Package net.i2p.crypto.eddsa.math.bigint

Class BigIntegerLittleEndianEncoding

java.lang.Object

net.i2p.crypto.eddsa.math.Encoding

net.i2p.crypto.eddsa.math.bigint.BigIntegerLittleEndianEncoding

All Implemented Interfaces:

Serializable

public class BigIntegerLittleEndianEncoding
extends Encoding
implements Serializable

See Also:

Serialized Form

Field Summary

Fields inherited from class net.i2p.crypto.eddsa.math.Encoding

f

Constructor Summary

Constructors

Constructor	Description
BigIntegerLittleEndianEncoding()

Method Summary

Modifier and Type	Method	Description
FieldElement	decode(byte[] in)	Decode a FieldElement from its $(b-1)$-bit encoding.
byte[]	encode(BigInteger x)	Convert $x$ to little endian.
byte[]	encode(FieldElement x)	Encode a FieldElement in its $(b-1)$-bit encoding.
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)
BigInteger	toBigInteger(byte[] in)	Convert in to big endian

Methods inherited from class java.lang.Object

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

Constructor Detail

BigIntegerLittleEndianEncoding

public BigIntegerLittleEndianEncoding()

Method Detail

setField

public void setField(Field f)

Overrides:

setField in class Encoding

encode

public byte[] encode(FieldElement x)

Description copied from class: Encoding

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

Specified by:

encode in class Encoding

Parameters:

x - the FieldElement to encode

Returns:

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

encode

public byte[] encode(BigInteger x)

Convert $x$ to little endian. Constant time.

Parameters:

x - the BigInteger value to encode

Returns:

array of length $b/8$

Throws:

IllegalStateException - if field not set

decode

public FieldElement decode(byte[] in)

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

Specified by:

decode in class Encoding

Parameters:

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

Returns:

the FieldElement represented by 'val'.

Throws:

IllegalStateException - if field not set

IllegalArgumentException - if encoding is invalid

toBigInteger

public BigInteger toBigInteger(byte[] in)

Convert in to big endian

Parameters:

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

Returns:

the decoded value as a BigInteger

isNegative

public 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 $\{1, 3, 5,\dots, q-2\}$.

Specified by:

isNegative in class Encoding

Parameters:

x - the FieldElement to check

Returns:

true if negative