mirror of
https://github.com/tailscale/tailscale.git
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254 lines
6.9 KiB
Go
254 lines
6.9 KiB
Go
// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Package wgkey contains types and helpers for WireGuard keys.
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// It is very similar to package tailscale.com/types/key,
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// which is also used for curve25519 keys.
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// These keys are used for WireGuard clients;
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// those keys are used in other curve25519 clients.
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package wgkey
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import (
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"crypto/rand"
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"crypto/subtle"
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"encoding/base64"
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"encoding/hex"
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"errors"
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"fmt"
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"strings"
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"golang.org/x/crypto/chacha20poly1305"
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"golang.org/x/crypto/curve25519"
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)
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// Size is the number of bytes in a curve25519 key.
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const Size = 32
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// A Key is a curve25519 key.
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// It is used by WireGuard to represent public and preshared keys.
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type Key [Size]byte
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// NewPreshared generates a new random Key.
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func NewPreshared() (*Key, error) {
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var k [Size]byte
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_, err := rand.Read(k[:])
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if err != nil {
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return nil, err
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}
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return (*Key)(&k), nil
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}
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func Parse(b64 string) (*Key, error) { return parseBase64(base64.StdEncoding, b64) }
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func ParseHex(s string) (Key, error) {
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b, err := hex.DecodeString(s)
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if err != nil {
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return Key{}, fmt.Errorf("invalid hex key (%q): %w", s, err)
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}
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if len(b) != Size {
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return Key{}, fmt.Errorf("invalid hex key (%q): length=%d, want %d", s, len(b), Size)
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}
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var key Key
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copy(key[:], b)
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return key, nil
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}
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func ParsePrivateHex(v string) (Private, error) {
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k, err := ParseHex(v)
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if err != nil {
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return Private{}, err
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}
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pk := Private(k)
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if pk.IsZero() {
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// Do not clamp a zero key, pass the zero through
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// (much like NaN propagation) so that IsZero reports
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// a useful result.
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return pk, nil
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}
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pk.clamp()
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return pk, nil
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}
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func (k Key) Base64() string { return base64.StdEncoding.EncodeToString(k[:]) }
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func (k Key) String() string { return k.ShortString() }
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func (k Key) HexString() string { return hex.EncodeToString(k[:]) }
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func (k Key) Equal(k2 Key) bool { return subtle.ConstantTimeCompare(k[:], k2[:]) == 1 }
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func (k Key) AppendTo(b []byte) []byte { return appendKey(b, "", k) }
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func (k *Key) ShortString() string {
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// The goal here is to generate "[" + base64.StdEncoding.EncodeToString(k[:])[:5] + "]".
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// Since we only care about the first 5 characters, it suffices to encode the first 4 bytes of k.
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// Encoding those 4 bytes requires 8 bytes.
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// Make dst have size 9, to fit the leading '[' plus those 8 bytes.
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// We slice the unused ones away at the end.
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dst := make([]byte, 9)
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dst[0] = '['
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base64.StdEncoding.Encode(dst[1:], k[:4])
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dst[6] = ']'
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return string(dst[:7])
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}
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func (k *Key) IsZero() bool {
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if k == nil {
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return true
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}
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var zeros Key
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return subtle.ConstantTimeCompare(zeros[:], k[:]) == 1
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}
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func (k Key) MarshalJSON() ([]byte, error) {
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buf := make([]byte, 2+len(k)*2)
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buf[0] = '"'
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hex.Encode(buf[1:], k[:])
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buf[len(buf)-1] = '"'
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return buf, nil
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}
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func (k *Key) UnmarshalJSON(b []byte) error {
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if k == nil {
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return errors.New("wgkey.Key: UnmarshalJSON on nil pointer")
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}
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if len(b) < 3 || b[0] != '"' || b[len(b)-1] != '"' {
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return errors.New("wgkey.Key: UnmarshalJSON not given a string")
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}
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b = b[1 : len(b)-1]
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if len(b) != 2*Size {
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return fmt.Errorf("wgkey.Key: UnmarshalJSON input wrong size: %d", len(b))
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}
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hex.Decode(k[:], b)
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return nil
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}
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func (a *Key) LessThan(b *Key) bool {
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for i := range a {
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if a[i] < b[i] {
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return true
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} else if a[i] > b[i] {
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return false
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}
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}
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return false
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}
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// A Private is a curve25519 key.
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// It is used by WireGuard to represent private keys.
