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. C#

bool 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

Chilkat.Crypt2 crypt = new Chilkat.Crypt2();

crypt.CryptAlgorithm = "aes";
crypt.CipherMode = "cbc";
crypt.KeyLength = 256;

crypt.SetEncodedKey("000102030405060708090A0B0C0D0E0F000102030405060708090A0B0C0D0E0F","hex");
crypt.SetEncodedIV("000102030405060708090A0B0C0D0E0F","hex");

string fileToDecrypt = "c:/temp/qa_output/hamlet.enc";
Chilkat.FileAccess facIn = new Chilkat.FileAccess();
success = facIn.OpenForRead(fileToDecrypt);
if (success != true) {
    Debug.WriteLine("Failed to open file to be decrytped.");
    return;
}

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

crypt.FirstChunk = true;
crypt.LastChunk = false;

Chilkat.BinData bd = new Chilkat.BinData();
Chilkat.BinData bdDecrypted = new Chilkat.BinData();

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

    //  Decrypt this chunk.
    crypt.DecryptBd(bd);
    //  Accumulate the decrypted chunks.
    bdDecrypted.AppendBd(bd);

    crypt.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.FirstChunk = true;
crypt.LastChunk = true;

facIn.FileClose();

//  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.
bdDecrypted.WriteFile("c:/temp/qa_output/hamlet_decrypted.xml");