90 lines
2.8 KiB
Go
90 lines
2.8 KiB
Go
// Copyright 2019 The Go Authors. All rights reserved.
|
|
// Use of this source code is governed by a BSD-style
|
|
// license that can be found in the LICENSE file.
|
|
|
|
// Package curve25519 provides an implementation of the X25519 function, which
|
|
// performs scalar multiplication on the elliptic curve known as Curve25519.
|
|
// See RFC 7748.
|
|
//
|
|
// This package is a wrapper for the X25519 implementation
|
|
// in the crypto/ecdh package.
|
|
package curve25519
|
|
|
|
import "crypto/ecdh"
|
|
|
|
// ScalarMult sets dst to the product scalar * point.
|
|
//
|
|
// 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 ScalarMult(dst, scalar, point *[32]byte) {
|
|
if _, err := x25519(dst, scalar[:], point[:]); err != nil {
|
|
// The only error condition for x25519 when the inputs are 32 bytes long
|
|
// is if the output would have been the all-zero value.
|
|
for i := range dst {
|
|
dst[i] = 0
|
|
}
|
|
}
|
|
}
|
|
|
|
// ScalarBaseMult sets dst to the product scalar * base where base is the
|
|
// standard generator.
|
|
//
|
|
// It is recommended to use the X25519 function with Basepoint instead, as
|
|
// copying into fixed size arrays can lead to unexpected bugs.
|
|
func ScalarBaseMult(dst, scalar *[32]byte) {
|
|
curve := ecdh.X25519()
|
|
priv, err := curve.NewPrivateKey(scalar[:])
|
|
if err != nil {
|
|
panic("curve25519: internal error: scalarBaseMult was not 32 bytes")
|
|
}
|
|
copy(dst[:], priv.PublicKey().Bytes())
|
|
}
|
|
|
|
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
|
|
)
|
|
|
|
// Basepoint is the canonical Curve25519 generator.
|
|
var Basepoint []byte
|
|
|
|
var basePoint = [32]byte{9}
|
|
|
|
func init() { Basepoint = basePoint[:] }
|
|
|
|
// 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.
|
|
func X25519(scalar, point []byte) ([]byte, error) {
|
|
// Outline the body of function, to let the allocation be inlined in the
|
|
// caller, and possibly avoid escaping to the heap.
|
|
var dst [32]byte
|
|
return x25519(&dst, scalar, point)
|
|
}
|
|
|
|
func x25519(dst *[32]byte, scalar, point []byte) ([]byte, error) {
|
|
curve := ecdh.X25519()
|
|
pub, err := curve.NewPublicKey(point)
|
|
if err != nil {
|
|
return nil, err
|
|
}
|
|
priv, err := curve.NewPrivateKey(scalar)
|
|
if err != nil {
|
|
return nil, err
|
|
}
|
|
out, err := priv.ECDH(pub)
|
|
if err != nil {
|
|
return nil, err
|
|
}
|
|
copy(dst[:], out)
|
|
return dst[:], nil
|
|
}
|