mirror of
https://github.com/tailscale/tailscale.git
synced 2024-11-25 19:15:34 +00:00
118 lines
3.6 KiB
Go
118 lines
3.6 KiB
Go
// Copyright (c) Tailscale Inc & AUTHORS
|
|
// SPDX-License-Identifier: BSD-3-Clause
|
|
|
|
package key
|
|
|
|
import (
|
|
crand "crypto/rand"
|
|
"encoding/base64"
|
|
"encoding/hex"
|
|
"errors"
|
|
"fmt"
|
|
"io"
|
|
"slices"
|
|
|
|
"go4.org/mem"
|
|
)
|
|
|
|
// rand fills b with cryptographically strong random bytes. Panics if
|
|
// no random bytes are available.
|
|
func rand(b []byte) {
|
|
if _, err := io.ReadFull(crand.Reader, b[:]); err != nil {
|
|
panic(fmt.Sprintf("unable to read random bytes from OS: %v", err))
|
|
}
|
|
}
|
|
|
|
// clamp25519 clamps b, which must be a 32-byte Curve25519 private
|
|
// key, to a safe value.
|
|
//
|
|
// The clamping effectively constrains the key to a number between
|
|
// 2^251 and 2^252-1, which is then multiplied by 8 (the cofactor of
|
|
// Curve25519). This produces a value that doesn't have any unsafe
|
|
// properties when doing operations like ScalarMult.
|
|
//
|
|
// See
|
|
// https://web.archive.org/web/20210228105330/https://neilmadden.blog/2020/05/28/whats-the-curve25519-clamping-all-about/
|
|
// for a more in-depth explanation of the constraints that led to this
|
|
// clamping requirement.
|
|
//
|
|
// PLEASE NOTE that not all Curve25519 values require clamping. When
|
|
// implementing a new key type that uses Curve25519, you must evaluate
|
|
// whether that particular key's use requires clamping. Here are some
|
|
// existing uses and whether you should clamp private keys at
|
|
// creation.
|
|
//
|
|
// - NaCl box: yes, clamp at creation.
|
|
// - WireGuard (userspace uapi or kernel): no, do not clamp.
|
|
// - Noise protocols: no, do not clamp.
|
|
func clamp25519Private(b []byte) {
|
|
b[0] &= 248
|
|
b[31] = (b[31] & 127) | 64
|
|
}
|
|
|
|
func appendHexKey(dst []byte, prefix string, key []byte) []byte {
|
|
dst = slices.Grow(dst, len(prefix)+hex.EncodedLen(len(key)))
|
|
dst = append(dst, prefix...)
|
|
dst = hex.AppendEncode(dst, key)
|
|
return dst
|
|
}
|
|
|
|
// parseHex decodes a key string of the form "<prefix><hex string>"
|
|
// into out. The prefix must match, and the decoded base64 must fit
|
|
// exactly into out.
|
|
//
|
|
// Note the errors in this function deliberately do not echo the
|
|
// contents of in, because it might be a private key or part of a
|
|
// private key.
|
|
func parseHex(out []byte, in, prefix mem.RO) error {
|
|
if !mem.HasPrefix(in, prefix) {
|
|
return fmt.Errorf("key hex string doesn't have expected type prefix %s", prefix.StringCopy())
|
|
}
|
|
in = in.SliceFrom(prefix.Len())
|
|
if want := len(out) * 2; in.Len() != want {
|
|
return fmt.Errorf("key hex has the wrong size, got %d want %d", in.Len(), want)
|
|
}
|
|
for i := range out {
|
|
a, ok1 := fromHexChar(in.At(i*2 + 0))
|
|
b, ok2 := fromHexChar(in.At(i*2 + 1))
|
|
if !ok1 || !ok2 {
|
|
return errors.New("invalid hex character in key")
|
|
}
|
|
out[i] = (a << 4) | b
|
|
}
|
|
return 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
|
|
}
|
|
|
|
// debug32 returns the Tailscale conventional debug representation of
|
|
// a key: the first five base64 digits of the key, in square brackets.
|
|
func debug32(k [32]byte) string {
|
|
if k == [32]byte{} {
|
|
return ""
|
|
}
|
|
|
|
// The goal here is to generate "[" + base64.StdEncoding.EncodeToString(k[:])[:5] + "]".
|
|
// Since we only care about the first 5 characters, it suffices to encode the first 4 bytes of k.
|
|
// Encoding those 4 bytes requires 8 bytes.
|
|
// Make dst have size 9, to fit the leading '[' plus those 8 bytes.
|
|
// We slice the unused ones away at the end.
|
|
dst := make([]byte, 9)
|
|
dst[0] = '['
|
|
base64.StdEncoding.Encode(dst[1:], k[:4])
|
|
dst[6] = ']'
|
|
return string(dst[:7])
|
|
}
|