React Native

Encrypt File in Chunks using AES CBC

See more Encryption Examples

Demonstrates how to use the FirstChunk/LastChunk properties to encrypt a file chunk-by-chunk. React Native

import { BinData, Crypt2, FileAccess } from '@chilkat/react-native'

async function chilkatExample() {
  // This example assumes the Chilkat API to have been previously unlocked.
  // See Global Unlock Sample for sample code.

  const crypt = new Crypt2();

  crypt.cryptAlgorithm = 'aes';
  crypt.cipherMode = 'cbc';
  crypt.keyLength = 256;

  crypt.setEncodedKey('000102030405060708090A0B0C0D0E0F000102030405060708090A0B0C0D0E0F', 'hex');
  crypt.setEncodedIV('000102030405060708090A0B0C0D0E0F', 'hex');

  const fileToEncrypt = 'qa_data/hamlet.xml';
  const facIn = new FileAccess();
  try {
    facIn.openForRead(fileToEncrypt);
  } catch {
    console.log('Failed to open file that is to be encrytped.');
    return;
  }

  const outputEncryptedFile = 'c:/temp/qa_output/hamlet.enc';
  const facOutEnc = new FileAccess();
  try {
    facOutEnc.openForWrite(outputEncryptedFile);
  } catch {
    console.log('Failed to encrypted output file.');
    return;
  }

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

  crypt.firstChunk = true;
  crypt.lastChunk = false;

  const bd = new BinData();

  let i = 0;
  while (i < numChunks) {
    i++;
    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:
  const decryptedFile = 'qa_output/hamlet_dec.xml';
  await crypt.ckDecryptFileAsync(outputEncryptedFile, decryptedFile);
  // Assume success for the example..

  // Compare the contents of the decrypted file with the original file:
  const bSame = facIn.fileContentsEqual(fileToEncrypt, decryptedFile);
  console.log(`bSame = ${bSame}`);
}