net.arccotangent.pacchat.crypto.MsgCrypto.java Source code

Introduction

Here is the source code for net.arccotangent.pacchat.crypto.MsgCrypto.java

Source

/*
This file is part of PacChat.
    
PacChat is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
    
PacChat is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.
    
You should have received a copy of the GNU General Public License
along with PacChat.  If not, see <http://www.gnu.org/licenses/>.
*/

package net.arccotangent.pacchat.crypto;

import net.arccotangent.pacchat.logging.Logger;
import org.apache.commons.codec.binary.Base64;

import javax.crypto.SecretKey;
import javax.crypto.spec.SecretKeySpec;
import java.security.PrivateKey;
import java.security.PublicKey;

public class MsgCrypto {

    private static final Logger mc_log = new Logger("CRYPTO/MSGCRYPTO");

    public static String encryptAndSignMessage(String msg, PublicKey publicKey, PrivateKey privateKey) {
        mc_log.i("Encrypting and signing message.");
        SecretKey aes = AES.generateAESKey();

        assert aes != null;

        byte[] aesCryptedText = AES.encryptBytes(msg.getBytes(), aes);
        byte[] cryptedAesKey = RSA.encryptBytes(aes.getEncoded(), publicKey);

        byte[] signature = RSA.signBytes(cryptedAesKey, privateKey);

        String cryptedTextB64 = Base64.encodeBase64String(aesCryptedText);
        String cryptedKeyB64 = Base64.encodeBase64String(cryptedAesKey);
        String signatureB64 = Base64.encodeBase64String(signature);

        return cryptedKeyB64 + "\n" + cryptedTextB64 + "\n" + signatureB64;
    }

    public static PacchatMessage decryptAndVerifyMessage(String cryptedMsg, PrivateKey privateKey,
            PublicKey publicKey) {
        mc_log.i("Decrypting and verifying message.");
        String[] messageComponents = cryptedMsg.split("\n");
        String cryptedKeyB64 = messageComponents[0];
        String cryptedTextB64 = messageComponents[1];
        String signatureB64 = messageComponents[2];

        boolean verified = RSA.verifyBytes(Base64.decodeBase64(cryptedKeyB64), Base64.decodeBase64(signatureB64),
                publicKey);
        if (verified)
            mc_log.i("Message authenticity verified!");
        else {
            mc_log.w("**********************************************");
            mc_log.w("Message authenticity NOT VERIFIED! Will continue decryption anyway.");
            mc_log.w(
                    "Someone may be tampering with your connection! This is an unlikely, but not impossible scenario!");
            mc_log.w(
                    "If you are sure the connection was not tampered with, consider asking the sender to send out a key update.");
            mc_log.w("**********************************************");
        }

        DecryptStatus rsa = RSA.decryptBytes(Base64.decodeBase64(cryptedKeyB64), privateKey);
        byte[] aesKey = rsa.getMessage();
        SecretKey aes = new SecretKeySpec(aesKey, "AES");

        DecryptStatus message = AES.decryptBytes(Base64.decodeBase64(cryptedTextB64), aes);
        byte[] msg = message.getMessage();
        boolean decrypted = message.isDecryptedSuccessfully();

        return new PacchatMessage(new String(msg), verified, decrypted);
    }

}