I am trying to get AES CBC decryption to produce the original input message as went into AES CBC encryption. I'm not getting it.

[AWell.1]

I have created a simple function to encrypt a message using the AES CBC flow suggested in the documentation (AES_CBC_Encrypt_Init, AES_CBC_Encrypt_Append, AES_CBC_Encrypt_Finish), and then using the same flow to decrypt (AES_CBC_Decrypt_Init, AES_CBC_Decrypt_Append, AES_CBC_Decrypt_Finish). I am using a fixed Key vector (32 bytes) and a fixed InitializationVector (16 bytes) and I'm using these same arrays in decryption as in encryption. But I don't get the original input message back.

Here is the code:

uint32_t doSimpleEncrypt()

{

 // AES context, error status and output length.

 AESCBCctx_stt AESctx;

 uint32_t   errorStatus  = AES_SUCCESS;

 int32_t    outputLength = 0;

 const uint8_t Plaintext[PLAINTEXT_LENGTH] = {0x61, 0x62, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68,

                        0x69, 0x6a, 0x6b, 0x6c, 0x6d, 0x6e, 0x6f, 0x70};

 uint32_t inputMessageLength = PLAINTEXT_LENGTH;

 /* Key to be used for AES encryption/decryption */

 uint8_t Key[CRL_AES256_KEY_SIZE] = {0x31,0x32,0x33,0x34,0x35,0x36,0x37,0x38,

                   0x31,0x32,0x33,0x34,0x35,0x36,0x37,0x38,

                   0x31,0x32,0x33,0x34,0x35,0x36,0x37,0x38,

                   0x31,0x32,0x33,0x34,0x35,0x36,0x37,0x38};

 /* Initialization Vector */

 uint8_t IV[CRL_AES_BLOCK] = {0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37, 0x38,

                0x39, 0x38, 0x37, 0x36, 0x35, 0x34, 0x33, 0x32};

 /* Buffer to store the output data */

 uint8_t OutputMessage[PLAINTEXT_LENGTH];

 /* Size of the output data */

 uint32_t OutputMessageLength = 0;

 /* Set flag field to default value */

 AESctx.mFlags = E_SK_DEFAULT;

 /* Set key size to 32 (corresponding to AES-256) */

 AESctx.mKeySize = CRL_AES256_KEY_SIZE;

 /* Set iv size field to IvLength*/

 AESctx.mIvSize = CRL_AES_BLOCK;

 errorStatus = AES_CBC_Encrypt_Init(&AESctx, &Key[0], &IV[0] );

 /* check for initialization errors */

 if (errorStatus == AES_SUCCESS)

 {

  /* Encrypt Data */

  errorStatus = AES_CBC_Encrypt_Append(&AESctx,Plaintext,inputMessageLength,OutputMessage,&outputLength);

  if (errorStatus == AES_SUCCESS){

   /* Write the number of data written*/

   OutputMessageLength = outputLength;

   /* Do the Finalization */

   errorStatus = AES_CBC_Encrypt_Finish(&AESctx, OutputMessage + OutputMessageLength, &outputLength);

   OutputMessageLength += outputLength;

   if(errorStatus == AES_SUCCESS){

    // now decrypt the encrypted message

    uint8_t decryptedMessage[PLAINTEXT_LENGTH];

    AESCBCctx_stt AESctx2;

    // Set flag field to default value.

    AESctx2.mFlags  = E_SK_DEFAULT;

    // Set the key size in AES status.

    AESctx2.mKeySize = CRL_AES256_KEY_SIZE;

    // Set the initialization vector size in AES status.

    AESctx2.mIvSize = CRL_AES_BLOCK;

    // Initialize the operation, by passing key and initialization vector.

    errorStatus = AES_CBC_Decrypt_Init(&AESctx2, &Key[0], &IV[0]);

    printAESctx(&AESctx2);

    // check for initialization errors.

    if (errorStatus == AES_SUCCESS)

    {

     // Decrypt Data in CBC mode.

     errorStatus = AES_CBC_Decrypt_Append(&AESctx2, OutputMessage, inputMessageLength, decryptedMessage, &outputLength);

     // check for decryption errors in CBC mode.

     if (errorStatus == AES_SUCCESS)

     {

      // Finalize data.

      OutputMessageLength = outputLength;

      errorStatus = AES_CBC_Decrypt_Finish(&AESctx2, (decryptedMessage + OutputMessageLength), &outputLength);

     }

     else {

      errorStatus = AES_ERR_BAD_OPERATION;

     }

    }

    else {

     errorStatus = AES_ERR_BAD_OPERATION;

    }

    sprintf(tmpStr,"decryptStatus: %d\r\n",(int)errorStatus);

    newDebugEvents->logEvent(tmpStr,EventPriorityEnum::devLevel);

    sprintf(tmpStr,"Beginning decryptedMessage\r\n");

    newDebugEvents->logEvent(tmpStr,EventPriorityEnum::devLevel);

    for(unsigned i=0; i<inputMessageLength; ++i){

     sprintf(tmpStr,"Decrypted[%d]: 0x%0x\r\n",i,(uint16_t)decryptedMessage[i]);

     newDebugEvents->logEvent(tmpStr,EventPriorityEnum::devLevel);

    }

    sprintf(tmpStr,"End decryptedMessage\r\n");

    newDebugEvents->logEvent(tmpStr,EventPriorityEnum::devLevel);

   }

  }

 }

 return errorStatus;

}

I have used the same input into some web-based AES CBC 256-bit key encryptor and decryptor, and it works there.