Fix NPEs and expose decryption keys

pgpainless-core/src/main/java/org/pgpainless/decryption_verification/MessageMetadata.java

@@ -7,6 +7,7 @@ package org.pgpainless.decryption_verification;
 import org.pgpainless.algorithm.CompressionAlgorithm;
 import org.pgpainless.algorithm.StreamEncoding;
 import org.pgpainless.algorithm.SymmetricKeyAlgorithm;
+import org.pgpainless.key.SubkeyIdentifier;
 import org.pgpainless.util.SessionKey;
 
 import javax.annotation.Nonnull;
@@ -182,6 +183,24 @@ public class MessageMetadata {
         return (LiteralData) nested;
     }
 
+    public SubkeyIdentifier getDecryptionKey() {
+        Iterator<SubkeyIdentifier> iterator = new LayerIterator<SubkeyIdentifier>(message) {
+            @Override
+            public boolean matches(Nested layer) {
+                return layer instanceof EncryptedData;
+            }
+
+            @Override
+            public SubkeyIdentifier getProperty(Layer last) {
+                return ((EncryptedData) last).decryptionKey;
+            }
+        };
+        if (iterator.hasNext()) {
+            return iterator.next();
+        }
+        return null;
+    }
+
     public abstract static class Layer {
         protected final List<SignatureVerification> verifiedDetachedSignatures = new ArrayList<>();
         protected final List<SignatureVerification.Failure> rejectedDetachedSignatures = new ArrayList<>();
@@ -309,6 +328,7 @@ public class MessageMetadata {
 
     public static class EncryptedData extends Layer implements Nested {
         protected final SymmetricKeyAlgorithm algorithm;
+        protected SubkeyIdentifier decryptionKey;
         protected SessionKey sessionKey;
         protected List<Long> recipients;
 

pgpainless-core/src/main/java/org/pgpainless/decryption_verification/OpenPgpMessageInputStream.java

@@ -334,6 +334,7 @@ public class OpenPgpMessageInputStream extends DecryptionStream {
 
                 MessageMetadata.EncryptedData encryptedData = new MessageMetadata.EncryptedData(
                         SymmetricKeyAlgorithm.requireFromId(pkesk.getSymmetricAlgorithm(decryptorFactory)));
+                encryptedData.decryptionKey = new SubkeyIdentifier(decryptionKeys, decryptionKey.getKeyID());
                 encryptedData.sessionKey = sessionKey;
 
                 IntegrityProtectedInputStream integrityProtected = new IntegrityProtectedInputStream(decrypted, pkesk, options);
@@ -361,6 +362,7 @@ public class OpenPgpMessageInputStream extends DecryptionStream {
 
                     MessageMetadata.EncryptedData encryptedData = new MessageMetadata.EncryptedData(
                             SymmetricKeyAlgorithm.requireFromId(pkesk.getSymmetricAlgorithm(decryptorFactory)));
+                    encryptedData.decryptionKey = new SubkeyIdentifier(decryptionKeyCandidate.getA(), privateKey.getKeyID());
                     encryptedData.sessionKey = sessionKey;
 
                     IntegrityProtectedInputStream integrityProtected = new IntegrityProtectedInputStream(decrypted, pkesk, options);
@@ -560,8 +562,6 @@ public class OpenPgpMessageInputStream extends DecryptionStream {
         final List<PGPSignature> correspondingSignatures;
         boolean isLiteral = true;
 
-        final List<PGPSignature> verified = new ArrayList<>();
-
         private Signatures(ConsumerOptions options) {
             this.options = options;
             this.detachedSignatures = new ArrayList<>();
@@ -580,24 +580,33 @@ public class OpenPgpMessageInputStream extends DecryptionStream {
         void addDetachedSignature(PGPSignature signature) {
             long keyId = SignatureUtils.determineIssuerKeyId(signature);
             PGPPublicKeyRing certificate = findCertificate(keyId);
+
+            if (certificate != null) {
                 initialize(signature, certificate, keyId);
                 this.detachedSignatures.add(new DetachedOrPrependedSignature(signature, certificate, keyId));
             }
+        }
 
         void addPrependedSignature(PGPSignature signature) {
             long keyId = SignatureUtils.determineIssuerKeyId(signature);
             PGPPublicKeyRing certificate = findCertificate(keyId);
+
+            if (certificate != null) {
                 initialize(signature, certificate, keyId);
                 this.prependedSignatures.add(new DetachedOrPrependedSignature(signature, certificate, keyId));
             }
+        }
 
         void addOnePassSignature(PGPOnePassSignature signature) {
             PGPPublicKeyRing certificate = findCertificate(signature.getKeyID());
+
+            if (certificate != null) {
                 OnePassSignature ops = new OnePassSignature(signature, certificate, signature.getKeyID());
                 ops.init(certificate);
                 onePassSignatures.add(ops);
 
                 literalOPS.add(ops);
+            }
             if (signature.isContaining()) {
                 enterNesting();
             }
@@ -898,6 +907,7 @@ public class OpenPgpMessageInputStream extends DecryptionStream {
         resultBuilder.setFileName(m.getFilename());
         resultBuilder.setFileEncoding(m.getFormat());
         resultBuilder.setSessionKey(m.getSessionKey());
+        resultBuilder.setDecryptionKey(m.getDecryptionKey());
 
         for (SignatureVerification accepted : m.getVerifiedDetachedSignatures()) {
             resultBuilder.addVerifiedDetachedSignature(accepted);