From c39d5a09ce029bdfced3da718aca029311266d6f Mon Sep 17 00:00:00 2001
From: Paul Schaub <vanitasvitae@fsfe.org>
Date: Tue, 12 Apr 2022 21:08:21 +0200
Subject: [PATCH] WIP: Fix fake signature issuer test

---
 .../consumer/SignatureValidator.java          | 34 ++++++++++++-------
 .../subpackets/SignatureSubpacketsUtil.java   | 25 ++++++++++++++
 2 files changed, 47 insertions(+), 12 deletions(-)

diff --git a/pgpainless-core/src/main/java/org/pgpainless/signature/consumer/SignatureValidator.java b/pgpainless-core/src/main/java/org/pgpainless/signature/consumer/SignatureValidator.java
index 51bfa7c3..e6c02ae0 100644
--- a/pgpainless-core/src/main/java/org/pgpainless/signature/consumer/SignatureValidator.java
+++ b/pgpainless-core/src/main/java/org/pgpainless/signature/consumer/SignatureValidator.java
@@ -59,13 +59,23 @@ public abstract class SignatureValidator {
             public void verify(PGPSignature signature) throws SignatureValidationException {
                 OpenPgpFingerprint signingKeyFingerprint = OpenPgpFingerprint.of(signingKey);
 
-                Long issuer = SignatureSubpacketsUtil.getIssuerKeyIdAsLong(signature);
-                if (issuer != null) {
-                    if (issuer != signingKey.getKeyID()) {
-                        throw new SignatureValidationException("Signature was not created by " + signingKeyFingerprint + " (signature issuer: " + Long.toHexString(issuer) + ")");
+                List<Long> issuers = SignatureSubpacketsUtil.getIssuerKeyIdsAsLongs(signature);
+                boolean match = false;
+                for (Long issuer : issuers) {
+                    if (issuer == 0L || issuer == signingKey.getKeyID()) {
+                        match = true;
+                        break;
                     }
                 }
 
+                if (!match) {
+                    String[] hex = new String[issuers.size()];
+                    for (int i = 0; i < hex.length; i++) {
+                        hex[i] = Long.toHexString(issuers.get(i));
+                    }
+                    throw new SignatureValidationException("Signature was not created by " + signingKeyFingerprint + " (signature issuers: " + Arrays.toString(hex) + ")");
+                }
+
                 OpenPgpFingerprint fingerprint = SignatureSubpacketsUtil.getIssuerFingerprintAsOpenPgpFingerprint(signature);
                 if (fingerprint != null) {
                     if (!fingerprint.equals(signingKeyFingerprint)) {
@@ -170,14 +180,14 @@ public abstract class SignatureValidator {
             @Override
             public void verify(PGPSignature signature) throws SignatureValidationException {
                 PublicKeyAlgorithm algorithm = PublicKeyAlgorithm.requireFromId(signingKey.getAlgorithm());
-                    int bitStrength = signingKey.getBitStrength();
-                    if (bitStrength == -1) {
-                        throw new SignatureValidationException("Cannot determine bit strength of signing key.");
-                    }
-                    if (!policy.getPublicKeyAlgorithmPolicy().isAcceptable(algorithm, bitStrength)) {
-                        throw new SignatureValidationException("Signature was made using unacceptable key. " +
-                                algorithm + " (" + bitStrength + " bits) is not acceptable according to the public key algorithm policy.");
-                    }
+                int bitStrength = signingKey.getBitStrength();
+                if (bitStrength == -1) {
+                    throw new SignatureValidationException("Cannot determine bit strength of signing key.");
+                }
+                if (!policy.getPublicKeyAlgorithmPolicy().isAcceptable(algorithm, bitStrength)) {
+                    throw new SignatureValidationException("Signature was made using unacceptable key. " +
+                            algorithm + " (" + bitStrength + " bits) is not acceptable according to the public key algorithm policy.");
+                }
             }
         };
     }
diff --git a/pgpainless-core/src/main/java/org/pgpainless/signature/subpackets/SignatureSubpacketsUtil.java b/pgpainless-core/src/main/java/org/pgpainless/signature/subpackets/SignatureSubpacketsUtil.java
index 9ebc03e8..46af9d6c 100644
--- a/pgpainless-core/src/main/java/org/pgpainless/signature/subpackets/SignatureSubpacketsUtil.java
+++ b/pgpainless-core/src/main/java/org/pgpainless/signature/subpackets/SignatureSubpacketsUtil.java
@@ -93,6 +93,21 @@ public final class SignatureSubpacketsUtil {
         return fingerprint;
     }
 
+    public static List<IssuerKeyID> getIssuerKeyIds(PGPSignature signature) {
+        List<IssuerKeyID> keyIds = getSignatureSubpackets(signature.getHashedSubPackets(), SignatureSubpacket.issuerKeyId);
+        keyIds.addAll(getSignatureSubpackets(signature.getUnhashedSubPackets(), SignatureSubpacket.issuerKeyId));
+        return keyIds;
+    }
+
+    public static List<Long> getIssuerKeyIdsAsLongs(PGPSignature signature) {
+        List<IssuerKeyID> keyIds = getIssuerKeyIds(signature);
+        List<Long> longs = new ArrayList<>();
+        for (IssuerKeyID keyID : keyIds) {
+            longs.add(keyID.getKeyID());
+        }
+        return longs;
+    }
+
     /**
      * Return the issuer key-id subpacket of the signature.
      * Since this packet is self-authenticating, we expect it to be in the unhashed area,
@@ -577,6 +592,16 @@ public final class SignatureSubpacketsUtil {
         return hashedSubpacket != null ? hashedSubpacket : unhashed(signature, type);
     }
 
+    public static <P extends org.bouncycastle.bcpg.SignatureSubpacket> List<P> getSignatureSubpackets(
+            PGPSignatureSubpacketVector vector, SignatureSubpacket type) {
+        List<P> subpackets = new ArrayList<>();
+        org.bouncycastle.bcpg.SignatureSubpacket[] fromVector = vector.getSubpackets(type.getCode());
+        for (org.bouncycastle.bcpg.SignatureSubpacket p : fromVector) {
+            subpackets.add((P) p);
+        }
+        return subpackets;
+    }
+
     /**
      * Return the last occurrence of a subpacket type in the given signature subpacket vector.
      *