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type Private [Size]byte
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// NewPrivate generates a new curve25519 secret key.
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// It conforms to the format described on https://cr.yp.to/ecdh.html.
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//
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// TODO: make this look more like types/key, key generation should not
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// return an error.
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func NewPrivate() (Private, error) {
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k, err := NewPreshared()
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if err != nil {
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return Private{}, err
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}
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k[0] &= 248
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k[31] = (k[31] & 127) | 64
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return (Private)(*k), nil
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}
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func ParsePrivate(b64 string) (*Private, error) {
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k, err := parseBase64(base64.StdEncoding, b64)
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return (*Private)(k), err
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}
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func (k *Private) String() string { return base64.StdEncoding.EncodeToString(k[:]) }
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func (k *Private) HexString() string { return hex.EncodeToString(k[:]) }
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func (k *Private) Equal(k2 Private) bool { return subtle.ConstantTimeCompare(k[:], k2[:]) == 1 }
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func (k *Private) IsZero() bool {
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pk := Key(*k)
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return pk.IsZero()
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}
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func (k *Private) clamp() {
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k[0] &= 248
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k[31] = (k[31] & 127) | 64
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}
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// Public computes the public key matching this curve25519 secret key.
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func (k *Private) Public() Key {
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pk := Key(*k)
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if pk.IsZero() {
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panic("Tried to generate emptyPrivate.Public()")
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}
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var p [Size]byte
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curve25519.ScalarBaseMult(&p, (*[Size]byte)(k))
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return (Key)(p)
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}
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func appendKey(base []byte, prefix string, k [32]byte) []byte {
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ret := append(base, make([]byte, len(prefix)+64)...)
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buf := ret[len(base):]
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copy(buf, prefix)
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hex.Encode(buf[len(prefix):], k[:])
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return ret
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}
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func (k Private) MarshalText() ([]byte, error) { return appendKey(nil, "privkey:", k), nil }
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func (k Private) AppendTo(b []byte) []byte { return appendKey(b, "privkey:", k) }
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func (k *Private) UnmarshalText(b []byte) error {
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s := string(b)
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if !strings.HasPrefix(s, `privkey:`) {
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return errors.New("wgkey.Private: UnmarshalText not given a private-key string")
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}
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s = strings.TrimPrefix(s, `privkey:`)
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key, err := ParseHex(s)
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if err != nil {
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return fmt.Errorf("wgkey.Private: UnmarshalText: %v", err)
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}
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copy(k[:], key[:])
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return nil
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}
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func parseBase64(enc *base64.Encoding, s string) (*Key, error) {
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k, err := enc.DecodeString(s)
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if err != nil {
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return nil, fmt.Errorf("invalid key (%q): %w", s, err)
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}
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if len(k) != Size {
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return nil, fmt.Errorf("invalid key (%q): length=%d, want %d", s, len(k), Size)
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}
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var key Key
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copy(key[:], k)
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return &key, nil
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}
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func ParseSymmetric(b64 string) (Symmetric, error) {
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k, err := parseBase64(base64.StdEncoding, b64)
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if err != nil {
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return Symmetric{}, err
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}
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return Symmetric(*k), nil
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}
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func ParseSymmetricHex(s string) (Symmetric, error) {
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b, err := hex.DecodeString(s)
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if err != nil {
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return Symmetric{}, fmt.Errorf("invalid symmetric hex key (%q): %w", s, err)
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}
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if len(b) != chacha20poly1305.KeySize {
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return Symmetric{}, fmt.Errorf("invalid symmetric hex key length (%q): length=%d, want %d", s, len(b), chacha20poly1305.KeySize)
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}
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var key Symmetric
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copy(key[:], b)
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return key, nil
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}
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// Symmetric is a chacha20poly1305 key.
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// It is used by WireGuard to represent pre-shared symmetric keys.
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type Symmetric [chacha20poly1305.KeySize]byte
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func (k Symmetric) Base64() string { return base64.StdEncoding.EncodeToString(k[:]) }
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func (k Symmetric) String() string { return "sym:" + k.Base64()[:8] }
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func (k Symmetric) HexString() string { return hex.EncodeToString(k[:]) }
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func (k Symmetric) IsZero() bool { return k.Equal(Symmetric{}) }
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func (k Symmetric) Equal(k2 Symmetric) bool {
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return subtle.ConstantTimeCompare(k[:], k2[:]) == 1
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}
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