49 lines
1.9 KiB
Python
49 lines
1.9 KiB
Python
import secrets
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import chacha20
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import poly1305
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def unleu64(n):
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assert n >> 64 == 0
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return bytes((n >> i) & 0xff for i in range(0, 64, 8))
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def pad16(x):
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if len(x) % 16 == 0:
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return b''
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else:
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return b'\x00' * (16 - (len(x) % 16))
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def poly1305_key_gen(key, nonce):
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return chacha20.chacha20_block(key, 0, nonce)[:32]
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def generate_tag(aad, key, nonce, ciphertext):
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key = poly1305_key_gen(key, nonce)
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message = b''.join((
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aad, pad16(aad),
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ciphertext, pad16(ciphertext),
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unleu64(len(aad)),
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unleu64(len(ciphertext))
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))
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return poly1305.poly1305(message, key)
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def chapoly_aead_enc(aad, key, nonce, plaintext):
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ciphertext = bytes(chacha20.chacha20(key, 1, nonce, plaintext))
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tag = generate_tag(aad, key, nonce, ciphertext)
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return ciphertext + tag
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def chapoly_aead_dec(aad, key, nonce, ciphertext):
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ciphertext, tag = ciphertext[:-16], ciphertext[-16:]
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expected_tag = generate_tag(aad, key, nonce, ciphertext)
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if not secrets.compare_digest(tag, expected_tag):
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return None
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return bytes(chacha20.chacha20(key, 1, nonce, ciphertext))
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if __name__ == '__main__':
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plaintext = b"Ladies and Gentlemen of the class of '99: If I could offer you only one tip for the future, sunscreen would be it."
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aad = bytes.fromhex('50 51 52 53 c0 c1 c2 c3 c4 c5 c6 c7')
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key = bytes.fromhex('80 81 82 83 84 85 86 87 88 89 8a 8b 8c 8d 8e 8f 90 91 92 93 94 95 96 97 98 99 9a 9b 9c 9d 9e 9f')
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iv = b'@ABCDEFG'
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constant = bytes.fromhex('07 00 00 00')
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nonce = constant + iv
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print(chapoly_aead_enc(aad, key, nonce, plaintext) == bytes.fromhex('d3 1a 8d 34 64 8e 60 db 7b 86 af bc 53 ef 7e c2 a4 ad ed 51 29 6e 08 fe a9 e2 b5 a7 36 ee 62 d6 3d be a4 5e 8c a9 67 12 82 fa fb 69 da 92 72 8b 1a 71 de 0a 9e 06 0b 29 05 d6 a5 b6 7e cd 3b 36 92 dd bd 7f 2d 77 8b 8c 98 03 ae e3 28 09 1b 58 fa b3 24 e4 fa d6 75 94 55 85 80 8b 48 31 d7 bc 3f f4 de f0 8e 4b 7a 9d e5 76 d2 65 86 ce c6 4b 61 16 1a:e1:0b:59:4f:09:e2:6a:7e:90:2e:cb:d0:60:06:91'.replace(':','')))
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