使用openssl解密AES-GCM文件

Question

I'm currently trying to decrypt a given text using openssl. I tried to make my own code using the example given there : Late authentication in OpenSSL GCM decryption but i still have a bad result in the end. My decryption function is as followed :

void aes_decrypt(EVP_CIPHER_CTX ctx, unsigned char *pCipherText,
    int pCipherTextLen, int AADLen, unsigned char* pKey, unsigned char* pIv,
    unsigned char* pMac, int MacLen) {
int bytesProcessed = 12;
int dec_success;

}
unsigned char * pOut = malloc(pCipherTextLen);
unsigned char * pAAD = malloc(AADLen);
unsigned char * pClearText = malloc(pCipherTextLen);

// setting cipher, key and iv
EVP_DecryptInit(&ctx, EVP_aes_256_gcm(), pKey, pIv);
// setting tag
EVP_CIPHER_CTX_ctrl(&ctx, EVP_CTRL_GCM_SET_IVLEN, 24, NULL);
EVP_CIPHER_CTX_ctrl(&ctx, EVP_CTRL_GCM_SET_TAG, 16, pMac);
// adding Additional Authenticated Data (AAD)
EVP_DecryptUpdate(&ctx, NULL, &bytesProcessed, pAAD, AADLen);
// decrypting data
EVP_DecryptUpdate(&ctx, pClearText, &bytesProcessed, pCipherText,
        pCipherTextLen);
// authentication step
dec_success = EVP_DecryptFinal(&ctx, pOut, &bytesProcessed);
free(pOut);
free(pMac);
free(pAAD);
free(pClearText);
}

All the data but the AAD are given previously by reading textfiles (I have a list of encrypted data, the key/Ivs used, the MAC and the result expected after decryption) After a few experiments, the following issues occures: - the result is diferent than the one expected - modifying the MAC doesn't affect the result (cleartext) - suppressing the AAD doesn't affect the results.

I realy doesn't know why it doesn't work. If you have any idea, tips or concret example, it would be a big help

Best regards

Answer 1

The problem is solved. The AAD provided by the program was wrong