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