/**
* 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;
/**
* Common interface for all $(b-1)$-bit encodings of elements * of EdDSA finite fields. * @author str4d * */
public abstract class Encoding {
protected Field f;
public synchronized void setField(Field f) {
if (this.f != null)
throw new IllegalStateException("already set");
this.f = f;
}
/**
* Encode a FieldElement in its $(b-1)$-bit encoding.
* @param x the FieldElement to encode
* @return the $(b-1)$-bit encoding of this FieldElement.
*/
public abstract byte[] encode(FieldElement x);
/**
* Decode a FieldElement from its $(b-1)$-bit encoding.
* The highest bit is masked out.
* @param in the $(b-1)$-bit encoding of a FieldElement.
* @return the FieldElement represented by 'val'.
*/
public abstract FieldElement decode(byte[] in);
/**
* From the Ed25519 paper:<br>
* $x$ is negative if the $(b-1)$-bit encoding of $x$ is lexicographically larger
* than the $(b-1)$-bit encoding of -x. If $q$ is an odd prime and the encoding
* is the little-endian representation of $\{0, 1,\dots, q-1\}$ then the negative
* elements of $F_q$ are $\{1, 3, 5,\dots, q-2\}$.
* @param x the FieldElement to check
* @return true if negative
*/
public abstract boolean isNegative(FieldElement x);
}