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317 lines
10 KiB
C++
317 lines
10 KiB
C++
//------------------------------------------------------------------------------
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/*
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Copyright (c) 2011-2013, OpenCoin, Inc.
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*/
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//==============================================================================
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// ECIES uses elliptic curve keys to send an encrypted message.
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// A shared secret is generated from one public key and one private key.
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// The same key results regardless of which key is public and which private.
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// Anonymous messages can be sent by generating an ephemeral public/private
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// key pair, using that private key with the recipient's public key to
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// encrypt and publishing the ephemeral public key. Non-anonymous messages
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// can be sent by using your own private key with the recipient's public key.
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// A random IV is used to encrypt the message and an HMAC is used to ensure
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// message integrity. If you need timestamps or need to tell the recipient
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// which key to use (his, yours, or ephemeral) you must add that data.
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// (Obviously, key information can't go in the encrypted portion anyway.)
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// Our ciphertext is all encrypted except the IV. The encrypted data decodes as follows:
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// 1) IV (unencrypted)
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// 2) Encrypted: HMAC of original plaintext
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// 3) Encrypted: Original plaintext
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// 4) Encrypted: Rest of block/padding
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// ECIES operations throw on any error such as a corrupt message or incorrect
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// key. They *must* be called in try/catch blocks.
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// Algorithmic choices:
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#define ECIES_KEY_HASH SHA512 // Hash used to expand shared secret
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#define ECIES_KEY_LENGTH (512/8) // Size of expanded shared secret
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#define ECIES_MIN_SEC (128/8) // The minimum equivalent security
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#define ECIES_ENC_ALGO EVP_aes_256_cbc() // Encryption algorithm
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#define ECIES_ENC_KEY_TYPE uint256 // Type used to hold shared secret
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#define ECIES_ENC_KEY_SIZE (256/8) // Encryption key size
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#define ECIES_ENC_BLK_SIZE (128/8) // Encryption block size
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#define ECIES_ENC_IV_TYPE uint128 // Type used to hold IV
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#define ECIES_HMAC_ALGO EVP_sha256() // HMAC algorithm
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#define ECIES_HMAC_KEY_TYPE uint256 // Type used to hold HMAC key
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#define ECIES_HMAC_KEY_SIZE (256/8) // Size of HMAC key
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#define ECIES_HMAC_TYPE uint256 // Type used to hold HMAC value
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#define ECIES_HMAC_SIZE (256/8) // Size of HMAC value
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void CKey::getECIESSecret (CKey& otherKey, ECIES_ENC_KEY_TYPE& enc_key, ECIES_HMAC_KEY_TYPE& hmac_key)
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{
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// Retrieve a secret generated from an EC key pair. At least one private key must be known.
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if (!pkey || !otherKey.pkey)
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throw std::runtime_error ("missing key");
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EC_KEY* pubkey, *privkey;
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if (EC_KEY_get0_private_key (pkey))
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{
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privkey = pkey;
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pubkey = otherKey.pkey;
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}
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else if (EC_KEY_get0_private_key (otherKey.pkey))
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{
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privkey = otherKey.pkey;
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pubkey = pkey;
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}
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else throw std::runtime_error ("no private key");
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unsigned char rawbuf[512];
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int buflen = ECDH_compute_key (rawbuf, 512, EC_KEY_get0_public_key (pubkey), privkey, NULL);
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if (buflen < ECIES_MIN_SEC)
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throw std::runtime_error ("ecdh key failed");
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unsigned char hbuf[ECIES_KEY_LENGTH];
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ECIES_KEY_HASH (rawbuf, buflen, hbuf);
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memset (rawbuf, 0, ECIES_HMAC_KEY_SIZE);
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assert ((ECIES_ENC_KEY_SIZE + ECIES_HMAC_KEY_SIZE) >= ECIES_KEY_LENGTH);
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memcpy (enc_key.begin (), hbuf, ECIES_ENC_KEY_SIZE);
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memcpy (hmac_key.begin (), hbuf + ECIES_ENC_KEY_SIZE, ECIES_HMAC_KEY_SIZE);
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memset (hbuf, 0, ECIES_KEY_LENGTH);
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}
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static ECIES_HMAC_TYPE makeHMAC (const ECIES_HMAC_KEY_TYPE& secret, Blob const& data)
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{
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HMAC_CTX ctx;
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HMAC_CTX_init (&ctx);
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if (HMAC_Init_ex (&ctx, secret.begin (), ECIES_HMAC_KEY_SIZE, ECIES_HMAC_ALGO, NULL) != 1)
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{
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HMAC_CTX_cleanup (&ctx);
