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所以我试图在一个 Objective-C 项目中使用 Crypto++ 的加密。问题在于如何处理 IV？我尝试将其预先附加到密文中。但是后来我在恢复它以进行解密时遇到了问题。

这是代码：

- (NSString *)encryptUsingSerpentWithPlaintext:(NSString *)plaintext andKey:(NSData *)keyData
{
    std::string ptext = [plaintext UTF8String];
    std::string ciphertext;

    byte key[ CryptoPP::Serpent::MAX_KEYLENGTH ], iv[ CryptoPP::Serpent::BLOCKSIZE ];

    CryptoPP::AutoSeededX917RNG<CryptoPP::Serpent> rng;
    rng.GenerateBlock(iv, CryptoPP::Serpent::BLOCKSIZE);

    std::string ivs(reinterpret_cast<char const *>(iv));
    lcl_log(lcl_cCrypto, lcl_vDebug, @"Random IV:%s",ivs.c_str());


    ::memcpy(key, keyData.bytes, keyData.length);


    CryptoPP::Serpent::Encryption serpentEncryptor (key, CryptoPP::Serpent::MAX_KEYLENGTH);
    CryptoPP::CBC_Mode_ExternalCipher::Encryption cbcSerpentEncryptor (serpentEncryptor, iv);

    CryptoPP::StreamTransformationFilter stfSerpentEncryptor(cbcSerpentEncryptor, new CryptoPP::StringSink (ciphertext));
    stfSerpentEncryptor.Put( reinterpret_cast<const unsigned char*>( ptext.c_str() ), ptext.length() + 1);
    stfSerpentEncryptor.MessageEnd();

    lcl_log(lcl_cCrypto, lcl_vDebug, @"Non-Encoded ciphertext [size:%lu]:%s",sizeof(ciphertext),ciphertext.c_str());

    std::string finalCT;

    ciphertext = ivs + ciphertext; // add the IV before the ciphertext

    lcl_log(lcl_cCrypto, lcl_vDebug, @"Non-Encoded iv+ciphertext [size:%lu]:%s",sizeof(ciphertext),ciphertext.c_str());

    CryptoPP::StringSource base64Encoder (ciphertext, true, new CryptoPP::Base64Encoder(new CryptoPP::StringSink(finalCT)));

    // apply HMAC
    // TO DO

    NSString *cryptogram = [NSString stringWithUTF8String:finalCT.c_str()];

    return cryptogram;
}

- (NSString *)decryptUsingSerpentWithCiphertext:(NSString *)ciphertext andKey:(NSData *)keyData
{
    std::string ctext;
    std::string plaintext;

    byte key[ CryptoPP::Serpent::MAX_KEYLENGTH ], iv[ CryptoPP::Serpent::BLOCKSIZE ];

    ::memcpy(key, keyData.bytes, keyData.length);

    // decode from base64
    std::string encoded = [ciphertext UTF8String];
    CryptoPP::StringSource base64Decoder (encoded, true, new CryptoPP::Base64Decoder(new CryptoPP::StringSink(ctext)));

    lcl_log(lcl_cCrypto, lcl_vDebug, @"Non-Encoded iv+ciphertext [size:%lu]:%s",sizeof(ctext),ctext.c_str());

    // get the IV from the beggining of the cryptogram
    std::string ivs = ctext.substr(0,CryptoPP::Serpent::BLOCKSIZE+5);

    lcl_log(lcl_cCrypto, lcl_vDebug, @"Recovered IV:%s",ivs.c_str());

    ::memcpy(iv, &ivs, ivs.size());

    // remove the IV from the cryptogram

    ctext.erase(0,CryptoPP::Serpent::BLOCKSIZE+5);

    lcl_log(lcl_cCrypto, lcl_vDebug, @"Non-Encoded ciphertext [size:%lu]:%s",sizeof(ctext),ctext.c_str());


    CryptoPP::Serpent::Decryption serpentDecryptor (key, CryptoPP::Serpent::MAX_KEYLENGTH);
    CryptoPP::CBC_Mode_ExternalCipher::Decryption cbcSerpentDecryptor (serpentDecryptor, iv);

    CryptoPP::StreamTransformationFilter stfSerpentDecryptor(cbcSerpentDecryptor, new CryptoPP::StringSink (plaintext));
    stfSerpentDecryptor.Put( reinterpret_cast<const unsigned char*>( ctext.c_str() ), ctext.length());
    stfSerpentDecryptor.MessageEnd();

    NSString *plainText = [NSString stringWithUTF8String:plaintext.c_str()];

    return plainText;
}

请注意，我需要将 5 添加到预期的 iv 大小才能获得完整的 IV。然后我收到一个关于“发现无效的 PCKS#7 填充。无效的密文”的错误

如何最好地管理静脉输液？（我还想在 iv+ciphertext 中添加一个 HMAC（Encrypt-then-MAC）...

