignatureSignKey) – The private key

• message (bytes) – The bytes to sign

Returns:

The resulting signature

Return type:

bytes

crypto.SignatureVerify(key: SignatureVerifyKey, message: bytes, signature: bytes) → bool

Uses the public key key to verify that signature is a valid signature for message.

Parameters:

• key (SignatureVerifyKey) – The public key to sign with

• message (bytes) – The message to verify

• signature (bytes) – The signature to verify

Returns:

True if verification succeeds; otherwise, False

Return type:

bool

2.2.3. Class Methods

Note

You probably don’t have to worry about the methods below if you’re just thinking about the design, but you’ll probably need to use them once you start implementing your client application.

These class methods are for the purposes of serialization (see Serialization API). Also, see Key Serialization Example for example usage.

classmethod crypto.SignatureVerifyKey.from_bytes(b: bytes) → SignatureVerifyKey

Converts a serialized bytes representation of a SignatureVerifyKey to an actual Python instance of SignatureVerifyKey.

Returns:

The deserialized SignatureVerifyKey instance

Return type:

SignatureVerifyKey

Raises:

ValueError – if b was not a valid encoding of a SignatureVerifyKey instance

classmethod crypto.SignatureSignKey.from_bytes(b: bytes) → SignatureSignKey

Converts a serialized bytes representation of a SignatureSignKey to an actual Python instance of SignatureSignKey.

Returns:

The deserialized SignatureSignKey instance

Return type:

SignatureSignKey

Raises:

ValueError – if b was not a valid encoding of a SignatureSignKey instance