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throw std::runtime_error ("init hmac");
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}
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if (HMAC_Update (&ctx, & (data.front ()), data.size ()) != 1)
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{
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HMAC_CTX_cleanup (&ctx);
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throw std::runtime_error ("update hmac");
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}
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ECIES_HMAC_TYPE ret;
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unsigned int ml = ECIES_HMAC_SIZE;
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if (HMAC_Final (&ctx, ret.begin (), &ml) != 1)
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{
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HMAC_CTX_cleanup (&ctx);
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throw std::runtime_error ("finalize hmac");
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}
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assert (ml == ECIES_HMAC_SIZE);
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HMAC_CTX_cleanup (&ctx);
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return ret;
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}
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Blob CKey::encryptECIES (CKey& otherKey, Blob const& plaintext)
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{
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ECIES_ENC_IV_TYPE iv;
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RandomNumbers::getInstance ().fillBytes (iv.begin (), ECIES_ENC_BLK_SIZE);
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ECIES_ENC_KEY_TYPE secret;
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ECIES_HMAC_KEY_TYPE hmacKey;
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getECIESSecret (otherKey, secret, hmacKey);
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ECIES_HMAC_TYPE hmac = makeHMAC (hmacKey, plaintext);
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hmacKey.zero ();
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EVP_CIPHER_CTX ctx;
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EVP_CIPHER_CTX_init (&ctx);
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if (EVP_EncryptInit_ex (&ctx, ECIES_ENC_ALGO, NULL, secret.begin (), iv.begin ()) != 1)
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{
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EVP_CIPHER_CTX_cleanup (&ctx);
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secret.zero ();
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throw std::runtime_error ("init cipher ctx");
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}
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secret.zero ();
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Blob out (plaintext.size () + ECIES_HMAC_SIZE + ECIES_ENC_KEY_SIZE + ECIES_ENC_BLK_SIZE, 0);
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int len = 0, bytesWritten;
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// output IV
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memcpy (& (out.front ()), iv.begin (), ECIES_ENC_BLK_SIZE);
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len = ECIES_ENC_BLK_SIZE;
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// Encrypt/output HMAC
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bytesWritten = out.capacity () - len;
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assert (bytesWritten > 0);
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if (EVP_EncryptUpdate (&ctx, & (out.front ()) + len, &bytesWritten, hmac.begin (), ECIES_HMAC_SIZE) < 0)
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{
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EVP_CIPHER_CTX_cleanup (&ctx);
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throw std::runtime_error ("");
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}
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len += bytesWritten;
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// encrypt/output plaintext
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bytesWritten = out.capacity () - len;
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assert (bytesWritten > 0);
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if (EVP_EncryptUpdate (&ctx, & (out.front ()) + len, &bytesWritten, & (plaintext.front ()), plaintext.size ()) < 0)
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{
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EVP_CIPHER_CTX_cleanup (&ctx);
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throw std::runtime_error ("");
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}
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len += bytesWritten;
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// finalize
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bytesWritten = out.capacity () - len;
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if (EVP_EncryptFinal_ex (&ctx, & (out.front ()) + len, &bytesWritten) < 0)
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{
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EVP_CIPHER_CTX_cleanup (&ctx);
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throw std::runtime_error ("encryption error");
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}
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len += bytesWritten;
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// Output contains: IV, encrypted HMAC, encrypted data, encrypted padding
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assert (len <= (plaintext.size () + ECIES_HMAC_SIZE + (2 * ECIES_ENC_BLK_SIZE)));
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assert (len >= (plaintext.size () + ECIES_HMAC_SIZE + ECIES_ENC_BLK_SIZE)); // IV, HMAC, data
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out.resize (len);
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EVP_CIPHER_CTX_cleanup (&ctx);
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return out;
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}
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Blob CKey::decryptECIES (CKey& otherKey, Blob const& ciphertext)
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{
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// minimum ciphertext = IV + HMAC + 1 block
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if (ciphertext.size () < ((2 * ECIES_ENC_BLK_SIZE) + ECIES_HMAC_SIZE) )
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throw std::runtime_error ("ciphertext too short");
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// extract IV
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ECIES_ENC_IV_TYPE iv;
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memcpy (iv.begin (), & (ciphertext.front ()), ECIES_ENC_BLK_SIZE);
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// begin decrypting
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EVP_CIPHER_CTX ctx;
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EVP_CIPHER_CTX_init (&ctx);
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ECIES_ENC_KEY_TYPE secret;
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ECIES_HMAC_KEY_TYPE hmacKey;
