bugfix: BaseMac would not use bsize in certain cases

The implementation of BaseMac would only take the bsize (size of the
hash) into account if the #doFinal(byte[], int) method was called.
Both other #doFinal methods would behave as if bsize==defbsize and
not cut the hash to the right size.

src/main/java/net/schmizz/sshj/transport/mac/BaseMAC.java

@@ -41,12 +41,12 @@ public class BaseMAC
 
     @Override
     public byte[] doFinal() {
-        return mac.doFinal();
+        return resizeToHashSize(mac.doFinal());
     }
 
     @Override
     public byte[] doFinal(byte[] input) {
-        return mac.doFinal(input);
+        return resizeToHashSize(mac.doFinal(input));
     }
 
     @Override
@@ -62,6 +62,15 @@ public class BaseMAC
         }
     }
 
+    private byte[] resizeToHashSize(byte[] buf) {
+        if (bsize == defbsize)
+            return buf;
+
+        byte[] result = new byte[bsize];
+        System.arraycopy(buf, 0, result, 0, bsize);
+        return result;
+    }
+
     @Override
     public int getBlockSize() {
         return bsize;