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Experimental implementation of signing of existing hash contexts (MessageDigest instances)
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// SPDX-FileCopyrightText: 2022 Paul Schaub <vanitasvitae@fsfe.org>
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//
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// SPDX-License-Identifier: Apache-2.0
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package org.pgpainless.signature.builder;
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import java.io.IOException;
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import java.io.OutputStream;
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import java.security.MessageDigest;
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import org.bouncycastle.bcpg.PublicKeyAlgorithmTags;
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import org.bouncycastle.crypto.CipherParameters;
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import org.bouncycastle.crypto.CryptoException;
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import org.bouncycastle.crypto.DataLengthException;
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import org.bouncycastle.crypto.Digest;
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import org.bouncycastle.crypto.Signer;
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import org.bouncycastle.crypto.params.AsymmetricKeyParameter;
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import org.bouncycastle.crypto.params.Ed25519PrivateKeyParameters;
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import org.bouncycastle.crypto.params.Ed25519PublicKeyParameters;
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import org.bouncycastle.crypto.signers.DSADigestSigner;
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import org.bouncycastle.crypto.signers.DSASigner;
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import org.bouncycastle.crypto.signers.ECDSASigner;
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import org.bouncycastle.crypto.signers.Ed25519Signer;
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import org.bouncycastle.crypto.signers.Ed448Signer;
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import org.bouncycastle.crypto.signers.RSADigestSigner;
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import org.bouncycastle.openpgp.PGPException;
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import org.bouncycastle.openpgp.PGPPrivateKey;
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import org.bouncycastle.openpgp.operator.PGPContentSigner;
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import org.bouncycastle.openpgp.operator.PGPContentSignerBuilder;
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import org.bouncycastle.openpgp.operator.bc.BcPGPKeyConverter;
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import org.bouncycastle.util.Arrays;
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import org.pgpainless.algorithm.HashAlgorithm;
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import org.pgpainless.algorithm.PublicKeyAlgorithm;
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/**
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* Implementation of {@link PGPContentSignerBuilder} using the BC API, which can be used to sign hash contexts.
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* This can come in handy to sign data, which was already processed to calculate the hash context, without the
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* need to process it again to calculate the OpenPGP signature.
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*/
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public class HashContextPGPContentSignerBuilder implements PGPContentSignerBuilder {
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private final BcPGPKeyConverter keyConverter = new BcPGPKeyConverter();
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private final MessageDigest messageDigest;
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private final HashAlgorithm hashAlgorithm;
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public HashContextPGPContentSignerBuilder(MessageDigest messageDigest) {
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this.messageDigest = messageDigest;
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this.hashAlgorithm = HashAlgorithm.fromName(messageDigest.getAlgorithm());
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if (hashAlgorithm == null) {
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throw new IllegalArgumentException("Cannot recognize OpenPGP Hash Algorithm: " + messageDigest.getAlgorithm());
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}
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}
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@Override
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public PGPContentSigner build(int signatureType, PGPPrivateKey privateKey) throws PGPException {
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PublicKeyAlgorithm keyAlgorithm = PublicKeyAlgorithm.requireFromId(privateKey.getPublicKeyPacket().getAlgorithm());
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AsymmetricKeyParameter privKeyParam = keyConverter.getPrivateKey(privateKey);
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final Signer signer = createSigner(keyAlgorithm, messageDigest, privKeyParam);
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signer.init(true, privKeyParam);
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return new PGPContentSigner() {
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public int getType() {
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return signatureType;
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}
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public int getHashAlgorithm() {
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return hashAlgorithm.getAlgorithmId();
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}
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public int getKeyAlgorithm() {
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return keyAlgorithm.getAlgorithmId();
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}
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public long getKeyID() {
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return privateKey.getKeyID();
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}
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public OutputStream getOutputStream() {
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return new SignerOutputStream(signer);
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}
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public byte[] getSignature() {
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try {
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return signer.generateSignature();
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} catch (CryptoException e) {
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throw new IllegalStateException("unable to create signature");
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}
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}
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public byte[] getDigest() {
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return messageDigest.digest();
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}
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};
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}
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static Signer createSigner(
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PublicKeyAlgorithm keyAlgorithm,
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MessageDigest messageDigest,
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CipherParameters keyParam)
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throws PGPException {
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ExistingMessageDigest staticDigest = new ExistingMessageDigest(messageDigest);
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switch (keyAlgorithm.getAlgorithmId()) {
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case PublicKeyAlgorithmTags.RSA_GENERAL:
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case PublicKeyAlgorithmTags.RSA_SIGN:
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return new RSADigestSigner(staticDigest);
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case PublicKeyAlgorithmTags.DSA:
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return new DSADigestSigner(new DSASigner(), staticDigest);
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case PublicKeyAlgorithmTags.ECDSA:
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return new DSADigestSigner(new ECDSASigner(), staticDigest);
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case PublicKeyAlgorithmTags.EDDSA:
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if (keyParam instanceof Ed25519PrivateKeyParameters || keyParam instanceof Ed25519PublicKeyParameters) {
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return new EdDsaSigner(new Ed25519Signer(), staticDigest);
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}
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return new EdDsaSigner(new Ed448Signer(new byte[0]), staticDigest);
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default:
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throw new PGPException("cannot recognise keyAlgorithm: " + keyAlgorithm);
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}
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}
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static class ExistingMessageDigest implements Digest {
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private final MessageDigest digest;
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ExistingMessageDigest(MessageDigest messageDigest) {
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this.digest = messageDigest;
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}
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@Override
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public void update(byte in) {
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digest.update(in);
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}
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@Override
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public void update(byte[] in, int inOff, int len) {
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digest.update(in, inOff, len);
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}
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@Override
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public int doFinal(byte[] out, int outOff) {
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byte[] hash = digest.digest();
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System.arraycopy(hash, 0, out, outOff, hash.length);
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return getDigestSize();
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}
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@Override
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public void reset() {
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// Nope!
