(JavaScript) Decrypt File in Chunks using 256-bit AES

See more Encryption Examples

Note

This example is intended for running within a Chilkat.Js embedded JavaScript engine. All Chilkat JavaScript examples require Chilkat v11.4.0 or greater.

var 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

var crypt = new CkCrypt2();

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

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

var fileToDecrypt = "c:/temp/qa_output/hamlet.enc";
var facIn = new CkFileAccess();
success = facIn.OpenForRead(fileToDecrypt);
if (success !== true) {
    console.log("Failed to open file to be decrytped.");
    return;
}

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

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

var bd = new CkBinData();
var bdDecrypted = new CkBinData();

var 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");