Fix parsing of legacy ed25519 keys with short MPIs

Author: vanitasvitae

pg/src/main/java/org/bouncycastle/openpgp/PGPSignature.java

@@ -495,18 +495,19 @@ else if (getKeyAlgorithm() == PublicKeyAlgorithmTags.EDDSA_LEGACY)
             {
                 byte[] a = BigIntegers.asUnsignedByteArray(sigValues[0].getValue());
                 byte[] b = BigIntegers.asUnsignedByteArray(sigValues[1].getValue());
-                if (a.length + b.length > Ed25519.SIGNATURE_SIZE)
-                {
-                    signature = new byte[Ed448.SIGNATURE_SIZE];
-                    System.arraycopy(a, 0, signature, Ed448.PUBLIC_KEY_SIZE - a.length, a.length);
-                    System.arraycopy(b, 0, signature, Ed448.SIGNATURE_SIZE - b.length, b.length);
-                }
-                else
+
+                if (a.length + b.length <= Ed25519.SIGNATURE_SIZE)
                 {
                     signature = new byte[Ed25519.SIGNATURE_SIZE];
                     System.arraycopy(a, 0, signature, Ed25519.PUBLIC_KEY_SIZE - a.length, a.length);
                     System.arraycopy(b, 0, signature, Ed25519.SIGNATURE_SIZE - b.length, b.length);
                 }
+                else
+                {
+                    signature = new byte[Ed448.SIGNATURE_SIZE];
+                    System.arraycopy(a, 0, signature, Ed448.PUBLIC_KEY_SIZE - a.length, a.length);
+                    System.arraycopy(b, 0, signature, Ed448.SIGNATURE_SIZE - b.length, b.length);
+                }
             }
             else
             {