Encoding (I2P Anonymous Network - Java Documentation - Version 1.5.0)

java.lang.Object
- net.i2p.crypto.eddsa.math.Encoding

All Implemented Interfaces:

Serializable

Direct Known Subclasses:

BigIntegerLittleEndianEncoding, Ed25519LittleEndianEncoding
```
public abstract class Encoding
extends Object
implements Serializable
```
Common interface for all $(b-1)$-bit encodings of elements of EdDSA finite fields.

Since:

0.9.15

Author:

str4d

See Also:

Serialized Form

Field Summary

Fields
Modifier and Type Field Description

protected Field f

Constructor Summary

Constructors
Constructor Description

Encoding()

Method Summary

All Methods Instance Methods Abstract Methods Concrete Methods
Modifier and Type	Method	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