mirror of https://github.com/nucypher/pyUmbral.git
40 lines
1.3 KiB
Python
40 lines
1.3 KiB
Python
import os
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from cryptography.hazmat.primitives.ciphers.aead import ChaCha20Poly1305
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DEM_KEYSIZE = 32
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DEM_NONCE_SIZE = 12
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class UmbralDEM(object):
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def __init__(self, symm_key: bytes):
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"""
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Initializes an UmbralDEM object. Requires a key to perform
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ChaCha20-Poly1305.
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"""
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if len(symm_key) != DEM_KEYSIZE:
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raise ValueError(
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"Invalid key size, must be {} bytes".format(DEM_KEYSIZE)
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)
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self.cipher = ChaCha20Poly1305(symm_key)
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def encrypt(self, data: bytes, authenticated_data: bytes=None):
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"""
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Encrypts data using ChaCha20-Poly1305 with optional authenticated data.
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"""
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nonce = os.urandom(DEM_NONCE_SIZE)
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enc_data = self.cipher.encrypt(nonce, data, authenticated_data)
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# Ciphertext will be a 12 byte nonce, the ciphertext, and a 16 byte tag.
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return nonce + enc_data
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def decrypt(self, ciphertext: bytes, authenticated_data: bytes=None):
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"""
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Decrypts data using ChaCha20-Poly1305 and validates the provided
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authenticated data.
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"""
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nonce = ciphertext[:DEM_NONCE_SIZE]
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ciphertext = ciphertext[DEM_NONCE_SIZE:]
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cleartext = self.cipher.decrypt(nonce, ciphertext, authenticated_data)
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return cleartext
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