Getting GPG Decryption To Work In Java (Bouncy Castle)
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!
Answer
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());
}