63 lines
2 KiB
Python
63 lines
2 KiB
Python
from typing import Tuple
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from Crypto.Hash import SHA256
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from Crypto.Protocol.KDF import HKDF
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def rfc3526_group14() -> Tuple[int, int]:
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p_hex = (
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"FFFFFFFFFFFFFFFFC90FDAA22168C234C4C6628B80DC1CD1"
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"29024E088A67CC74020BBEA63B139B22514A08798E3404DD"
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"EF9519B3CD3A431B302B0A6DF25F14374FE1356D6D51C245"
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"E485B576625E7EC6F44C42E9A637ED6B0BFF5CB6F406B7ED"
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"EE386BFB5A899FA5AE9F24117C4B1FE649286651ECE45B3D"
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"C2007CB8A163BF0598DA48361C55D39A69163FA8FD24CF5F"
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"83655D23DCA3AD961C62F356208552BB9ED529077096966D"
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"670C354E4ABC9804F1746C08CA18217C32905E462E36CE3B"
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"E39E772C180E86039B2783A2EC07A28FB5C55DF06F4C52C9"
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"DE2BCBF6955817183995497CEA956AE515D2261898FA0510"
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"15728E5A8AACAA68FFFFFFFFFFFFFFFF"
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)
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return int(p_hex, 16), 2
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def int_to_fixed_length_bytes(value: int, length_bits: int) -> bytes:
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length_bytes = (length_bits + 7) // 8
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return value.to_bytes(length_bytes, byteorder="big")
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def dh_keypair(p: int, g: int, private_bits: int = 256) -> Tuple[int, int]:
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from Crypto.Util import number
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a = 0
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while a < 2:
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a = number.getRandomNBitInteger(private_bits)
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A = pow(g, a, p)
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return a, A
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def main() -> None:
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p, g = rfc3526_group14()
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a_priv, a_pub = dh_keypair(p, g)
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b_priv, b_pub = dh_keypair(p, g)
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a_shared = pow(b_pub, a_priv, p)
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b_shared = pow(a_pub, b_priv, p)
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same = (a_shared == b_shared)
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print("Lab6: Basic Diffie-Hellman (no symmetric cipher)")
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print(f"- Group: p({p.bit_length()} bits), g={g}")
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print(f"- A public: {hex(a_pub)[:18]}...")
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print(f"- B public: {hex(b_pub)[:18]}...")
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print(f"- Shared equal: {same}")
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# Optionally derive a fixed-length key material to show post-processing (not used to encrypt)
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shared_bytes = int_to_fixed_length_bytes(a_shared, p.bit_length())
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key_material = HKDF(shared_bytes, 32, salt=None, hashmod=SHA256, context=b"demo")
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print(f"- Derived key material (SHA256/HKDF) prefix: {key_material.hex()[:16]}...")
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if __name__ == "__main__":
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main()
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