mirror of
https://github.com/go-gitea/gitea
synced 2024-11-09 11:31:34 +01:00
95 lines
3.1 KiB
Go
95 lines
3.1 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.
|
|
package curve25519 // import "golang.org/x/crypto/curve25519"
|
|
|
|
import (
|
|
"crypto/subtle"
|
|
"fmt"
|
|
)
|
|
|
|
// 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) {
|
|
scalarMult(dst, scalar, point)
|
|
}
|
|
|
|
// 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) {
|
|
ScalarMult(dst, scalar, &basePoint)
|
|
}
|
|
|
|
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, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}
|
|
|
|
func init() { Basepoint = basePoint[:] }
|
|
|
|
func checkBasepoint() {
|
|
if subtle.ConstantTimeCompare(Basepoint, []byte{
|
|
0x09, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
|
|
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
|
|
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
|
|
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
|
|
}) != 1 {
|
|
panic("curve25519: global Basepoint value was modified")
|
|
}
|
|
}
|
|
|
|
// 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) {
|
|
var in [32]byte
|
|
if l := len(scalar); l != 32 {
|
|
return nil, fmt.Errorf("bad scalar length: %d, expected %d", l, 32)
|
|
}
|
|
if l := len(point); l != 32 {
|
|
return nil, fmt.Errorf("bad point length: %d, expected %d", l, 32)
|
|
}
|
|
copy(in[:], scalar)
|
|
if &point[0] == &Basepoint[0] {
|
|
checkBasepoint()
|
|
ScalarBaseMult(dst, &in)
|
|
} else {
|
|
var base, zero [32]byte
|
|
copy(base[:], point)
|
|
ScalarMult(dst, &in, &base)
|
|
if subtle.ConstantTimeCompare(dst[:], zero[:]) == 1 {
|
|
return nil, fmt.Errorf("bad input point: low order point")
|
|
}
|
|
}
|
|
return dst[:], nil
|
|
}
|