Used the O(1) equals. Moved bytesToHex function to Utils

Author: pmarches

src/net/i2p/crypto/eddsa/Utils.java

@@ -18,6 +18,18 @@ public static int equal(int b, int c) {
         return (result ^ 0x01) & 0x01;
     }
 
+    /**
+     * Constant-time byte[] comparison.
+     * @return 1 if b and c are equal, 0 otherwise.
+     */
+    public static int equal(byte[] b, byte[] c) {
+        int result = 0;
+        for (int i = 0; i < 32; i++) {
+            result |= b[i] ^ c[i];
+        }
+        return ~equal(result, 0) & 0x01;
+    }
+
     /**
      * Constant-time determine if byte is negative.
      * @param b the byte to check.
@@ -51,4 +63,22 @@ public static byte[] hexToBytes(String s) {
         }
         return data;
     }
+    
+    /**
+     * Converts bytes to a hex string.
+     * @param raw the byte[] to be converted.
+     * @return the hex representation as a string.
+     */
+    public static String bytesToHex(byte[] raw) {
+        if ( raw == null ) {
+            return null;
+        }
+        final StringBuilder hex = new StringBuilder(2 * raw.length);
+        for (final byte b : raw) {
+            hex.append(Character.forDigit((b & 0xF0) >> 4, 16))
+            .append(Character.forDigit((b & 0x0F), 16));
+        }
+        return hex.toString();
+    }
+
 }

src/net/i2p/crypto/eddsa/math/ed25519/Ed25519FieldElement.java

@@ -1,9 +1,6 @@
 package net.i2p.crypto.eddsa.math.ed25519;
 
-import java.util.Arrays;
-
-import javax.xml.bind.DatatypeConverter;
-
+import net.i2p.crypto.eddsa.Utils;
 import net.i2p.crypto.eddsa.math.Field;
 import net.i2p.crypto.eddsa.math.FieldElement;
 
@@ -29,11 +26,7 @@ public Ed25519FieldElement(Field f, int[] t) {
 
     public boolean isNonZero() {
         byte[] s = toByteArray();
-        int result = 0;
-        for (int i = 0; i < 32; i++) {
-            result |= s[i] ^ zero[i];
-        }
-        return result != 0;
+        return Utils.equal(s, zero) == 1;
     }
 
     /**
@@ -962,12 +955,11 @@ public boolean equals(Object obj) {
         if (!(obj instanceof Ed25519FieldElement))
             return false;
         Ed25519FieldElement fe = (Ed25519FieldElement) obj;
-        // TODO should this be constant time?
-        return Arrays.equals(toByteArray(), fe.toByteArray());
+        return 1==Utils.equal(toByteArray(), fe.toByteArray());
     }
 
     @Override
     public String toString() {
-        return "[Ed25519FieldElement val="+DatatypeConverter.printHexBinary(toByteArray())+"]";
+        return "[Ed25519FieldElement val="+Utils.bytesToHex(toByteArray())+"]";
     }
 }