如果我这样做：

// get the IV from the beggining of the cryptogram
std::string ivs = ctext.substr(0,CryptoPP::Serpent::BLOCKSIZE);

lcl_log(lcl_cCrypto, lcl_vDebug, @"Recovered IV:%s",ivs.c_str());

::memcpy(iv, &ivs, ivs.size());

// remove the IV from the cryptogram

ctext.erase(0,CryptoPP::Serpent::BLOCKSIZE);

日志将显示仍然在密文中的一些 IV 字节，并生成“无效密文，大小不是块大小的倍数”异常。

日志：

2013-12-01 17:59:37.747 App[413:70b] D Crypto:PSCryptoCore.mm:51:-[PSCryptoCore testSerpentEncryptonMechanism] Initial plaintext:Serpentine and black...
2013-12-01 17:59:37.748 App[413:70b] D Crypto:PSCryptoCore.mm:74:-[PSCryptoCore encryptUsingSerpentWithPlaintext:andKey:] Random IV:ç©ìùËß,¬<ÎΩ9ZÑ0 Û
2013-12-01 17:59:37.749 App[413:70b] D Crypto:PSCryptoCore.mm:87:-[PSCryptoCore encryptUsingSerpentWithPlaintext:andKey:] Non-Encoded ciphertext [size:4]:PÉò»ÓÔҥ 1æIõ¶”Áˆ™8äºBmº†c
õ
2013-12-01 17:59:37.749 App[413:70b] D Crypto:PSCryptoCore.mm:93:-[PSCryptoCore encryptUsingSerpentWithPlaintext:andKey:] Non-Encoded iv+ciphertext [size:4]:ç©ìùËß,¬<ÎΩ9ZÑ0 ÛPÉò»ÓÔҥ 1æIõ¶”Áˆ™8äºBmº†c
õ
2013-12-01 17:59:37.750 App[413:70b] D Crypto:PSCryptoCore.mm:54:-[PSCryptoCore testSerpentEncryptonMechanism] ciphertext:C42pk53opyzCPOu9FDlahDAg8wgBUIOYyO7M0/G0IDG+SZum0+f2qjiKvA4RQm28HaBjCps=
2013-12-01 17:59:37.750 App[413:70b] D Crypto:PSCryptoCore.mm:118:-[PSCryptoCore decryptUsingSerpentWithCiphertext:andKey:] Non-Encoded iv+ciphertext [size:4]:ç©ìùËß,¬<ÎΩ9ZÑ0 ÛPÉò»ÓÔҥ 1æIõ¶”Áˆ™8äºBmº†c
õ
2013-12-01 17:59:37.752 App[413:70b] D Crypto:PSCryptoCore.mm:123:-[PSCryptoCore decryptUsingSerpentWithCiphertext:andKey:] Recovered IV:ç©ìùËß,¬<ÎΩ9ZÑ
2013-12-01 17:59:37.753 App[413:70b] D Crypto:PSCryptoCore.mm:131:-[PSCryptoCore decryptUsingSerpentWithCiphertext:andKey:] Non-Encoded ciphertext [size:4]:0 ÛPÉò»ÓÔҥ 1æIõ¶”Áˆ™8äºBmº†c
õ
libc++abi.dylib: terminating with uncaught exception of type CryptoPP::InvalidCiphertext: StreamTransformationFilter: ciphertext length is not a multiple of block size

请注意，在我尝试撤销它之后，IV 的一部分仍然在密文前面。这是为什么呢？

4

2 回答 2

4

预先设置 IV 是完全正确的。为什么要在块大小上加 5？从 Base-64 解码为数据。将第一个 BLOCKSIZE 字节作为 IV 拉出。解密剩余部分。

于 2013-11-29T21:57:21.837 回答
0

我设法修复它。这是代码

- (NSString *)encryptUsingSerpentWithPlaintext:(NSString *)plaintext andKey:(NSData *)keyData
{
    std::string ptext = [plaintext UTF8String];
    std::string ciphertext;

    byte key[ CryptoPP::Serpent::MAX_KEYLENGTH ], iv[ CryptoPP::Serpent::BLOCKSIZE ];

