Module: Runar::RabinSig

Defined in:
lib/runar/rabin_sig.rb

Class Method Summary collapse

Class Method Details

.rabin_verify(msg_hex, sig_hex, pad_hex, pubkey_hex) ⇒ Boolean

Verify a Rabin signature.

All parameters are hex-encoded strings. sig, padding, and pubkey are interpreted as unsigned little-endian integers.

— No domain separation —

The message is hashed directly (SHA-256(msg)) without any domain prefix or context tag. This is inherent to the Rabin signature scheme as used in Bitcoin Script contracts: the locking script encodes the raw hash check, so introducing a domain prefix would change the expected hash value and break existing deployed contracts.

The practical implication is that two different applications using the same Rabin key could have cross-signature validity: a signature produced for application A’s message is also a valid Rabin signature for that same byte sequence in application B. Callers are responsible for ensuring messages are structurally distinct across use cases (e.g. by including a contract-specific nonce or type tag in the message before signing).

Parameters:

  • msg_hex (String) —

    hex-encoded message bytes

  • sig_hex (String) —

    hex-encoded signature (unsigned LE integer)

  • pad_hex (String) —

    hex-encoded padding (unsigned LE integer)

  • pubkey_hex (String) —

    hex-encoded public key / modulus (unsigned LE integer)

Returns:

  • (Boolean) —

    true if the signature is valid



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# File 'lib/runar/rabin_sig.rb', line 44

def self.rabin_verify(msg_hex, sig_hex, pad_hex, pubkey_hex)
  n = bytes_to_unsigned_le([pubkey_hex].pack('H*'))
  return false if n <= 0

  sig_int = bytes_to_unsigned_le([sig_hex].pack('H*'))
  pad_int = bytes_to_unsigned_le([pad_hex].pack('H*'))

  msg_bytes = [msg_hex].pack('H*')
  hash_bytes = Digest::SHA256.digest(msg_bytes)
  hash_int = bytes_to_unsigned_le(hash_bytes)

  lhs = (sig_int * sig_int + pad_int) % n
  rhs = hash_int % n
  lhs == rhs
end