lepture/authlib

"""
    authlib.jose.draft
    ~~~~~~~~~~~~~~~~~~~~

    Content Encryption per `Section 4`_.

    .. _`Section 4`: https://datatracker.ietf.org/doc/html/draft-amringer-jose-chacha-02#section-4
"""
from authlib.jose.rfc7516 import JWEEncAlgorithm
from Cryptodome.Cipher import ChaCha20_Poly1305 as Cryptodome_ChaCha20_Poly1305


class XC20PEncAlgorithm(JWEEncAlgorithm):
    # Use of an IV of size 192 bits is REQUIRED with this algorithm.
    # https://datatracker.ietf.org/doc/html/draft-amringer-jose-chacha-02#section-4.1
    IV_SIZE = 192

    def __init__(self, key_size):
        self.name = 'XC20P'
        self.description = 'XChaCha20-Poly1305'
        self.key_size = key_size
        self.CEK_SIZE = key_size

    def encrypt(self, msg, aad, iv, key):
        """Content Encryption with AEAD_XCHACHA20_POLY1305

        :param msg: text to be encrypt in bytes
        :param aad: additional authenticated data in bytes
        :param iv: initialization vector in bytes
        :param key: encrypted key in bytes
        :return: (ciphertext, tag)
        """
        self.check_iv(iv)
        chacha = Cryptodome_ChaCha20_Poly1305.new(key=key, nonce=iv)
        chacha.update(aad)
        ciphertext, tag = chacha.encrypt_and_digest(msg)
        return ciphertext, tag

    def decrypt(self, ciphertext, aad, iv, tag, key):
        """Content Decryption with AEAD_XCHACHA20_POLY1305

        :param ciphertext: ciphertext in bytes
        :param aad: additional authenticated data in bytes
        :param iv: initialization vector in bytes
        :param tag: authentication tag in bytes
        :param key: encrypted key in bytes
        :return: message
        """
        self.check_iv(iv)
        chacha = Cryptodome_ChaCha20_Poly1305.new(key=key, nonce=iv)
        chacha.update(aad)
        return chacha.decrypt_and_verify(ciphertext, tag)