(Node.js) Decrypt File in Chunks using 256-bit AES

See more Encryption Examples

Install Chilkat for Node.js and Electron using npm at Chilkat npm packages for Node.js Chilkat npm packages for Electron on Windows, Linux, MacOS

var os = require('os');
if (os.platform() == 'win32') {  
  var chilkat = require('@chilkat/ck-node23-win64'); 
} else if (os.platform() == 'linux') {
    if (os.arch() == 'arm') {
        var chilkat = require('@chilkat/ck-node23-linux-arm');
    } else if (os.arch() == 'arm64') {
        var chilkat = require('@chilkat/ck-node23-linux-arm64');
    } else {
        var chilkat = require('@chilkat/ck-node23-linux-x64');
    }
} else if (os.platform() == 'darwin') {
  var chilkat = require('@chilkat/ck-node23-mac-universal');
}

function chilkatExample() {

    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 chilkat.Crypt2();

    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 chilkat.FileAccess();
    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 chilkat.BinData();
    var bdDecrypted = new chilkat.BinData();

    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");

}

chilkatExample();