(C# UWP/WinRT) 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 Universal Windows Platform (UWP) / WinRT Downloads Chilkat for the Universal Windows Platform (UWP)

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

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

crypt.CryptAlgorithm = "aes";
crypt.CipherMode = "cbc";
crypt.KeyLength = 128;

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

string fileToEncrypt = "qa_data/hamlet.xml";
Chilkat.FileAccess facIn = new Chilkat.FileAccess();
bool success = facIn.OpenForRead(fileToEncrypt);
if (success != true) {
    Debug.WriteLine("Failed to open file that is to be encrytped.");
    return;
}

string outputEncryptedFile = "qa_output/hamlet.enc";
Chilkat.FileAccess facOutEnc = new Chilkat.FileAccess();
success = facOutEnc.OpenForWrite(outputEncryptedFile);
if (success != true) {
    Debug.WriteLine("Failed to encrypted output file.");
    return;
}

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

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

Chilkat.BinData bd = 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);

    // Encrypt.
    crypt.EncryptBd(bd);

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

    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();
facOutEnc.FileClose();

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

// Compare the contents of the decrypted file with the original file:
bool bSame = facIn.FileContentsEqual(fileToEncrypt,decryptedFile);
Debug.WriteLine("bSame = " + Convert.ToString(bSame));