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tailscale/types/key/key.go

125 lines
3.2 KiB
Go

// Copyright (c) 2020 Tailscale Inc & 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 key defines some types related to curve25519 keys.
package key
import (
crand "crypto/rand"
"encoding/base64"
"errors"
"fmt"
"io"
"go4.org/mem"
"golang.org/x/crypto/curve25519"
)
// Private represents a curve25519 private key.
type Private [32]byte
// Private reports whether p is the zero value.
func (p Private) IsZero() bool { return p == Private{} }
// NewPrivate returns a new private key.
func NewPrivate() Private {
var p Private
if _, err := io.ReadFull(crand.Reader, p[:]); err != nil {
panic(err)
}
p[0] &= 248
p[31] = (p[31] & 127) | 64
return p
}
// B32 returns k as the *[32]byte type that's used by the
// golang.org/x/crypto packages. This allocates; it might
// not be appropriate for performance-sensitive paths.
func (k Private) B32() *[32]byte { return (*[32]byte)(&k) }
// Public represents a curve25519 public key.
type Public [32]byte
// Public reports whether p is the zero value.
func (p Public) IsZero() bool { return p == Public{} }
// ShortString returns the Tailscale conventional debug representation
// of a public key: the first five base64 digits of the key, in square
// brackets.
func (p Public) ShortString() string {
return "[" + base64.StdEncoding.EncodeToString(p[:])[:5] + "]"
}
func (p Public) MarshalText() ([]byte, error) {
buf := make([]byte, base64.StdEncoding.EncodedLen(len(p)))
base64.StdEncoding.Encode(buf, p[:])
return buf, nil
}
func (p *Public) UnmarshalText(txt []byte) error {
if *p != (Public{}) {
return errors.New("refusing to unmarshal into non-zero key.Public")
}
n, err := base64.StdEncoding.Decode(p[:], txt)
if err != nil {
return err
}
if n != 32 {
return fmt.Errorf("short decode of %d; want 32", n)
}
return nil
}
// B32 returns k as the *[32]byte type that's used by the
// golang.org/x/crypto packages. This allocates; it might
// not be appropriate for performance-sensitive paths.
func (k Public) B32() *[32]byte { return (*[32]byte)(&k) }
func (k Private) Public() Public {
var pub [32]byte
curve25519.ScalarBaseMult(&pub, (*[32]byte)(&k))
return Public(pub)
}
func (k Private) SharedSecret(pub Public) (ss [32]byte) {
apk := (*[32]byte)(&pub)
ask := (*[32]byte)(&k)
//lint:ignore SA1019 Code copied from wireguard-go, we aim for
//minimal changes from it.
curve25519.ScalarMult(&ss, ask, apk)
return ss
}
// NewPublicFromHexMem parses a public key in its hex form, given in m.
// The provided m must be exactly 64 bytes in length.
func NewPublicFromHexMem(m mem.RO) (Public, error) {
if m.Len() != 64 {
return Public{}, errors.New("invalid length")
}
var p Public
for i := range p {
a, ok1 := fromHexChar(m.At(i*2 + 0))
b, ok2 := fromHexChar(m.At(i*2 + 1))
if !ok1 || !ok2 {
return Public{}, errors.New("invalid hex character")
}
p[i] = (a << 4) | b
}
return p, nil
}
// fromHexChar converts a hex character into its value and a success flag.
func fromHexChar(c byte) (byte, bool) {
switch {
case '0' <= c && c <= '9':
return c - '0', true
case 'a' <= c && c <= 'f':
return c - 'a' + 10, true
case 'A' <= c && c <= 'F':
return c - 'A' + 10, true
}
return 0, false
}