(MFC) Encrypt File in Chunks using AES CBC

Demonstrates how to use the FirstChunk/LastChunk properties to encrypt a file chunk-by-chunk.

Important This example requires Chilkat v9.5.0.68 or later.

Chilkat C/C++ Library Downloads MS Visual C/C++ Libs

See Also: Using MFC CString in Chilkat

#include <CkCrypt2.h>
#include <CkFileAccess.h>
#include <CkBinData.h>

void ChilkatSample(void)
    {
    CkString strOut;

    // This example requires the Chilkat Crypt API to have been previously unlocked.
    // See Unlock Chilkat Crypt for sample code.

    CkCrypt2 crypt;

    crypt.put_CryptAlgorithm("aes");
    crypt.put_CipherMode("cbc");
    crypt.put_KeyLength(128);

    crypt.SetEncodedKey("000102030405060708090A0B0C0D0E0F","hex");
    crypt.SetEncodedIV("000102030405060708090A0B0C0D0E0F","hex");

    const char *fileToEncrypt = "qa_data/hamlet.xml";
    CkFileAccess facIn;
    bool success = facIn.OpenForRead(fileToEncrypt);
    if (success != true) {
        strOut.append("Failed to open file that is to be encrytped.");
        strOut.append("\r\n");
        SetDlgItemText(IDC_EDIT1,strOut.getUnicode());
        return;
    }

    const char *outputEncryptedFile = "qa_output/hamlet.enc";
    CkFileAccess facOutEnc;
    success = facOutEnc.OpenForWrite(outputEncryptedFile);
    if (success != true) {
        strOut.append("Failed to encrypted output file.");
        strOut.append("\r\n");
        SetDlgItemText(IDC_EDIT1,strOut.getUnicode());
        return;
    }

    // Let's encrypt in 10000 byte chunks.
    int chunkSize = 10000;
    int numChunks = facIn.GetNumBlocks(chunkSize);

    crypt.put_FirstChunk(true);
    crypt.put_LastChunk(false);

    CkBinData bd;

    int i = 0;
    while (i < numChunks) {
        i = i + 1;
        if (i == numChunks) {
            crypt.put_LastChunk(true);
        }

        // Read the next chunk from the file.
        // The last chunk will be whatever amount remains in the file..
        bd.Clear();
        facIn.FileReadBd(chunkSize,bd);

        // Encrypt.
        crypt.EncryptBd(bd);

        // Write the encrypted chunk to the output file.
        facOutEnc.FileWriteBd(bd,0,0);

        crypt.put_FirstChunk(false);
    }

    // Make sure both FirstChunk and LastChunk are restored to true after
    // encrypting or decrypting in chunks.  Otherwise subsequent encryptions/decryptions
    // will produce unexpected results.
    crypt.put_FirstChunk(true);
    crypt.put_LastChunk(true);

    facIn.FileClose();
    facOutEnc.FileClose();

    // Decrypt the encrypted output file in a single call using CBC mode:
    const char *decryptedFile = "qa_output/hamlet_dec.xml";
    success = crypt.CkDecryptFile(outputEncryptedFile,decryptedFile);
    // Assume success for the example..

    // Compare the contents of the decrypted file with the original file:
    bool bSame = facIn.FileContentsEqual(fileToEncrypt,decryptedFile);
    strOut.append("bSame = ");
    strOut.appendInt(bSame);
    strOut.append("\r\n");


    SetDlgItemText(IDC_EDIT1,strOut.getUnicode());

    }