oc-mint/test/test_crypto.cpp

#include <catch2/catch_test_macros.hpp>

#include "cryptlib.h"
#include "integer.h"
#include "nbtheory.h"
#include "osrng.h"
#include "rsa.h"
#include "sha.h"

#include <iostream>
#include <stdexcept>


CryptoPP::Integer blind_signature(unsigned char *msg,
				size_t msg_len,

				const CryptoPP::RSA::PublicKey& pub_key,
				const CryptoPP::RSA::PrivateKey& priv_key) {
  using namespace CryptoPP;
  using std::cout;
  using std::endl;
  AutoSeededRandomPool prng;

    // Convenience
  const Integer &n = pub_key.GetModulus();
  const Integer &e = pub_key.GetPublicExponent();
  const Integer &d = priv_key.GetPrivateExponent();

// For sizing the hashed message buffer. This should be SHA256 size.
  const size_t sig_size = UnsignedMin(SHA256::BLOCKSIZE, n.ByteCount());
// Scratch
  SecByteBlock buff_1, buff_2, buff_3;

  SecByteBlock orig(msg, msg_len);
  Integer m(orig.data(), orig.size());
  cout << "Message: " << std::hex << m << endl;

  // Hash message per Rabin (1979)
  buff_1.resize(sig_size);
  SHA256 hash_1;
  hash_1.CalculateTruncatedDigest(buff_1, buff_1.size(), orig, orig.size());

  // H(m) as Integer
  Integer hm(buff_1.data(), buff_1.size());
  cout << "H(m): " << std::hex << hm << endl;

  // Alice blinding
  Integer r;
  do {
    r.Randomize(prng, Integer::One(), n - Integer::One());
  } while (!RelativelyPrime(r, n));

  // Blinding factor
  Integer b = a_exp_b_mod_c(r, e, n);
  cout << "Random: " << std::hex << b << endl;

  // Alice blinded message
  Integer mm = a_times_b_mod_c(hm, b, n);
  cout << "Blind msg: " << std::hex << mm << endl;

    // Bob sign
  Integer ss = priv_key.CalculateInverse(prng, mm);
  cout << "Blind sign: " << ss << endl;

  return ss;
}

TEST_CASE("cryptopp", "[crypto]") {
  using namespace CryptoPP;
  using std::cout;
  using std::endl;
  using std::runtime_error;

  // Bob artificially small key pair
  AutoSeededRandomPool prng;
  RSA::PrivateKey priv_key;

  priv_key.GenerateRandomWithKeySize(prng, 64U);
  RSA::PublicKey pub_key(priv_key);

  // Convenience
  const Integer &n = pub_key.GetModulus();
  const Integer &e = pub_key.GetPublicExponent();
  const Integer &d = priv_key.GetPrivateExponent();

  // Print params
  cout << "Pub mod: " << std::hex << pub_key.GetModulus() << endl;
  cout << "Pub exp: " << std::hex << e << endl;
  cout << "Priv mod: " << std::hex << priv_key.GetModulus() << endl;
  cout << "Priv exp: " << std::hex << d << endl;

  // For sizing the hashed message buffer. This should be SHA256 size.
  const size_t sig_size = UnsignedMin(SHA256::BLOCKSIZE, n.ByteCount());

  // Scratch
  SecByteBlock buff_1, buff_2, buff_3;

  // Alice original message to be signed by Bob
  SecByteBlock orig((const byte *)"secret", 6U);
  Integer m(orig.data(), orig.size());
  cout << "Message: " << std::hex << m << endl;

  // Hash message per Rabin (1979)
  buff_1.resize(sig_size);
  SHA256 hash_1;
  hash_1.CalculateTruncatedDigest(buff_1, buff_1.size(), orig, orig.size());

  // H(m) as Integer
  Integer hm(buff_1.data(), buff_1.size());
  cout << "H(m): " << std::hex << hm << endl;

  // Alice blinding
  Integer r;
  do {
    r.Randomize(prng, Integer::One(), n - Integer::One());
  } while (!RelativelyPrime(r, n));

  // Blinding factor
  Integer b = a_exp_b_mod_c(r, e, n);
  cout << "Random: " << std::hex << b << endl;

  // Alice blinded message
  Integer mm = a_times_b_mod_c(hm, b, n);
  cout << "Blind msg: " << std::hex << mm << endl;

  // Bob sign
  Integer ss = priv_key.CalculateInverse(prng, mm);
  cout << "Blind sign: " << ss << endl;

  // Alice checks s(s'(x)) = x. This is from Chaum's paper
  Integer c = pub_key.ApplyFunction(ss);
  cout << "Check sign: " << c << endl;
  if (c != mm) {
    throw runtime_error("Alice cross-check failed");
  }
  // Alice remove blinding
  Integer s = a_times_b_mod_c(ss, r.InverseMod(n), n);
  cout << "Unblind sign: " << s << endl;

  // Eve verifies
  Integer v = pub_key.ApplyFunction(s);
  cout << "Verify: " << std::hex << v << endl;

  // Convert to a string
  size_t req = v.MinEncodedSize();
  buff_2.resize(req);
  v.Encode(&buff_2[0], buff_2.size());

  // Hash message per Rabin (1979)
  buff_3.resize(sig_size);
  SHA256 hash_2;
  hash_2.CalculateTruncatedDigest(buff_3, buff_3.size(), orig, orig.size());

  // Constant time compare
  bool equal = buff_2.size() == buff_3.size() &&
               VerifyBufsEqual(buff_2.data(), buff_3.data(), buff_3.size());

  if (!equal) {
    throw runtime_error("Eve verified failed");
  }
  cout << "Verified signature" << endl;
}