Minor - fix some small todo's

src/main/java/fr/xephi/authme/security/HashUtils.java

@@ -85,12 +85,22 @@ public final class HashUtils {
      * @param algorithm The algorithm to hash the message with
      * @return The digest in its hexadecimal representation
      */
-    private static String hash(String message, MessageDigestAlgorithm algorithm) {
-        MessageDigest md = getDigest(algorithm);
-        md.reset();
-        md.update(message.getBytes());
-        byte[] digest = md.digest();
+    public static String hash(String message, MessageDigest algorithm) {
+        algorithm.reset();
+        algorithm.update(message.getBytes());
+        byte[] digest = algorithm.digest();
         return String.format("%0" + (digest.length << 1) + "x", new BigInteger(1, digest));
     }
 
+    /**
+     * Hash the message with the given algorithm and return the hash in its hexadecimal notation.
+     *
+     * @param message The message to hash
+     * @param algorithm The algorithm to hash the message with
+     * @return The digest in its hexadecimal representation
+     */
+    private static String hash(String message, MessageDigestAlgorithm algorithm) {
+        return hash(message, getDigest(algorithm));
+    }
+
 }

src/main/java/fr/xephi/authme/security/crypts/RoyalAuth.java

@@ -1,14 +1,17 @@
 package fr.xephi.authme.security.crypts;
 
 import fr.xephi.authme.security.HashUtils;
+import fr.xephi.authme.security.MessageDigestAlgorithm;
+
+import java.security.MessageDigest;
 
 public class RoyalAuth extends UnsaltedMethod {
 
     @Override
     public String computeHash(String password) {
-        for (int i = 0; i < 25; i++) {
-            // TODO ljacqu 20151228: HashUtils#sha512 gets a new message digest each time...
-            password = HashUtils.sha512(password);
+        MessageDigest algorithm = HashUtils.getDigest(MessageDigestAlgorithm.SHA512);
+        for (int i = 0; i < 25; ++i) {
+            password = HashUtils.hash(password, algorithm);
         }
         return password;
     }