Crypto: Throw checked exception

for unimplemented ElG import, so CertUtil.loadPrivateKey() will
continue processing and then
fail with the correct exception and error message on bad input.
Pull constant KeySpec out of loop.

core/java/src/net/i2p/crypto/CertUtil.java

@@ -349,9 +349,9 @@ public final class CertUtil {
                 throw new CertificateEncodingException("bad base64 cert");
             PrivateKey rv = null;
             // try all the types
+            KeySpec ks = new PKCS8EncodedKeySpec(data);
             for (SigAlgo algo : EnumSet.allOf(SigAlgo.class)) {
                 try {
-                    KeySpec ks = new PKCS8EncodedKeySpec(data);
                     String alg = algo.getName();
                     KeyFactory kf = KeyFactory.getInstance(alg);
                     rv = kf.generatePrivate(ks);

core/java/src/net/i2p/crypto/elgamal/impl/ElGamalPrivateKeyImpl.java

@@ -4,6 +4,7 @@ import java.io.IOException;
 import java.io.ObjectInputStream;
 import java.io.ObjectOutputStream;
 import java.math.BigInteger;
+import java.security.spec.InvalidKeySpecException;
 import java.security.spec.PKCS8EncodedKeySpec;
 
 import javax.crypto.interfaces.DHPrivateKey;
@@ -65,9 +66,9 @@ public class ElGamalPrivateKeyImpl
     }
 
     public ElGamalPrivateKeyImpl(
-        PKCS8EncodedKeySpec spec)
+        PKCS8EncodedKeySpec spec) throws InvalidKeySpecException
     {
-        throw new UnsupportedOperationException("todo");
+        throw new InvalidKeySpecException("todo");
         //this.x = spec.getX();
         //this.elSpec = new ElGamalParameterSpec(spec.getP(), spec.getG());
     }

core/java/src/net/i2p/crypto/elgamal/impl/ElGamalPublicKeyImpl.java

@@ -4,6 +4,7 @@ import java.io.IOException;
 import java.io.ObjectInputStream;
 import java.io.ObjectOutputStream;
 import java.math.BigInteger;
+import java.security.spec.InvalidKeySpecException;
 import java.security.spec.X509EncodedKeySpec;
 
 import javax.crypto.interfaces.DHPublicKey;
@@ -60,9 +61,9 @@ public class ElGamalPublicKeyImpl
     }
     
     public ElGamalPublicKeyImpl(
-        X509EncodedKeySpec spec)
+        X509EncodedKeySpec spec) throws InvalidKeySpecException
     {
-        throw new UnsupportedOperationException("todo");
+        throw new InvalidKeySpecException("todo");
         //this.y = y;
         //this.elSpec = elSpec;
     }