8029745: Enhance algorithm checking

Reviewed-by: mullan

src/share/classes/sun/security/provider/certpath/AlgorithmChecker.java

@@ -75,7 +75,7 @@ final public class AlgorithmChecker extends PKIXCertPathChecker {
     private PublicKey prevPubKey;
 
     private final static Set<CryptoPrimitive> SIGNATURE_PRIMITIVE_SET =
-                                    EnumSet.of(CryptoPrimitive.SIGNATURE);
+        Collections.unmodifiableSet(EnumSet.of(CryptoPrimitive.SIGNATURE));
 
     private final static DisabledAlgorithmConstraints
         certPathDefaultConstraints = new DisabledAlgorithmConstraints(

src/share/classes/sun/security/ssl/SignatureAndHashAlgorithm.java

@@ -68,7 +68,7 @@ final class SignatureAndHashAlgorithm {
 
     // performance optimization
     private final static Set<CryptoPrimitive> SIGNATURE_PRIMITIVE_SET =
-                                    EnumSet.of(CryptoPrimitive.SIGNATURE);
+        Collections.unmodifiableSet(EnumSet.of(CryptoPrimitive.SIGNATURE));
 
     // supported pairs of signature and hash algorithm
     private final static Map<Integer, SignatureAndHashAlgorithm> supportedMap;