Prevent ClassCastException for v3 OpenPGP keys with non-RSA public keys

v3 and earlier OpenPGP keys can only use RSA as key algorithm.
This commit changes the behavior of BC to throw a PGPException instead of a ClassCastException when
encountering a malformed key.

Author: vanitasvitae

pg/src/main/java/org/bouncycastle/openpgp/operator/bc/BcKeyFingerprintCalculator.java

@@ -25,6 +25,10 @@ public byte[] calculateFingerprint(PublicKeyPacket publicPk)
 
         if (publicPk.getVersion() <= PublicKeyPacket.VERSION_3)
         {
+            if (!(key instanceof RSAPublicBCPGKey))
+            {
+                throw new PGPException("Version 3 OpenPGP keys can only use RSA. Found " + key.getClass().getName());
+            }
             RSAPublicBCPGKey rK = (RSAPublicBCPGKey)key;
 
             try

pg/src/main/java/org/bouncycastle/openpgp/operator/jcajce/JcaKeyFingerprintCalculator.java

@@ -66,6 +66,10 @@ public byte[] calculateFingerprint(PublicKeyPacket publicPk)
 
         if (publicPk.getVersion() <= PublicKeyPacket.VERSION_3)
         {
+            if (!(key instanceof RSAPublicBCPGKey))
+            {
+                throw new PGPException("Version 3 OpenPGP keys can only use RSA. Found " + key.getClass().getName());
+            }
             RSAPublicBCPGKey rK = (RSAPublicBCPGKey)key;
 
             try