Blob decryptECIES (const openssl::ec_key& secretKey, const openssl::ec_key& publicKey, Blob const& ciphertext)
{
// minimum ciphertext = IV + HMAC + 1 block
if (ciphertext.size () < ((2 * ECIES_ENC_BLK_SIZE) + ECIES_HMAC_SIZE) )
throw std::runtime_error ("ciphertext too short");
// extract IV
ECIES_ENC_IV_TYPE iv;
memcpy (iv.begin (), & (ciphertext.front ()), ECIES_ENC_BLK_SIZE);
// begin decrypting
EVP_CIPHER_CTX ctx;
EVP_CIPHER_CTX_init (&ctx);
ECIES_ENC_KEY_TYPE secret;
ECIES_HMAC_KEY_TYPE hmacKey;
getECIESSecret (secretKey, publicKey, secret, hmacKey);
if (EVP_DecryptInit_ex (&ctx, ECIES_ENC_ALGO, nullptr, secret.begin (), iv.begin ()) != 1)
{
secret.zero ();
hmacKey.zero ();
EVP_CIPHER_CTX_cleanup (&ctx);
throw std::runtime_error ("unable to init cipher");
}
// decrypt mac
ECIES_HMAC_TYPE hmac;
int outlen = ECIES_HMAC_SIZE;
if ( (EVP_DecryptUpdate (&ctx, hmac.begin (), &outlen,
& (ciphertext.front ()) + ECIES_ENC_BLK_SIZE, ECIES_HMAC_SIZE + 1) != 1) || (outlen != ECIES_HMAC_SIZE) )
{
secret.zero ();
hmacKey.zero ();
EVP_CIPHER_CTX_cleanup (&ctx);
throw std::runtime_error ("unable to extract hmac");
}
// decrypt plaintext (after IV and encrypted mac)
Blob plaintext (ciphertext.size () - ECIES_HMAC_SIZE - ECIES_ENC_BLK_SIZE);
outlen = plaintext.size ();
if (EVP_DecryptUpdate (&ctx, & (plaintext.front ()), &outlen,
& (ciphertext.front ()) + ECIES_ENC_BLK_SIZE + ECIES_HMAC_SIZE + 1,
ciphertext.size () - ECIES_ENC_BLK_SIZE - ECIES_HMAC_SIZE - 1) != 1)
{
secret.zero ();
hmacKey.zero ();
EVP_CIPHER_CTX_cleanup (&ctx);
throw std::runtime_error ("unable to extract plaintext");
}
// decrypt padding
int flen = 0;
if (EVP_DecryptFinal (&ctx, & (plaintext.front ()) + outlen, &flen) != 1)
{
secret.zero ();
hmacKey.zero ();
EVP_CIPHER_CTX_cleanup (&ctx);
throw std::runtime_error ("plaintext had bad padding");
}
plaintext.resize (flen + outlen);
// verify integrity
if (hmac != makeHMAC (hmacKey, plaintext))
{
secret.zero ();
hmacKey.zero ();
EVP_CIPHER_CTX_cleanup (&ctx);
throw std::runtime_error ("plaintext had bad hmac");
}
secret.zero ();
hmacKey.zero ();
EVP_CIPHER_CTX_cleanup (&ctx);
return plaintext;
}
Blob encryptECIES (const openssl::ec_key& secretKey, const openssl::ec_key& publicKey, Blob const& plaintext)
{
ECIES_ENC_IV_TYPE iv;
random_fill (iv.begin (), ECIES_ENC_BLK_SIZE);
ECIES_ENC_KEY_TYPE secret;
ECIES_HMAC_KEY_TYPE hmacKey;
getECIESSecret (secretKey, publicKey, secret, hmacKey);
ECIES_HMAC_TYPE hmac = makeHMAC (hmacKey, plaintext);
hmacKey.zero ();
EVP_CIPHER_CTX ctx;
EVP_CIPHER_CTX_init (&ctx);
if (EVP_EncryptInit_ex (&ctx, ECIES_ENC_ALGO, nullptr, secret.begin (), iv.begin ()) != 1)
{
EVP_CIPHER_CTX_cleanup (&ctx);
secret.zero ();
throw std::runtime_error ("init cipher ctx");
}
secret.zero ();
Blob out (plaintext.size () + ECIES_HMAC_SIZE + ECIES_ENC_KEY_SIZE + ECIES_ENC_BLK_SIZE, 0);
int len = 0, bytesWritten;
// output IV
memcpy (& (out.front ()), iv.begin (), ECIES_ENC_BLK_SIZE);
len = ECIES_ENC_BLK_SIZE;
// Encrypt/output HMAC
bytesWritten = out.capacity () - len;
assert (bytesWritten > 0);
if (EVP_EncryptUpdate (&ctx, & (out.front ()) + len, &bytesWritten, hmac.begin (), ECIES_HMAC_SIZE) < 0)
{
EVP_CIPHER_CTX_cleanup (&ctx);
throw std::runtime_error ("");
}
len += bytesWritten;
// encrypt/output plaintext
bytesWritten = out.capacity () - len;
assert (bytesWritten > 0);
if (EVP_EncryptUpdate (&ctx, & (out.front ()) + len, &bytesWritten, & (plaintext.front ()), plaintext.size ()) < 0)
{
EVP_CIPHER_CTX_cleanup (&ctx);
throw std::runtime_error ("");
}
len += bytesWritten;
// finalize
bytesWritten = out.capacity () - len;
if (EVP_EncryptFinal_ex (&ctx, & (out.front ()) + len, &bytesWritten) < 0)
{
EVP_CIPHER_CTX_cleanup (&ctx);
throw std::runtime_error ("encryption error");
}
len += bytesWritten;
// Output contains: IV, encrypted HMAC, encrypted data, encrypted padding
assert (len <= (plaintext.size () + ECIES_HMAC_SIZE + (2 * ECIES_ENC_BLK_SIZE)));
assert (len >= (plaintext.size () + ECIES_HMAC_SIZE + ECIES_ENC_BLK_SIZE)); // IV, HMAC, data
out.resize (len);
EVP_CIPHER_CTX_cleanup (&ctx);
return out;
}
