Node.js

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. Node.js

NODEJS_PRELUDE

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();