Re: AES cbc? How to Init Openssl?

[Martin Salo]

Thanks to Marek and Bill :)

I have decided to use the EVP Aes version. This is my try. It worked fine for 
me.


Regards

Martin



#include <iostream>
#include <stdio.h>
#include <string.h>
#include <cmath>
#include <cstdlib>
#include <openssl/aes.h>
#include <openssl/evp.h>
#include <openssl/rand.h>


int AesEncrypt(const std::string &sAesKey,
                                        const std::string &ToEncrypt,
                                        std::string &Encrypted) {
        const int AesBlockSize=16;
        unsigned char cInitVector[AesBlockSize];
        EVP_CIPHER_CTX oEncCtx;
        const EVP_CIPHER *oChiper=0;
        int retval=0;
        unsigned char *cOutBuffer=0;
        
        // Set aes key:
        if (sAesKey.length()==16) {
                oChiper = EVP_aes_128_cbc();
        } else if (sAesKey.length()==32) {
                oChiper = EVP_aes_256_cbc();
        } else {
                return -1; // Wrong key size.
        }

        // Create init vector and add him infront of encrypted output data:
        RAND_pseudo_bytes(cInitVector, AesBlockSize);
        Encrypted.assign((char *)cInitVector, ((char 
*)cInitVector)+AesBlockSize);

        // Create encryption context.   
        EVP_CIPHER_CTX_init(&oEncCtx);
        EVP_EncryptInit_ex(&oEncCtx, oChiper, 0, (unsigned char 
*)sAesKey.c_str(), cInitVector);

        // Encrypt most of the data:
        int OutBufferByteLen = ToEncrypt.length()+2*AesBlockSize;
        cOutBuffer = new unsigned char[OutBufferByteLen];
        retval = EVP_EncryptUpdate(
                &oEncCtx,
                cOutBuffer,
                &OutBufferByteLen, 
                (unsigned char *)ToEncrypt.c_str(),
                ToEncrypt.length());

        // Doese encryption fail?
        if (retval<0) {
                delete[] cOutBuffer;
                return retval; // Encryption error.
        }

        // Add encrypted data to output:
        Encrypted.append((char *)cOutBuffer, ((char 
*)cOutBuffer)+OutBufferByteLen);
        delete[] cOutBuffer;
        
        //Add last block+padding:
        OutBufferByteLen = 2*AesBlockSize;
        cOutBuffer = new unsigned char[OutBufferByteLen]; // To be sure add two 
blocks.
        retval = EVP_EncryptFinal_ex(
                &oEncCtx,
                cOutBuffer,
                &OutBufferByteLen);

        // Doese encryption fail?
        if (retval<0) {
                delete[] cOutBuffer;
                return retval; // Encryption error.
        }

        // Add encrypted data to output:
        Encrypted.append((char *)cOutBuffer, ((char 
*)cOutBuffer)+OutBufferByteLen);
        delete[] cOutBuffer;

        EVP_CIPHER_CTX_cleanup(&oEncCtx);
        return 0; // Success
}

int AesDecrypt(const std::string &sAesKey,
                                        const std::string &ToDecrypt,
                                        std::string &Decrypted) {
        const int AesBlockSize=16;
        unsigned char cInitVector[AesBlockSize];
        EVP_CIPHER_CTX oEncCtx;
        const EVP_CIPHER *oChiper=0;
        int retval=0;
        unsigned char *cOutBuffer=0;
        
        // Set aes key:
        if (sAesKey.length()==16) {
                oChiper = EVP_aes_128_cbc();
        } else if (sAesKey.length()==32) {
                oChiper = EVP_aes_256_cbc();
        } else {
                return -1; // Wrong key size.
        }

        // Get init vector:
        const char *constInitVectorPtr = ToDecrypt.c_str();
        for (int i=0; i<AesBlockSize; i++) {
                cInitVector[i] = *constInitVectorPtr;
                constInitVectorPtr++;
        }

        // Create decryption context.   
        EVP_CIPHER_CTX_init(&oEncCtx);
        EVP_DecryptInit_ex(&oEncCtx, oChiper, 0, (unsigned char 
*)sAesKey.c_str(), cInitVector);

        // Decrypt most of the data:
        int OutBufferByteLen = ToDecrypt.length() - AesBlockSize; // Subtract 
the InitVec.
        cOutBuffer = new unsigned char[OutBufferByteLen];
        retval = EVP_DecryptUpdate(
                &oEncCtx,
                cOutBuffer,
                &OutBufferByteLen, 
                ((unsigned char *)ToDecrypt.c_str()) + AesBlockSize, // Remove 
the InitVector.
                OutBufferByteLen);

        // Doese encryption fail?
        if (retval<0) {
                delete[] cOutBuffer;
                return retval; // Encryption error.
        }

        // Add encrypted data to output:
        Decrypted.append((char *)cOutBuffer, ((char 
*)cOutBuffer)+OutBufferByteLen);
        delete[] cOutBuffer;
        
        //Add last block+padding:
        OutBufferByteLen = 2*AesBlockSize;
        cOutBuffer = new unsigned char[OutBufferByteLen]; // To be sure add two 
blocks.
        retval = EVP_DecryptFinal_ex(
                &oEncCtx,
                cOutBuffer,
                &OutBufferByteLen);

        // Doese encryption fail?
        if (retval<0) {
                delete[] cOutBuffer;
                return retval; // Encryption error.
        }

        // Add encrypted data to output:
        Decrypted.append((char *)cOutBuffer, ((char 
*)cOutBuffer)+OutBufferByteLen);
        delete[] cOutBuffer;

        EVP_CIPHER_CTX_cleanup(&oEncCtx);
        return 0; // Success
}

int main() {
        std::string ToEncrypt, Encrypted, Decrypted, AesKey;
        int retval=0;

        AesKey = "11111222223333344444555556666677"; // 32 Byte = 256 Bit key.
        ToEncrypt = 
"aaaaaaaaaaaaaabbbbbbbbbbbbbcccccccccccccccddddddddddddddddeeeeeeeeeeeeee";

        OpenSSL_add_all_algorithms();
        OpenSSL_add_all_ciphers();
        OpenSSL_add_all_digests();

        retval = AesEncrypt(AesKey, ToEncrypt, Encrypted);
        retval = AesDecrypt(AesKey, Encrypted, Decrypted);
        return 0;
}


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