ScalarOps.java

/**
 * EdDSA-Java by str4d
 *
 * To the extent possible under law, the person who associated CC0 with
 * EdDSA-Java has waived all copyright and related or neighboring rights
 * to EdDSA-Java.
 *
 * You should have received a copy of the CC0 legalcode along with this
 * work. If not, see <https://creativecommons.org/publicdomain/zero/1.0/>.
 *
 */
package net.i2p.crypto.eddsa.math;

public interface ScalarOps {
    /**
     * Reduce the given scalar mod $l$.
     * <p>
     * From the Ed25519 paper:<br>
     * Here we interpret $2b$-bit strings in little-endian form as integers in
     * $\{0, 1,..., 2^{(2b)}-1\}$.
     * @param s the scalar to reduce
     * @return $s \bmod l$
     */
    public byte[] reduce(byte[] s);

    /**
     * $r = (a * b + c) \bmod l$
     * @param a a scalar
     * @param b a scalar
     * @param c a scalar
     * @return $(a*b + c) \bmod l$
     */
    public byte[] multiplyAndAdd(byte[] a, byte[] b, byte[] c);

    /**
     * Check, whether the given factor is valid and smaller than
     * the group order.
     *
     * @param s A little-endian encoded factor.
     * @return Whether <code>0 &le; s &lt; $l$</code>.
     */
    public boolean isValidFactor(byte[] s);
}