Getting GPG Decryption To Work In Java (Bouncy Castle)

Question

let me start by saying I'm extremely new to all of this. What I am trying to do is to use gpg from within Java in order to decrypt an encrypted file.

What I've done successfully:

Had a colleague encrypt a file using my public key and his private key and successfully decrypted it.
Went the other way
Had another colleague try to decrypt a file that wasn't for him: fail (as expected)

My key was generated like this...

(gpg --version tells me I'm using 1.4.5 and I'm using Bouncy Castle 1.47)

gpg --gen-ley

Select option "DSA and Elgamal (default)"

Fill in the other fields and generate a key.

The file was encrypted using my public key and another's secret key. I want to decrypt it. I've written the following Java code to accomplish this. I'm using several deprecated methods, but I can't figure out how to properly implement the factory methods required to use the non-deprecated versions, so if anyone has an idea on implementations of those that I should be using that would be a nice bonus.

    Security.addProvider(new BouncyCastleProvider());

        PGPSecretKeyRingCollection secretKeyRing = new PGPSecretKeyRingCollection(new FileInputStream(new File("test-files/secring.gpg")));
        PGPSecretKeyRing pgpSecretKeyRing = (PGPSecretKeyRing) secretKeyRing.getKeyRings().next();
        PGPSecretKey secretKey = pgpSecretKeyRing.getSecretKey();
        PGPPrivateKey privateKey = secretKey.extractPrivateKey("mypassword".toCharArray(), "BC");

        System.out.println(privateKey.getKey().getAlgorithm());
        System.out.println(privateKey.getKey().getFormat());

        PGPObjectFactory pgpF = new PGPObjectFactory(
    new FileInputStream(new File("test-files/test-file.txt.gpg")));
        Object pgpObj = pgpF.nextObject();
        PGPEncryptedDataList encryptedDataList = (PGPEncryptedDataList) pgpObj;

        Iterator objectsIterator = encryptedDataList.getEncryptedDataObjects();

        PGPPublicKeyEncryptedData publicKeyEncryptedData = (PGPPublicKeyEncryptedData) objectsIterator.next();
        InputStream inputStream = publicKeyEncryptedData.getDataStream(privateKey, "BC");

So when I run this code I learn that my algorithm and format are as follows for my secret key:

Algorithm: DSA Format: PKCS#8

And then it breaks on the last line:

Exception in thread "main" org.bouncycastle.openpgp.PGPException: error setting asymmetric cipher
at org.bouncycastle.openpgp.operator.jcajce.JcePublicKeyDataDecryptorFactoryBuilder.decryptSessionData(Unknown Source)
at org.bouncycastle.openpgp.operator.jcajce.JcePublicKeyDataDecryptorFactoryBuilder.access$000(Unknown Source)
at org.bouncycastle.openpgp.operator.jcajce.JcePublicKeyDataDecryptorFactoryBuilder$2.recoverSessionData(Unknown Source)
at org.bouncycastle.openpgp.PGPPublicKeyEncryptedData.getDataStream(Unknown Source)
at org.bouncycastle.openpgp.PGPPublicKeyEncryptedData.getDataStream(Unknown Source)
at org.bouncycastle.openpgp.PGPPublicKeyEncryptedData.getDataStream(Unknown Source)
at org.bouncycastle.openpgp.PGPPublicKeyEncryptedData.getDataStream(Unknown Source)
at TestBouncyCastle.main(TestBouncyCastle.java:74)

Caused by: java.security.InvalidKeyException: unknown key type passed to ElGamal at org.bouncycastle.jcajce.provider.asymmetric.elgamal.CipherSpi.engineInit(Unknown Source) at org.bouncycastle.jcajce.provider.asymmetric.elgamal.CipherSpi.engineInit(Unknown Source) at javax.crypto.Cipher.init(DashoA13*..) at javax.crypto.Cipher.init(DashoA13*..) ... 8 more

I'm open to a lot of suggestions here, from "don't use gpg, use x instead" to "don't use bouncy castle, use x instead" to anything in between. Thanks!

score 17 · Answer 1 · answered Oct 19 '15 at 13:53

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());
        }

This is year 2018 ! I have a question. I am encrypting an .xlsx file(Bank_21_05_2018.xlsx). The output file looks same as the original file (same name) but now I am not able to open it. Was the filename supposed to be Bank_21_05_2018.gpg on its own ? I am new to PGP — Black Diamond, May 31 '18 at 18:13

score 4 · Answer 2 · edited May 23 '17 at 12:17

4

To any one looking for an alternative solution, see https://stackoverflow.com/a/42176529/7550201

final InputStream plaintextStream = BouncyGPG
           .decryptAndVerifyStream()
           .withConfig(keyringConfig)
           .andRequireSignatureFromAllKeys("sender@example.com")
           .fromEncryptedInputStream(cipherTextStream)