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// We cannot reset, since BCs signer classes are resetting in their init() methods, which would also reset
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// the messageDigest, losing its state. This would shatter our intention.
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}
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@Override
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public String getAlgorithmName() {
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return digest.getAlgorithm();
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}
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@Override
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public int getDigestSize() {
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return digest.getDigestLength();
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}
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}
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// Copied from BCs BcImplProvider - required since BCs class is package visible only :/
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private static class EdDsaSigner
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implements Signer {
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private final Signer signer;
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private final Digest digest;
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private final byte[] digBuf;
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EdDsaSigner(Signer signer, Digest digest) {
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this.signer = signer;
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this.digest = digest;
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this.digBuf = new byte[digest.getDigestSize()];
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}
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public void init(boolean forSigning, CipherParameters param) {
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this.signer.init(forSigning, param);
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this.digest.reset();
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}
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public void update(byte b) {
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this.digest.update(b);
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}
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public void update(byte[] in, int off, int len) {
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this.digest.update(in, off, len);
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}
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public byte[] generateSignature()
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throws CryptoException, DataLengthException {
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digest.doFinal(digBuf, 0);
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signer.update(digBuf, 0, digBuf.length);
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return signer.generateSignature();
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}
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public boolean verifySignature(byte[] signature) {
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digest.doFinal(digBuf, 0);
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signer.update(digBuf, 0, digBuf.length);
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return signer.verifySignature(signature);
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}
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public void reset() {
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Arrays.clear(digBuf);
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signer.reset();
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digest.reset();
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}
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}
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// Copied from BC, required since BCs class is package visible only
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static class SignerOutputStream
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extends OutputStream {
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private Signer sig;
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SignerOutputStream(Signer sig) {
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this.sig = sig;
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}
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public void write(byte[] bytes, int off, int len)
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throws IOException {
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sig.update(bytes, off, len);
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}
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public void write(byte[] bytes)
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throws IOException {
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sig.update(bytes, 0, bytes.length);
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}
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public void write(int b)
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throws IOException {
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sig.update((byte) b);
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}
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}
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}
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@ -0,0 +1,38 @@
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// SPDX-FileCopyrightText: 2022 Paul Schaub <vanitasvitae@fsfe.org>
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//
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// SPDX-License-Identifier: Apache-2.0
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package org.pgpainless.signature.builder;
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import java.security.MessageDigest;
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import org.bouncycastle.openpgp.PGPException;
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import org.bouncycastle.openpgp.PGPPrivateKey;
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import org.bouncycastle.openpgp.PGPSignature;
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import org.bouncycastle.openpgp.PGPSignatureGenerator;
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import org.pgpainless.algorithm.SignatureType;
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public class HashContextSigner {
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/**
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* Create an OpenPGP Signature over the given {@link MessageDigest} hash context.
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*
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* WARNING: This method does not yet validate the signing key.
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* TODO: Change API to receive and evaluate PGPSecretKeyRing + SecretKeyRingProtector instead.
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*
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* @param hashContext hash context
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* @param privateKey signing-capable key
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* @return signature
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* @throws PGPException in case of an OpenPGP error
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*/
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public static PGPSignature signHashContext(MessageDigest hashContext, SignatureType signatureType, PGPPrivateKey privateKey)
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throws PGPException {
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// TODO: Validate signing key
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PGPSignatureGenerator sigGen = new PGPSignatureGenerator(
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new HashContextPGPContentSignerBuilder(hashContext)
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);
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sigGen.init(signatureType.getCode(), privateKey);
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return sigGen.generate();
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}
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}
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