net.i2p.crypto.eddsa.math

Class Encoding

java.lang.Object

net.i2p.crypto.eddsa.math.Encoding

Direct Known Subclasses:

BigIntegerLittleEndianEncoding, Ed25519LittleEndianEncoding

public abstract class Encoding
extends Object

Common interface for all $(b-1)$-bit encodings of elements of EdDSA finite fields.

Author:

str4d

Field Summary

Fields

Modifier and Type	Field and Description
protected Field	f

Constructor Summary

Constructors

Constructor and Description
Encoding()

Method Summary

Modifier and Type	Method and Description
abstract FieldElement	decode(byte[] in) Decode a FieldElement from its $(b-1)$-bit encoding.
abstract byte[]	encode(FieldElement x) Encode a FieldElement in its $(b-1)$-bit encoding.
abstract boolean	isNegative(FieldElement x) From the Ed25519 paper: $x$ is negative if the $(b-1)$-bit encoding of $x$ is lexicographically larger than the $(b-1)$-bit encoding of -x.
void	setField(Field f)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

f

protected Field f

Constructor Detail

Encoding

public Encoding()

Method Detail

setField

public void setField(Field f)

encode

public abstract byte[] encode(FieldElement x)

Encode a FieldElement in its $(b-1)$-bit encoding.

Parameters:

x - the FieldElement to encode

Returns:

the $(b-1)$-bit encoding of this FieldElement.

decode

public abstract FieldElement decode(byte[] in)

Decode a FieldElement from its $(b-1)$-bit encoding. The highest bit is masked out.

Parameters:

in - the $(b-1)$-bit encoding of a FieldElement.

Returns:

the FieldElement represented by 'val'.

isNegative

public abstract boolean isNegative(FieldElement x)

From the Ed25519 paper:
$x$ 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 $\{1, 3, 5,\dots, q-2\}$.

Parameters:

x - the FieldElement to check

Returns:

true if negative