Question

所以我试图在Objective-C项目中使用Crypto ++加密。关于如何处理IV的问题？我尝试将它预先附加到密文。但是我在恢复解密时遇到了问题。

以下是代码：

- (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;
}

注意我需要在预期的iv大小上加5才能获得完整的IV。然后我收到一个错误“无效的PCKS＃7填充发现。无效的密文”

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

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);

日志将在密文中显示仍有多个IV字节，并生成“无效密文，大小不是blockize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»ÓÃ”Ò¥ 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»ÓÃ”Ò¥ 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»ÓÃ”Ò¥ 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»ÓÃ”Ò¥ 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，在我尝试退出之后，部分IV仍然在密文之前。为什么会这样？

Answer 1

预先安排IV是完全正确的。为什么要在块大小中添加5？从Base-64解码为数据。将第一个BLOCKSIZE字节作为IV拉出。解密其余部分。

Answer 2

我设法解决了这个问题。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),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 ......我不确定总是这样......对于其他16字节IV，base64字符串的长度是不同的吗？

加密++如何处理IV

2 个答案: