sign.cxx

#include "cagliostr.hxx"

#include <openssl/evp.h>

#include <secp256k1.h>
#include <secp256k1_schnorrsig.h>

static inline std::vector<uint8_t> hex2bytes(const std::string &hex) {
  std::vector<uint8_t> bytes;
  for (decltype(hex.length()) i = 0; i < hex.length(); i += 2) {
    std::string s = hex.substr(i, 2);
    auto byte = (uint8_t)strtol(s.c_str(), nullptr, 16);
    bytes.push_back(byte);
  }
  return bytes;
}

static inline std::string digest2hex(const uint8_t data[32]) {
  std::stringstream ss;
  ss << std::hex;
  for (size_t i = 0; i < 32; ++i) {
    ss << std::setw(2) << std::setfill('0') << (int)data[i];
  }
  return ss.str();
}

static bool signature_verify(const std::vector<uint8_t> &bytes_sig,
                             const std::vector<uint8_t> &bytes_pub,
                             const uint8_t digest[32]) {
#define secp256k1_context_flags                                                \
  (SECP256K1_CONTEXT_SIGN | SECP256K1_CONTEXT_VERIFY)
  secp256k1_context *ctx = secp256k1_context_create(secp256k1_context_flags);
  secp256k1_xonly_pubkey pub;
  if (!secp256k1_xonly_pubkey_parse(ctx, &pub, bytes_pub.data())) {
    secp256k1_context_destroy(ctx);
    return false;
  }

  auto result = secp256k1_schnorrsig_verify(ctx, bytes_sig.data(), digest,
#ifdef SECP256K1_SCHNORRSIG_EXTRAPARAMS_INIT
                                            32,
#endif
                                            &pub);
  secp256k1_context_destroy(ctx);
  return result;
}

bool check_event(const event_t &ev) {
  nlohmann::json check = {0,       ev.pubkey, ev.created_at,
                          ev.kind, ev.tags,   ev.content};
  auto dump = check.dump();
  check.clear();

  uint8_t digest[32] = {0};
  EVP_Digest(dump.data(), dump.size(), digest, nullptr, EVP_sha256(), nullptr);

  auto id = digest2hex(digest);
  if (id != ev.id) {
    return false;
  }

  auto bytes_sig = hex2bytes(ev.sig);
  auto bytes_pub = hex2bytes(ev.pubkey);
  if (!signature_verify(bytes_sig, bytes_pub, digest)) {
    return false;
  }
  return true;
}