Unicode C

Decrypt File in Chunks using 256-bit AES

See more Encryption Examples

Shows how to decrypt a file chunk-by-chunk using FirstChunk/LastChunk properties and accumulate the results in memory with a Chilkat BinData object. Unicode C

#include <C_CkCrypt2W.h>
#include <C_CkFileAccessW.h>
#include <C_CkBinDataW.h>

void ChilkatSample(void)
    {
    BOOL success;
    HCkCrypt2W crypt;
    const wchar_t *fileToDecrypt;
    HCkFileAccessW facIn;
    int chunkSize;
    int numChunks;
    HCkBinDataW bd;
    HCkBinDataW bdDecrypted;
    int i;

    success = FALSE;

    //  This example assumes the Chilkat API to have been previously unlocked.
    //  See Global Unlock Sample for sample code.

    //  This example decrypts the file previously encrypted in this example:
    //  Encrypt File in Chunks using AES CBC

    crypt = CkCrypt2W_Create();

    CkCrypt2W_putCryptAlgorithm(crypt,L"aes");
    CkCrypt2W_putCipherMode(crypt,L"cbc");
    CkCrypt2W_putKeyLength(crypt,256);

    CkCrypt2W_SetEncodedKey(crypt,L"000102030405060708090A0B0C0D0E0F000102030405060708090A0B0C0D0E0F",L"hex");
    CkCrypt2W_SetEncodedIV(crypt,L"000102030405060708090A0B0C0D0E0F",L"hex");

    fileToDecrypt = L"c:/temp/qa_output/hamlet.enc";
    facIn = CkFileAccessW_Create();
    success = CkFileAccessW_OpenForRead(facIn,fileToDecrypt);
    if (success != TRUE) {
        wprintf(L"Failed to open file to be decrytped.\n");
        CkCrypt2W_Dispose(crypt);
        CkFileAccessW_Dispose(facIn);
        return;
    }

    //  Let's decrypt in 32000 byte chunks.
    chunkSize = 32000;
    numChunks = CkFileAccessW_GetNumBlocks(facIn,chunkSize);

    CkCrypt2W_putFirstChunk(crypt,TRUE);
    CkCrypt2W_putLastChunk(crypt,FALSE);

    bd = CkBinDataW_Create();
    bdDecrypted = CkBinDataW_Create();

    i = 0;
    while (i < numChunks) {
        i = i + 1;
        if (i == numChunks) {
            CkCrypt2W_putLastChunk(crypt,TRUE);
        }

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

        //  Decrypt this chunk.
        CkCrypt2W_DecryptBd(crypt,bd);
        //  Accumulate the decrypted chunks.
        CkBinDataW_AppendBd(bdDecrypted,bd);

        CkCrypt2W_putFirstChunk(crypt,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.
    CkCrypt2W_putFirstChunk(crypt,TRUE);
    CkCrypt2W_putLastChunk(crypt,TRUE);

    CkFileAccessW_FileClose(facIn);

    //  The fully decrypted file is contained in bdDecrypted.
    //  You can save to a file if desired, or use the decrypted data in your application directly from bdDecrypted.
    CkBinDataW_WriteFile(bdDecrypted,L"c:/temp/qa_output/hamlet_decrypted.xml");


    CkCrypt2W_Dispose(crypt);
    CkFileAccessW_Dispose(facIn);
    CkBinDataW_Dispose(bd);
    CkBinDataW_Dispose(bdDecrypted);

    }