Java

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. Chilkat2 Java

import com.chilkatsoft.chilkat2.BinData;
import com.chilkatsoft.chilkat2.ChilkatException;
import com.chilkatsoft.chilkat2.Crypt2;
import com.chilkatsoft.chilkat2.FileAccess;

public class ChilkatExample {

    public static void main(String[] args) {
        // 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

        Crypt2 crypt = new Crypt2();

        crypt.setCryptAlgorithm("aes");
        crypt.setCipherMode("cbc");
        crypt.setKeyLength(256);

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

        String fileToDecrypt = "c:/temp/qa_output/hamlet.enc";
        FileAccess facIn = new FileAccess();
        try {
            facIn.openForRead(fileToDecrypt);
        } catch (ChilkatException e) {
            System.out.println("Failed to open file to be decrytped.");
            return;
        }

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

        crypt.setFirstChunk(true);
        crypt.setLastChunk(false);

        BinData bd = new BinData();
        BinData bdDecrypted = new BinData();

        int i = 0;
        while (i < numChunks) {
            i = i + 1;
            if (i == numChunks) {
                crypt.setLastChunk(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.setFirstChunk(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.setFirstChunk(true);
        crypt.setLastChunk(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");
    }
}