Node / public / precursor-lxmfchat.git / files / reference / validate_link_proof.py

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#!/usr/bin/env python3

"""Replicate RNS initiator's Link.validate_proof to check our responder's proof.

validate_link_proof.py <our_pubkey_hex> <request_raw_hex> <link_id_hex> <proof_raw_hex>

"""

import sys

import RNS

ECPUBSIZE = 64

SIGLEN = 64

LINK_MTU_SIZE = 3

MTU_BYTEMASK = 0x1FFFFF

def get_hashable_part(raw):

hp = bytes([raw[0] & 0x0F])

header_type = (raw[0] & 0b01000000) >> 6

if header_type == 1: # HEADER_2

hp += raw[(128 // 8) + 2:]

else:

hp += raw[2:]

return hp

def link_id_from_request(raw):

hp = get_hashable_part(raw)

# data starts after flags(1)+hops(1)+dest(16)+context(1) = 19 for HEADER_1

data = raw[19:]

if len(data) > ECPUBSIZE:

diff = len(data) - ECPUBSIZE

hp = hp[:-diff]

return RNS.Identity.truncated_hash(hp)

def main():

our_pub = bytes.fromhex(sys.argv[1])

request_raw = bytes.fromhex(sys.argv[2])

given_link_id = bytes.fromhex(sys.argv[3])

proof_raw = bytes.fromhex(sys.argv[4])

# recompute link id from the request the RNS way

link_id = link_id_from_request(request_raw)

print("link_id match:", link_id == given_link_id, link_id.hex())

# proof packet is HEADER_1: data starts at offset 19

proof_data = proof_raw[19:]

print("proof_data len:", len(proof_data), "(expect 99 = 64 sig + 32 pub + 3 signalling)")

mode = proof_data[ECPUBSIZE + SIGLEN - 64 + 96 - 96] if False else (proof_data[96] >> 5)

signalling = proof_data[96:99]

peer_pub = proof_data[SIGLEN:SIGLEN + 32]

peer_sig_pub = our_pub[32:64]

signed = link_id + peer_pub + peer_sig_pub + signalling

signature = proof_data[:SIGLEN]

idn = RNS.Identity(create_keys=False)

idn.load_public_key(our_pub)

valid = idn.validate(signature, signed)

print("mode:", mode, "(expect 1 = AES256)")

print("signature valid:", bool(valid))

if __name__ == "__main__":

main()