How to sign public PGP key with Bouncy Castle in Java

Question

I'm writing PGP server to generate keys for users.
I want to sign any generated PGP public key with my private key in Java with Bouncy Castle, to make it trusted for my users.

I have no problems with generating key pair - it works perfect.

I tried to sign by gpg --sign-key command line and it works good.

But I can't get the same in Java. I tried many solutions like this: java sign public pgp key with bouncycastle

and DirectKeySignature class from BC examples package, but nothing works for my.

Key is signed but gpg --check-sigs tell that signature is incorrect:

gpg --check-sigs "Adrian (test) <[email protected]>"
pub   4096R/9D5D4AB8 2018-06-20
sig-         E9798A8A 2018-08-04  Test (test) <[email protected]>
uid                  Adrian (test) <[email protected]>
sig!         9D5D4AB8 2018-06-20  Adrian (test) <[email protected]>

1 incorrect signature

Source code in two versions:

version 1:

public void signKey(String id, PGPSecretKey mySecretKey, PGPPublicKey publicKeyToBeSigned, char[] passPhrase, OutputStream out) throws PGPException, IOException {

    PGPPrivateKey pgpPrivKey = mySecretKey.extractPrivateKey(
            new JcePBESecretKeyDecryptorBuilder().setProvider(provider).build(passPhrase));

    PGPSignatureGenerator signatureGenerator = new PGPSignatureGenerator(
            new JcaPGPContentSignerBuilder(mySecretKey.getPublicKey().getAlgorithm(), PGPUtil.SHA1));

    signatureGenerator.init(PGPSignature.DIRECT_KEY, pgpPrivKey);

    PGPSignature signature = signatureGenerator.generateCertification(id, publicKeyToBeSigned);

    PGPPublicKey result = PGPPublicKey.addCertification(publicKeyToBeSigned, signature);

    out = new ArmoredOutputStream(out);

    result.encode(out);
    out.close();
}

version 2 (baset on org.bouncycastle.openpgp.examples.DirectKeySignature):

public void signPublicKey(PGPSecretKey secretKey, String secretKeyPass, PGPPublicKey keyToBeSigned, String notationName, String notationValue, OutputStream out) throws Exception {

    PGPPrivateKey pgpPrivKey = secretKey.extractPrivateKey(
            new JcePBESecretKeyDecryptorBuilder().setProvider("BC").build(secretKeyPass.toCharArray()));

    PGPSignatureGenerator sGen = new PGPSignatureGenerator(
            new JcaPGPContentSignerBuilder(secretKey.getPublicKey().getAlgorithm(), PGPUtil.SHA1).setProvider("BC"));

    sGen.init(PGPSignature.DIRECT_KEY, pgpPrivKey);

    PGPSignatureSubpacketGenerator spGen = new PGPSignatureSubpacketGenerator();

    boolean isHumanReadable = true;

    spGen.setNotationData(true, isHumanReadable, notationName, notationValue);

    PGPSignatureSubpacketVector packetVector = spGen.generate();

    sGen.setHashedSubpackets(packetVector);

    PGPPublicKey result = PGPPublicKey.addCertification(keyToBeSigned, sGen.generate());

    out = new ArmoredOutputStream(out);

    result.encode(out);
    out.close();
}

Test:

@Test
public void signKey() throws Exception {

    FileInputStream in = new FileInputStream("src/test/resources/secret.dat");

    PgpServiceImpl pgp = new PgpServiceImpl();

    PGPSecretKey pgpSecretKey = pgp.readSecretKey(in, "..........".toCharArray());
    PGPPublicKey pubKey = pgp.readPublicKey(new FileInputStream("src/test/resources/pub_other.dat"));

    ByteArrayOutputStream res = new ByteArrayOutputStream();

    pgp.signPublicKey(pgpSecretKey, "..........", pubKey, "Test (test) <[email protected]>", "Adrian (test) <[email protected]>", res);

    System.out.println(new String(res.toByteArray()));
}

result:

Please edit your question to include the full source code you have so we can test it, as described on stackoverflow.com/help/mcve. — Progman

Adrian Lapierre Adrian Lapierre · Accepted Answer · 2018-08-30T19:00:11

this works perfectly:

public void signPublicKey(PGPSecretKey secretKey, char[] passPhrase, PGPPublicKey keyToBeSigned, OutputStream out) throws PGPException, IOException {

        PGPPrivateKey pgpPrivKey = secretKey.extractPrivateKey(
                new JcePBESecretKeyDecryptorBuilder().setProvider( provider )
                        .build(passPhrase));

        PGPSignatureGenerator signatureGenerator = new PGPSignatureGenerator(
                new JcaPGPContentSignerBuilder( secretKey.getPublicKey().getAlgorithm(), PGPUtil.SHA1 ) );

        signatureGenerator.init( PGPSignature.DEFAULT_CERTIFICATION, pgpPrivKey );

        Iterator<String> ids = keyToBeSigned.getUserIDs();
        if(!ids.hasNext()) throw new IllegalArgumentException("klucz nie posiada żadnego User ID");
        String id = ids.next();

        PGPSignature signature = signatureGenerator.generateCertification(id, keyToBeSigned);
        PGPPublicKey newKey = PGPPublicKey.addCertification(keyToBeSigned, id, signature);

        out = new ArmoredOutputStream(out);

        newKey.encode(out);
        out.close();
    }

How to sign public PGP key with Bouncy Castle in Java

1 Answers