Random IV from an encrypted file

[Rash]

Hello All,
      I encrypt a file using AES::CBC mode with a random IV. Something
like this

void encryptFile(const char* password, const char* inputFileName,
const char* outputFileName)
{
    byte pass[ AES::BLOCKSIZE ];        // digest of password
    byte iv[ AES::BLOCKSIZE ];                  // Initial Vector (IV)

    AutoSeededRandomPool *rng;
    rng = new AutoSeededRandomPool;             // random number generator

    // digest password
    delete new StringSource( password, true,
            new HashFilter(*(new SHA256), new ArraySink(pass,
AES::BLOCKSIZE)) );

    // random Initial Vector
    rng->GenerateBlock(iv, AES::BLOCKSIZE);

    // create object for encrypting
        AES::Encryption aesEncryption(pass,
CryptoPP::AES::DEFAULT_KEYLENGTH);
    CBC_Mode_ExternalCipher::Encryption cbcEncryption(aesEncryption,
iv);

        StreamTransformationFilter *encryptor;
    encryptor = new StreamTransformationFilter(cbcEncryption, new
FileSink(outputFileName) );

    // "bind" a file and encrypt one
    delete new FileSource(inputFileName, true, encryptor);
}

Now how do I get the same Initialization Vector (IV) to decrypt the
encrypted file or how do I write the decryptFile function:

void decryptFile(const char* password, const char*inputFileName,const
char* outputFileName)
{
      //how to get the IV that was used for encrypting the file.
    byte pass[ AES::BLOCKSIZE ];
    byte iv[ AES::BLOCKSIZE ];

    FileSource *source;
    try
        {
                source = new FileSource(inputFileName, false);

                delete new StringSource( password, true,
                new HashFilter(*(new SHA256), new
ArraySink(pass,AES::BLOCKSIZE)) );

                CryptoPP::AES::Decryption aesDecryption(pass,
CryptoPP::AES::DEFAULT_KEYLENGTH);
               CryptoPP::CBC_Mode_ExternalCipher::Decryption
cbcDecryption( aesDecryption, iv );

                // "bind" decryptor to output file
                source->Attach( new StreamTransformationFilter(cbcDecryption,
                                new FileSink((outputFileName) ) ));

                // push the rest data
                source->PumpAll();
        }
        catch(CryptoPP::Exception &e)
        {
                delete source ;
                throw;
        }
        delete source ;
}

The above decryptFile function doesnt decrypt the first block. I dont
know why?
Please help.

Please help as this is really important to me.
Thanks


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