    CryptoPP::AutoSeededX917RNG<CryptoPP::Serpent> rng;
    rng.GenerateBlock(iv, CryptoPP::Serpent::BLOCKSIZE);

    std::string ivs(reinterpret_cast<char const *>(iv));
    lcl_log(lcl_cCrypto, lcl_vDebug, @"Random IV:%s",ivs.c_str());


    ::memcpy(key, keyData.bytes, keyData.length);


    CryptoPP::Serpent::Encryption serpentEncryptor (key, CryptoPP::Serpent::MAX_KEYLENGTH);
    CryptoPP::CBC_Mode_ExternalCipher::Encryption cbcSerpentEncryptor (serpentEncryptor, iv);

    CryptoPP::StreamTransformationFilter stfSerpentEncryptor(cbcSerpentEncryptor, new CryptoPP::StringSink (ciphertext),CryptoPP::StreamTransformationFilter::BlockPaddingScheme::ONE_AND_ZEROS_PADDING);
    stfSerpentEncryptor.Put( reinterpret_cast<const unsigned char*>( ptext.c_str() ), ptext.length() + 1);
    stfSerpentEncryptor.MessageEnd();

    lcl_log(lcl_cCrypto, lcl_vDebug, @"Non-Encoded ciphertext [size:%lu]:%s",sizeof(ciphertext),ciphertext.c_str());

    std::string finalCT;

    CryptoPP::StringSource base64Encoder (ciphertext, true, new CryptoPP::Base64Encoder(new CryptoPP::StringSink(finalCT)));

    std::string ivB64;

    CryptoPP::StringSource base64IVEncoder (ivs , true, new CryptoPP::Base64Encoder(new CryptoPP::StringSink(ivB64)));

    lcl_log(lcl_cCrypto, lcl_vDebug, @"IV base64[size:%lu]:%s",ivB64.length(),ivB64.c_str());

    finalCT = ivB64 + finalCT;

    lcl_log(lcl_cCrypto, lcl_vDebug, @"Cryptogram:%s",finalCT.c_str());

    // apply HMAC
    // TO DO

    NSString *cryptogram = [NSString stringWithUTF8String:finalCT.c_str()];

    return cryptogram;
}

- (NSString *)decryptUsingSerpentWithCiphertext:(NSString *)ciphertext andKey:(NSData *)keyData
{
    std::string ctext;
    std::string plaintext;

    byte key[ CryptoPP::Serpent::MAX_KEYLENGTH ], iv[ CryptoPP::Serpent::BLOCKSIZE ];

    ::memcpy(key, keyData.bytes, keyData.length);

    // decode from base64
    std::string encoded = [ciphertext UTF8String];

    // pull IV from ciphertext
    std::string ivs = encoded.substr(0,29);
    encoded.erase(0,29);

    CryptoPP::StringSource base64Decoder (encoded, true, new CryptoPP::Base64Decoder(new CryptoPP::StringSink(ctext)));

    std::string iv_tmp;
    CryptoPP::StringSource base64IVDecoder (ivs, true, new CryptoPP::Base64Decoder(new CryptoPP::StringSink(iv_tmp)));



    lcl_log(lcl_cCrypto, lcl_vDebug, @"Recovered IV[encoded]:%s",ivs.c_str());

    ::memcpy(iv, iv_tmp.data(), CryptoPP::Serpent::BLOCKSIZE);



    CryptoPP::Serpent::Decryption serpentDecryptor (key, CryptoPP::Serpent::MAX_KEYLENGTH);
    CryptoPP::CBC_Mode_ExternalCipher::Decryption cbcSerpentDecryptor (serpentDecryptor, iv);

    CryptoPP::StreamTransformationFilter stfSerpentDecryptor(cbcSerpentDecryptor, new CryptoPP::StringSink (plaintext), CryptoPP::StreamTransformationFilter::BlockPaddingScheme::ONE_AND_ZEROS_PADDING);
    stfSerpentDecryptor.Put( reinterpret_cast<const unsigned char*>( ctext.c_str() ), ctext.length());
    stfSerpentDecryptor.MessageEnd();

    NSString *plainText = [NSString stringWithUTF8String:plaintext.c_str()];

    return plainText;
}

我注意到 Base64 中的 IV 长度为 29 ...我不确定情况是否总是如此。是否可能是其他 16 字节 IV 的 base64 字符串的长度不同？

于 2013-12-02T10:40:03.153 回答