How to decrypt a signed pgp encrypted file?

Question

How can I decrypt and verify a file encrypted with PGP with the BouncyCastle Java API?

Answer 1

Encryption Code:

private static void encryptFile(OutputStream out, String fileName, PGPPublicKey encKey, PGPSecretKey pgpSec, boolean armor, boolean withIntegrityCheck, char[] pass) throws IOException, NoSuchProviderException {
    if (armor) {
        out = new ArmoredOutputStream(out);
    }

    try {
        PGPEncryptedDataGenerator encGen =
                new PGPEncryptedDataGenerator(
                new JcePGPDataEncryptorBuilder(PGPEncryptedData.CAST5).setWithIntegrityPacket(withIntegrityCheck).setSecureRandom(
                new SecureRandom())
                .setProvider("BC"));
        encGen.addMethod(new JcePublicKeyKeyEncryptionMethodGenerator(encKey).setProvider("BC"));
        OutputStream encryptedOut = encGen.open(out, new byte[BUFFER_SIZE]);

        PGPCompressedDataGenerator comData = new PGPCompressedDataGenerator(PGPCompressedData.ZIP);
        OutputStream compressedData = comData.open(encryptedOut);

        //OutputStream compressedData = encryptedOut;

        PGPPrivateKey pgpPrivKey = pgpSec.extractPrivateKey(
                new JcePBESecretKeyDecryptorBuilder().setProvider("BC").build(pass));
        PGPSignatureGenerator sGen = new PGPSignatureGenerator(new JcaPGPContentSignerBuilder(
                pgpSec.getPublicKey().getAlgorithm(), PGPUtil.SHA1).setProvider("BC"));
        sGen.init(PGPSignature.BINARY_DOCUMENT, pgpPrivKey);
        Iterator it = pgpSec.getPublicKey().getUserIDs();
        if (it.hasNext()) {
            PGPSignatureSubpacketGenerator spGen = new PGPSignatureSubpacketGenerator();
            spGen.setSignerUserID(false, (String) it.next());
            sGen.setHashedSubpackets(spGen.generate());
        }
        //BCPGOutputStream bOut = new BCPGOutputStream(compressedData);
        sGen.generateOnePassVersion(false).encode(compressedData); // bOut

        File file = new File(fileName);
        PGPLiteralDataGenerator lGen = new PGPLiteralDataGenerator();
        OutputStream lOut = lGen.open(compressedData, PGPLiteralData.BINARY, file.getName(), new Date(),
                                      new byte[BUFFER_SIZE]); //bOut
        FileInputStream fIn = new FileInputStream(file);
        int ch;

        while ((ch = fIn.read()) >= 0) {
            lOut.write(ch);
            sGen.update((byte) ch);
        }

        fIn.close();
        lOut.close();
        lGen.close();

        sGen.generate().encode(compressedData);

        //bOut.close();

        comData.close();
        compressedData.close();

        encryptedOut.close();
        encGen.close();

        if (armor) {
            out.close();
        }
    } catch (PGPException e) {
        System.err.println(e);
        if (e.getUnderlyingException() != null) {
            e.getUnderlyingException().printStackTrace();
        }
    } catch (SignatureException e) {
        System.err.println(e);
    }
}

Decryption Code:

public static void decryptFile(InputStream in, InputStream keyIn, char[] passwd, OutputStream fOut, InputStream publicKeyIn) throws IOException, NoSuchProviderException, SignatureException,
        PGPException {
    in = PGPUtil.getDecoderStream(in);

    PGPObjectFactory pgpF = new PGPObjectFactory(in);
    PGPEncryptedDataList enc;

    Object o = pgpF.nextObject();
    //
    // the first object might be a PGP marker packet.
    //
    if (o instanceof PGPEncryptedDataList) {
        enc = (PGPEncryptedDataList) o;
    } else {
        enc = (PGPEncryptedDataList) pgpF.nextObject();
    }