Long story short: Bouncycastle is programming is often a lot of cargo cult programming and I wrote a library to change that.

edited May 23 '17 at 12:17

Community

1
1

answered Feb 11 '17 at 13:50

Jens

570
3
11

Can I use this library to decrypt just using private key? – Rocky4Ever Jul 15 '20 at 23:03

score 3 · Accepted Answer · edited May 23 '17 at 12:32

I've decided to go with a much different approach, which is to forego the use of bouncy castle altogether and simply use a runtime process instead. For me this solution is working and completely removes the complexity surrounding bouncy castle:

String[] gpgCommands = new String[] {
        "gpg",
        "--passphrase",
        "password",
        "--decrypt",
        "test-files/accounts.txt.gpg"
};

Process gpgProcess = Runtime.getRuntime().exec(gpgCommands);
BufferedReader gpgOutput = new BufferedReader(new InputStreamReader(gpgProcess.getInputStream()));
BufferedReader gpgError = new BufferedReader(new InputStreamReader(gpgProcess.getErrorStream()));

After doing that you need to remember to drain your input stream as your process is execing or your program will probably hang depending on how much you're outputing. See my answer in this thread (and also that of Cameron Skinner and Matthew Wilson who got me on the proper path) for a bit more context: Calling GnuPG in Java via a Runtime Process to encrypt and decrypt files - Decrypt always hangs

-1 For the obvious reasons. Also, your passphrase may be visible to anyone looking at the list of active processes, during the call, and may also end up in the system log. — user359996, May 21 '13 at 18:00

score 1 · Answer 4 · answered Feb 21 '13 at 02:35

1

The first Google result is this. It looks like you are trying to decrypt ElGamal data, but you are not passing in an ElGamal key.

There are two easy possibilities:

Your keyring collection has multiple keyrings.
Your keyring has subkeys.

You've picked DSA with ElGamal encryption, so I suspect at least the latter: Subkeys are signed by the master key; ElGamal is not a signing algorithm (I don't know if DSA and ElGamal can use the same key, but it's generally seen as a good idea to use different keys for different purposes).

I think you want something like this (also, secretKeyRing should probably be renamed to secretKeyRingCollection):

PGPSecretKey secretKey = secretKeyRing.getSecretKey(publicKeyEncryptedData.getKeyID());

answered Feb 21 '13 at 02:35

tc.

33,468
5
78
96

Thanks for the response. I agree on the naming. My key definitely has a sub key (at least when i look at it using gpg --list-keys). But I can certainly decrypt using it at command line. What's my hold up here? – Craig Feb 21 '13 at 03:17
Is the ElGamal key the subkey? – tc. Feb 21 '13 at 04:48
Hi tc. I've decided to go with a different approach for gpg decryption in java. I really appreciate the response but for me there is an easier solution which I will detail in an answer below. – Craig Feb 21 '13 at 14:10

chubbsondubs · Answer 5 · 2020-06-19T17:31:27.230

-1

The error message is difficult because it's not completely accurate. Besides the illegal key size or default parameters the exception doesn't says it could be failing because of crypto permission check fails. That means you haven't setup the JCE permissions properly. You'll need to install the JCE Unlimited Strength Policy.

You can see the debug messages by setting the system property on the jvm

java -Djava.security.debug=access ....

edited Jun 19 '20 at 17:31

answered Apr 03 '20 at 15:47

chubbsondubs

37,646
24
106
138

Why the down votes?! None of the other posts point out that you can actually see the underlying message by adding the java system property. If you do that then you'll get a more straightforward message that says you need to install the unlimited strength policy. I got that error and doing the above fixed it. – chubbsondubs Jun 19 '20 at 17:34
I didn't downvote but: the _nested_ exception (Caused by) is quite clear; _your_ case (old Java with limited policy) would always be 'InvalidKeyException: illegal key size' and never 'wrong key type'. Plus you're now quite late to the party; versions of Java since 8u161 in 2017 no longer have the limited-policy issue at all, as the better download page https://www.oracle.com/java/technologies/javase-jce-all-downloads.html explains. – dave_thompson_085 Aug 11 '20 at 11:57
I don't think that message is very clear at all. I suspect many others won't find it helpful either. Someone could always ask for an illegal key size that is not supported and get that message and it has nothing to do with the policy restrictions. Late or not, none of the other answers explained how to get a more straight forward error message which is helpful when debugging things after you believe you've installed it. – chubbsondubs Aug 23 '20 at 14:01

Getting GPG Decryption To Work In Java (Bouncy Castle)

5 Answers5

Linked