x25519

Documentation

Overview

Package x25519 provides an implementation of the X25519 function, which performs scalar multiplication on the elliptic curve known as Curve25519. See RFC 7748.

Index

• Constants
• Variables
• func EdPrivateKeyToX25519(privateKey ed25519.PrivateKey) []byte
• func EdPublicKeyToX25519(publicKey ed25519.PublicKey) ([]byte, bool)
• func ScalarBaseMult(dst, in *[32]byte)
• func ScalarMult(dst, in, base *[32]byte)
• func X25519(scalar, point []byte) ([]byte, error)

Constants

const (
	// ScalarSize is the size of the scalar input to X25519.
	ScalarSize = 32
	// PointSize is the size of the point input to X25519.
	PointSize = 32
)

Variables

var Basepoint []byte

Basepoint is the canonical Curve25519 generator.

Functions

func EdPrivateKeyToX25519

func EdPrivateKeyToX25519(privateKey ed25519.PrivateKey) []byte

EdPrivateKeyToX25519 converts an Ed25519 private key into a corresponding X25519 private key such that the resulting X25519 public key will equal the result from EdPublicKeyToX25519.

func EdPublicKeyToX25519

func EdPublicKeyToX25519(publicKey ed25519.PublicKey) ([]byte, bool)

EdPublicKeyToX25519 converts an Ed25519 public key into the X25519 public key that would be generated from the same private key.

func ScalarBaseMult

func ScalarBaseMult(dst, in *[32]byte)

ScalarBaseMult sets dst to the product in*base where dst and base are the x coordinates of group points, base is the standard generator and all values are in little-endian form.

It is recommended to use the X25519 function with Basepoint instead, as copying into fixed size arrays can lead to unexpected bugs.

func ScalarMult

func ScalarMult(dst, in, base *[32]byte)

ScalarMult sets dst to the product in*base where dst and base are the x coordinates of group points and all values are in little-endian form.

Deprecated: when provided a low-order point, ScalarMult will set dst to all zeroes, irrespective of the scalar. Instead, use the X25519 function, which will return an error.

func X25519

func X25519(scalar, point []byte) ([]byte, error)

X25519 returns the result of the scalar multiplication (scalar * point), according to RFC 7748, Section 5. scalar, point and the return value are slices of 32 bytes.

scalar can be generated at random, for example with crypto/rand. point should be either Basepoint or the output of another X25519 call.

If point is Basepoint (but not if it's a different slice with the same contents) a precomputed implementation might be used for performance.