    //
    // find the secret key
    //
    Iterator<?> it = enc.getEncryptedDataObjects();
    PGPPrivateKey sKey = null;
    PGPPublicKeyEncryptedData pbe = null;
    PGPSecretKeyRingCollection pgpSec = new PGPSecretKeyRingCollection(PGPUtil.getDecoderStream(keyIn));

    while (sKey == null && it.hasNext()) {
        pbe = (PGPPublicKeyEncryptedData) it.next();
        sKey = PGPTools.findSecretKey(pgpSec, pbe.getKeyID(), passwd);
    }

    if (sKey == null) {
        throw new IllegalArgumentException("secret key for message not found.");
    }

    InputStream clear = pbe.getDataStream(
            new JcePublicKeyDataDecryptorFactoryBuilder().setProvider("BC").build(sKey));

    PGPObjectFactory plainFact = new PGPObjectFactory(clear);

    Object message = null;

    PGPOnePassSignatureList onePassSignatureList = null;
    PGPSignatureList signatureList = null;
    PGPCompressedData compressedData = null;

    message = plainFact.nextObject();
    ByteArrayOutputStream actualOutput = new ByteArrayOutputStream();

    while (message != null) {
        log.trace(message.toString());
        if (message instanceof PGPCompressedData) {
            compressedData = (PGPCompressedData) message;
            plainFact = new PGPObjectFactory(compressedData.getDataStream());
            message = plainFact.nextObject();
        }

        if (message instanceof PGPLiteralData) {
            // have to read it and keep it somewhere.
            Streams.pipeAll(((PGPLiteralData) message).getInputStream(), actualOutput);
        } else if (message instanceof PGPOnePassSignatureList) {
            onePassSignatureList = (PGPOnePassSignatureList) message;
        } else if (message instanceof PGPSignatureList) {
            signatureList = (PGPSignatureList) message;
        } else {
            throw new PGPException("message unknown message type.");
        }
        message = plainFact.nextObject();
    }
    actualOutput.close();
    PGPPublicKey publicKey = null;
    byte[] output = actualOutput.toByteArray();
    if (onePassSignatureList == null || signatureList == null) {
        throw new PGPException("Poor PGP. Signatures not found.");
    } else {

        for (int i = 0; i < onePassSignatureList.size(); i++) {
            PGPOnePassSignature ops = onePassSignatureList.get(0);
            log.trace("verifier : " + ops.getKeyID());
            PGPPublicKeyRingCollection pgpRing = new PGPPublicKeyRingCollection(
                    PGPUtil.getDecoderStream(publicKeyIn));
            publicKey = pgpRing.getPublicKey(ops.getKeyID());
            if (publicKey != null) {
                ops.init(new JcaPGPContentVerifierBuilderProvider().setProvider("BC"), publicKey);
                ops.update(output);
                PGPSignature signature = signatureList.get(i);
                if (ops.verify(signature)) {
                    Iterator<?> userIds = publicKey.getUserIDs();
                    while (userIds.hasNext()) {
                        String userId = (String) userIds.next();
                        log.trace("Signed by {}", userId);
                    }
                    log.trace("Signature verified");
                } else {
                    throw new SignatureException("Signature verification failed");
                }
            }
        }

    }

    if (pbe.isIntegrityProtected() && !pbe.verify()) {
        throw new PGPException("Data is integrity protected but integrity is lost.");
    } else if (publicKey == null) {
        throw new SignatureException("Signature not found");
    } else {
        fOut.write(output);
        fOut.flush();
        fOut.close();
    }
}

For reference, this is what PGPTools.findSecretKey does:

public static PGPPrivateKey findSecretKey(InputStream keyIn, long keyID, char[] pass)
        throws IOException, PGPException {
    PGPSecretKeyRingCollection pgpSec = new PGPSecretKeyRingCollection(PGPUtil.getDecoderStream(keyIn));
    PGPSecretKey pgpSecKey = pgpSec.getSecretKey(keyID);
    if (pgpSecKey == null) return null;

    PBESecretKeyDecryptor decryptor = new BcPBESecretKeyDecryptorBuilder(new BcPGPDigestCalculatorProvider()).build(pass);
    return pgpSecKey.extractPrivateKey(decryptor);
}