Java

Decrypt 256-bit AES GCM Produced by Something Unknown

See more Encryption Examples

Demonstrates how to decrypt something produced elsewhere (unknown) with 256-bit AES GCM. Chilkat2 Java

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

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.

        // We have the following to decrypt:

        // Key (Base64):
        String keyBase64 = "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx";

        // IV (Base64Url):
        String ivBase64Url = "xrvaINMLqotAbWRK";

        // ciphertext (base64url):
        String cipherBase64Url = "RtGNAS-zQOxSB8W0HfqJjCoyt9KgImW_l-HjVC40hOOl-RNfRF3hzDIT1kvFVF8i_KX9XmqAftb6lyq-jLCEc_MSgqt3q1ixv3Ez4SbS3G5e3qGzLwxIMi2sCt00aDNwK2ipsJ4aw8s7ePPnl4oY-y1st9rwCWR0rrgEZwS9jmS4uJWGPn9K3jbKRnMslznDbtFLNJctMVXBTP-cv47JelxLCBOQSlK29rMuEFrhHR_VQrPq6gtZaBVSXZSYT0XOklp7nu9mVhrMCRtBCC5oiu5MPE5JYx4ANo3hUY7_NyQl2bpn9GfRXrdvqRGE-gy2upj-cDkm0t_tV8xmYge9DBQTH3B_4BGl2qTk_o-m7pEmKkS8XSdQhGcuFlykqrkE8SzB5I8esfzWOM0pwxbz0H_VaylKYHY=";

        Crypt2 crypt = new Crypt2();

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

        crypt.setEncodedAad("random", "ascii");
        crypt.setEncodedKey(keyBase64, "base64");
        crypt.setEncodedIV(ivBase64Url, "base64url");

        // The cipher text contains the 16-byte auth tag at the end.
        // get it separately..
        BinData bdEncrypted = new BinData();
        BinData bdAuthTag = new BinData();
        bdEncrypted.appendEncoded(cipherBase64Url, "base64url");

        int numBytes = bdEncrypted.getNumBytes();
        String authTagHex = bdEncrypted.getEncodedChunk(numBytes - 16, 16, "hex");

        System.out.println("Auth tag in hex: " + authTagHex);

        bdAuthTag.appendEncoded(authTagHex, "hex");
        bdEncrypted.removeChunk(numBytes - 16, 16);

        // Use this special value to tell Chilkat to ignore the auth tag.
        crypt.setEncodedAuthTag("FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF", "hex");

        // Decrypt
        crypt.setEncodingMode("base64");
        String originalText = null;
        try {
            originalText = crypt.decryptStringENC(bdEncrypted.getEncoded("base64"));
            System.out.println(originalText);
            System.out.println("Success.");
        } catch (ChilkatException e) {
            System.out.println(e.getLastErrorText());
        }

        // Decrypted text
    }
}