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getECIESSecret (otherKey, secret, hmacKey);
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if (EVP_DecryptInit_ex (&ctx, ECIES_ENC_ALGO, NULL, secret.begin (), iv.begin ()) != 1)
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{
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secret.zero ();
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hmacKey.zero ();
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EVP_CIPHER_CTX_cleanup (&ctx);
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throw std::runtime_error ("unable to init cipher");
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}
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// decrypt mac
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ECIES_HMAC_TYPE hmac;
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int outlen = ECIES_HMAC_SIZE;
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if ( (EVP_DecryptUpdate (&ctx, hmac.begin (), &outlen,
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& (ciphertext.front ()) + ECIES_ENC_BLK_SIZE, ECIES_HMAC_SIZE + 1) != 1) || (outlen != ECIES_HMAC_SIZE) )
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{
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secret.zero ();
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hmacKey.zero ();
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EVP_CIPHER_CTX_cleanup (&ctx);
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throw std::runtime_error ("unable to extract hmac");
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}
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// decrypt plaintext (after IV and encrypted mac)
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Blob plaintext (ciphertext.size () - ECIES_HMAC_SIZE - ECIES_ENC_BLK_SIZE);
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outlen = plaintext.size ();
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if (EVP_DecryptUpdate (&ctx, & (plaintext.front ()), &outlen,
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& (ciphertext.front ()) + ECIES_ENC_BLK_SIZE + ECIES_HMAC_SIZE + 1,
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ciphertext.size () - ECIES_ENC_BLK_SIZE - ECIES_HMAC_SIZE - 1) != 1)
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{
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secret.zero ();
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hmacKey.zero ();
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EVP_CIPHER_CTX_cleanup (&ctx);
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throw std::runtime_error ("unable to extract plaintext");
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}
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// decrypt padding
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int flen = 0;
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if (EVP_DecryptFinal (&ctx, & (plaintext.front ()) + outlen, &flen) != 1)
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{
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secret.zero ();
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hmacKey.zero ();
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EVP_CIPHER_CTX_cleanup (&ctx);
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throw std::runtime_error ("plaintext had bad padding");
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}
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plaintext.resize (flen + outlen);
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// verify integrity
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if (hmac != makeHMAC (hmacKey, plaintext))
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{
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secret.zero ();
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hmacKey.zero ();
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EVP_CIPHER_CTX_cleanup (&ctx);
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throw std::runtime_error ("plaintext had bad hmac");
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}
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secret.zero ();
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hmacKey.zero ();
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EVP_CIPHER_CTX_cleanup (&ctx);
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return plaintext;
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}
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bool checkECIES (void)
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{
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CKey senderPriv, recipientPriv, senderPub, recipientPub;
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for (int i = 0; i < 30000; ++i)
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{
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if ((i % 100) == 0)
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{
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// generate new keys every 100 times
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// std::cerr << "new keys" << std::endl;
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senderPriv.MakeNewKey ();
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recipientPriv.MakeNewKey ();
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if (!senderPub.SetPubKey (senderPriv.GetPubKey ()))
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throw std::runtime_error ("key error");
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if (!recipientPub.SetPubKey (recipientPriv.GetPubKey ()))
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throw std::runtime_error ("key error");
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}
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// generate message
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Blob message (4096);
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int msglen = i % 3000;
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RandomNumbers::getInstance ().fillBytes (&message.front (), msglen);
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message.resize (msglen);
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// encrypt message with sender's private key and recipient's public key
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Blob ciphertext = senderPriv.encryptECIES (recipientPub, message);
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// decrypt message with recipient's private key and sender's public key
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Blob decrypt = recipientPriv.decryptECIES (senderPub, ciphertext);
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if (decrypt != message)
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{
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assert (false);
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return false;
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}
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// std::cerr << "Msg(" << msglen << ") ok " << ciphertext.size() << std::endl;
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}
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return true;
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}
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// vim:ts=4
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