void Secp256k1PP::encryptECIES(Public const& _k, bytesConstRef _sharedMacData, bytes& io_cipher)
{
// interop w/go ecies implementation
auto r = KeyPair::create();
Secret z;
ecdh::agree(r.sec(), _k, z);
auto key = eciesKDF(z, bytes(), 32);
bytesConstRef eKey = bytesConstRef(&key).cropped(0, 16);
bytesRef mKeyMaterial = bytesRef(&key).cropped(16, 16);
CryptoPP::SHA256 ctx;
ctx.Update(mKeyMaterial.data(), mKeyMaterial.size());
bytes mKey(32);
ctx.Final(mKey.data());
bytes cipherText = encryptSymNoAuth(SecureFixedHash<16>(eKey), h128(), bytesConstRef(&io_cipher));
if (cipherText.empty())
return;
bytes msg(1 + Public::size + h128::size + cipherText.size() + 32);
msg[0] = 0x04;
r.pub().ref().copyTo(bytesRef(&msg).cropped(1, Public::size));
bytesRef msgCipherRef = bytesRef(&msg).cropped(1 + Public::size + h128::size, cipherText.size());
bytesConstRef(&cipherText).copyTo(msgCipherRef);
// tag message
CryptoPP::HMAC<SHA256> hmacctx(mKey.data(), mKey.size());
bytesConstRef cipherWithIV = bytesRef(&msg).cropped(1 + Public::size, h128::size + cipherText.size());
hmacctx.Update(cipherWithIV.data(), cipherWithIV.size());
hmacctx.Update(_sharedMacData.data(), _sharedMacData.size());
hmacctx.Final(msg.data() + 1 + Public::size + cipherWithIV.size());
io_cipher.resize(msg.size());
io_cipher.swap(msg);
}
bool Secp256k1PP::decryptECIES(Secret const& _k, bytesConstRef _sharedMacData, bytes& io_text)
{
// interop w/go ecies implementation
// io_cipher[0] must be 2, 3, or 4, else invalidpublickey
if (io_text.empty() || io_text[0] < 2 || io_text[0] > 4)
// invalid message: publickey
return false;
if (io_text.size() < (1 + Public::size + h128::size + 1 + h256::size))
// invalid message: length
return false;
Secret z;
if (!ecdh::agree(_k, *(Public*)(io_text.data() + 1), z))
return false; // Invalid pubkey or seckey.
auto key = ecies::kdf(z, bytes(), 64);
bytesConstRef eKey = bytesConstRef(&key).cropped(0, 16);
bytesRef mKeyMaterial = bytesRef(&key).cropped(16, 16);
bytes mKey(32);
CryptoPP::SHA256 ctx;
ctx.Update(mKeyMaterial.data(), mKeyMaterial.size());
ctx.Final(mKey.data());
bytes plain;
size_t cipherLen = io_text.size() - 1 - Public::size - h128::size - h256::size;
bytesConstRef cipherWithIV(io_text.data() + 1 + Public::size, h128::size + cipherLen);
bytesConstRef cipherIV = cipherWithIV.cropped(0, h128::size);
bytesConstRef cipherNoIV = cipherWithIV.cropped(h128::size, cipherLen);
bytesConstRef msgMac(cipherNoIV.data() + cipherLen, h256::size);
h128 iv(cipherIV.toBytes());
// verify tag
CryptoPP::HMAC<CryptoPP::SHA256> hmacctx(mKey.data(), mKey.size());
hmacctx.Update(cipherWithIV.data(), cipherWithIV.size());
hmacctx.Update(_sharedMacData.data(), _sharedMacData.size());
h256 mac;
hmacctx.Final(mac.data());
for (unsigned i = 0; i < h256::size; i++)
if (mac[i] != msgMac[i])
return false;
plain = decryptSymNoAuth(SecureFixedHash<16>(eKey), iv, cipherNoIV).makeInsecure();
io_text.resize(plain.size());
io_text.swap(plain);
return true;
}
