1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
|
/**
* 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);
}
|
