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Getting BouncyCastle to decrypt a GPG-encrypted message

由 跟風遠走 提交于 2019-12-04 11:50:35

if anyone is interested to know how to encrypt and decrypt gpg files using bouncy castle openPGP library, check the below java code:

The below are the 4 methods you going to need:

The below method will read and import your secret key from .asc file:

public static PGPSecretKey readSecretKeyFromCol(InputStream in, long keyId) throws IOException, PGPException {
in = PGPUtil.getDecoderStream(in);
PGPSecretKeyRingCollection pgpSec = new PGPSecretKeyRingCollection(in, new BcKeyFingerprintCalculator());

PGPSecretKey key = pgpSec.getSecretKey(keyId);

if (key == null) {
    throw new IllegalArgumentException("Can't find encryption key in key ring.");
}
return key;
}

The below method will read and import your public key from .asc file:

@SuppressWarnings("rawtypes")
public static PGPPublicKey readPublicKeyFromCol(InputStream in) throws IOException, PGPException {
    in = PGPUtil.getDecoderStream(in);
    PGPPublicKeyRingCollection pgpPub = new PGPPublicKeyRingCollection(in, new BcKeyFingerprintCalculator());
    PGPPublicKey key = null;
    Iterator rIt = pgpPub.getKeyRings();
    while (key == null && rIt.hasNext()) {
        PGPPublicKeyRing kRing = (PGPPublicKeyRing) rIt.next();
        Iterator kIt = kRing.getPublicKeys();
        while (key == null && kIt.hasNext()) {
            PGPPublicKey k = (PGPPublicKey) kIt.next();
            if (k.isEncryptionKey()) {
                key = k;
            }
        }
    }
    if (key == null) {
        throw new IllegalArgumentException("Can't find encryption key in key ring.");
    }
    return key;
}

The below 2 methods to decrypt and encrypt gpg files:

public void decryptFile(InputStream in, InputStream secKeyIn, InputStream pubKeyIn, char[] pass) throws IOException, PGPException, InvalidCipherTextException {
    Security.addProvider(new BouncyCastleProvider());

    PGPPublicKey pubKey = readPublicKeyFromCol(pubKeyIn);

    PGPSecretKey secKey = readSecretKeyFromCol(secKeyIn, pubKey.getKeyID());

    in = PGPUtil.getDecoderStream(in);

    JcaPGPObjectFactory pgpFact;


    PGPObjectFactory pgpF = new PGPObjectFactory(in, new BcKeyFingerprintCalculator());

    Object o = pgpF.nextObject();
    PGPEncryptedDataList encList;

    if (o instanceof PGPEncryptedDataList) {

        encList = (PGPEncryptedDataList) o;

    } else {

        encList = (PGPEncryptedDataList) pgpF.nextObject();

    }

    Iterator<PGPPublicKeyEncryptedData> itt = encList.getEncryptedDataObjects();
    PGPPrivateKey sKey = null;
    PGPPublicKeyEncryptedData encP = null;
    while (sKey == null && itt.hasNext()) {
        encP = itt.next();
        secKey = readSecretKeyFromCol(new FileInputStream("PrivateKey.asc"), encP.getKeyID());
        sKey = secKey.extractPrivateKey(new BcPBESecretKeyDecryptorBuilder(new BcPGPDigestCalculatorProvider()).build(pass));
    }
    if (sKey == null) {
        throw new IllegalArgumentException("Secret key for message not found.");
    }

    InputStream clear = encP.getDataStream(new BcPublicKeyDataDecryptorFactory(sKey));

    pgpFact = new JcaPGPObjectFactory(clear);

    PGPCompressedData c1 = (PGPCompressedData) pgpFact.nextObject();

    pgpFact = new JcaPGPObjectFactory(c1.getDataStream());

    PGPLiteralData ld = (PGPLiteralData) pgpFact.nextObject();
    ByteArrayOutputStream bOut = new ByteArrayOutputStream();

    InputStream inLd = ld.getDataStream();

    int ch;
    while ((ch = inLd.read()) >= 0) {
        bOut.write(ch);
    }

    //System.out.println(bOut.toString());

    bOut.writeTo(new FileOutputStream(ld.getFileName()));
    //return bOut;

}

public static void encryptFile(OutputStream out, String fileName, PGPPublicKey encKey) throws IOException, NoSuchProviderException, PGPException {
    Security.addProvider(new BouncyCastleProvider());

    ByteArrayOutputStream bOut = new ByteArrayOutputStream();

    PGPCompressedDataGenerator comData = new PGPCompressedDataGenerator(PGPCompressedData.ZIP);

    PGPUtil.writeFileToLiteralData(comData.open(bOut), PGPLiteralData.BINARY, new File(fileName));

    comData.close();

    PGPEncryptedDataGenerator cPk = new PGPEncryptedDataGenerator(new BcPGPDataEncryptorBuilder(SymmetricKeyAlgorithmTags.TRIPLE_DES).setSecureRandom(new SecureRandom()));

    cPk.addMethod(new BcPublicKeyKeyEncryptionMethodGenerator(encKey));

    byte[] bytes = bOut.toByteArray();

    OutputStream cOut = cPk.open(out, bytes.length);

    cOut.write(bytes);

    cOut.close();

    out.close();
}

Now here is how to invoke/run the above:

try {
         decryptFile(new FileInputStream("encryptedFile.gpg"), new FileInputStream("PrivateKey.asc"), new FileInputStream("PublicKey.asc"), "yourKeyPassword".toCharArray());

        PGPPublicKey pubKey = readPublicKeyFromCol(new FileInputStream("PublicKey.asc"));

        encryptFile(new FileOutputStream("encryptedFileOutput.gpg"), "fileToEncrypt.txt", pubKey);




    } catch (PGPException e) {
        fail("exception: " + e.getMessage(), e.getUnderlyingException());
    }

It just means that content has been signed and then encrypted, the routine provided does not know how to deal with it, but at least tells you that. PGP protocol presents as a series of packets some of which can be wrapped in other ones (for example compressed data can also wrap signed data or simply literal data, these can be used to generate encrypted data as well, actual content always appears in literal data).

If you look at the verifyFile method in the SignedFileProcessor in the Bouncy Castle OpenPGP examples package you will see how to handle the signature data and get to the literal data containing the actual content.

I would also recommend looking at RFC 4880 so you have some idea of how the protocol works. The protocol is very loose and both GPG, BC, and the variety of products out there reflect this - that said the looseness does mean that if you try and cut and paste your way to a solution you'll end up with a disaster. It's not complicated, but understanding is required here as well.

标签
java
encryption
bouncycastle
public-key-encryption
gnupg
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