Add is_y_even method to ECPoint

Author: dufkan

JCMathLib/src/opencrypto/jcmathlib/ECPoint.java

@@ -468,6 +468,21 @@ private void from_x(Bignat x) {
         ech.unlock(ech.uncompressed_point_arr1);
     }
 
+    /**
+     * Returns true if Y coordinate is even; false otherwise.
+     *
+     * @return true if Y coordinate is even; false otherwise
+     */
+    public boolean is_y_even() {
+        ech.fnc_is_y.lock();
+        ech.lock(ech.uncompressed_point_arr1);
+        thePoint.getW(ech.uncompressed_point_arr1, (short) 0);
+        boolean result = ech.uncompressed_point_arr1[(short)(theCurve.POINT_SIZE - 1)] % 2 == 0;
+        ech.unlock(ech.uncompressed_point_arr1);
+        ech.fnc_is_y.unlock();
+        return result;
+    }
+
     /**
      * Compares this and provided point for equality. The comparison is made using hash of both values to prevent leak of position of mismatching byte.
      * @param other second point for comparison

JCMathLib/src/opencrypto/jcmathlib/ECPoint_Helper.java

@@ -15,7 +15,7 @@ public class ECPoint_Helper extends Base_Helper {
     public static final byte Signature_ALG_ECDSA_SHA_256 = (byte) 33;
 
     /**
-     * I true, fast multiplication of ECPoints via KeyAgreement can be used Is
+     * If true, fast multiplication of ECPoints via KeyAgreement can be used. Is
      * set automatically after successful allocation of required engines
      */
     public boolean FLAG_FAST_EC_MULT_VIA_KA = false;
@@ -45,6 +45,8 @@ public class ECPoint_Helper extends Base_Helper {
     Bignat fnc_from_x_y_sq;
     Bignat fnc_from_x_y;
 
+    Bignat fnc_is_y;
+
     KeyAgreement fnc_multiplication_x_keyAgreement;
     Signature    fnc_SignVerifyECDSA_signEngine; 
     MessageDigest fnc_isEqual_hashEngine;
@@ -92,6 +94,8 @@ void initialize() {
         Bignat fnc_from_x_y_sq;
         Bignat fnc_from_x_y;
 
+        fnc_is_y = rm.helperEC_BN_C;
+
         fnc_isEqual_hashArray = rm.helper_hashArray;
         fnc_isEqual_hashEngine = rm.hashEngine;