Cryptography

The Delta Crypto package provides functionality for client-side cryptography.

covata.delta.crypto.generate_private_key()

Generates a RSAPrivateKey object. The public key object can be extracted by calling public_key() method on the generated key object.

Returns:the generated private key object Return type:RSAPrivateKey

covata.delta.crypto.serialize_public_key(public_key)

Serializes the provided public key object as base-64-encoded DER format using X.509 SubjectPublicKeyInfo with PKCS1.

Parameters:public_key (RSAPublicKey) – the public key object Returns:the key as base64 encoded unicode string Return type:str

covata.delta.crypto.calculate_sha256hex(payload)

Calculates the SHA256 hex digest of the given payload.

Parameters:payload (str) – the payload to be calculated Returns:SHA256 hex digest Return type:bytes

covata.delta.crypto.generate_secret_key()

Generates a 256 bits secret key.

Uses /dev/urandom on UNIX platforms, and CryptGenRandom on Windows.

Returns:the 256 bits secret key Return type:bytes

covata.delta.crypto.generate_initialisation_vector()

Generates a 128 bits initialisation vector.

Uses /dev/urandom on UNIX platforms, and CryptGenRandom on Windows.

Returns:the 128 bits initialisation vector Return type:bytes

covata.delta.crypto.encrypt(data, secret_key, initialisation_vector)

Encrypts data using the given secret key and initialisation vector.

Parameters:

• data (bytes) – the plaintext bytes to be encrypted
• secret_key (bytes) – the key to be used for encryption
• initialisation_vector (bytes) – the initialisation vector

Returns:

the cipher text and GCM authentication tag tuple

Return type:

(bytes, bytes)

covata.delta.crypto.decrypt(ciphertext, tag, secret_key, initialisation_vector)

Decrypts a cipher text using the given GCM authentication tag, secret key and initialisation vector.

Parameters:

• ciphertext (bytes) – the cipher text to be decrypted
• tag (bytes) – the GCM authentication tag
• secret_key (bytes) – the key to be used for encryption
• initialisation_vector (bytes) – the initialisation vector

Returns:

the decrypted plaintext

Return type:

bytes

covata.delta.crypto.encrypt_key_with_public_key(secret_key, public_encryption_key)

Encrypts the given secret key with the public key.

Parameters:

• secret_key (bytes) – the key to encrypt
• public_encryption_key (RSAPublicKey) – the public encryption key

Returns:

the encrypted key

Return type:

bytes

covata.delta.crypto.decrypt_with_private_key(secret_key, private_encryption_key)

Decrypts the given secret key with the private key.

Parameters:

• secret_key (bytes) – the secret key to decrypt
• private_encryption_key (RSAPrivateKey) – the private encryption key

Returns:

the decrypted key

Return type:

bytes

covata.delta.crypto.deserialize_public_key(b64_encoded_public_key)

loads a RSAPublicKey object from a serialized public key.

Parameters:b64_encoded_public_key (str) – the key as base64 encoded string Returns:the public key object Return type:RSAPublicKey