mirror of https://github.com/tailscale/tailscale/
types/key: add MachinePrivate and MachinePublic.
Plumb throughout the codebase as a replacement for the mixed use of tailcfg.MachineKey and wgkey.Private/Public. Signed-off-by: David Anderson <danderson@tailscale.com>pull/2792/head
David Anderson
3 years ago
committed by
Dave Anderson
parent
4ce091cbd8
commit
4fdb88efe1
@ -0,0 +1,173 @@
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// Copyright (c) 2021 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 key
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import (
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"crypto/subtle"
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"encoding/hex"
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"go4.org/mem"
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"golang.org/x/crypto/curve25519"
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"golang.org/x/crypto/nacl/box"
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"tailscale.com/types/structs"
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)
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const (
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// machinePrivateHexPrefix is the prefix used to identify a
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// hex-encoded machine private key.
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//
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// This prefix name is a little unfortunate, in that it comes from
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// WireGuard's own key types. Unfortunately we're stuck with it for
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// machine keys, because we serialize them to disk with this prefix.
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machinePrivateHexPrefix = "privkey:"
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// machinePublicHexPrefix is the prefix used to identify a
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// hex-encoded machine public key.
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//
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// This prefix is used in the control protocol, so cannot be
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// changed.
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machinePublicHexPrefix = "mkey:"
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)
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// MachinePrivate is a machine key, used for communication with the
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// Tailscale coordination server.
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type MachinePrivate struct {
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_ structs.Incomparable // == isn't constant-time
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k [32]byte
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}
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// NewMachine creates and returns a new machine private key.
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func NewMachine() MachinePrivate {
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var ret MachinePrivate
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rand(ret.k[:])
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clamp25519Private(ret.k[:])
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return ret
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}
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// IsZero reports whether k is the zero value.
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func (k MachinePrivate) IsZero() bool {
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return k.Equal(MachinePrivate{})
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}
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// Equal reports whether k and other are the same key.
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func (k MachinePrivate) Equal(other MachinePrivate) bool {
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return subtle.ConstantTimeCompare(k.k[:], other.k[:]) == 1
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}
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// Public returns the MachinePublic for k.
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// Panics if MachinePublic is zero.
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func (k MachinePrivate) Public() MachinePublic {
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if k.IsZero() {
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panic("can't take the public key of a zero MachinePrivate")
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}
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var ret MachinePublic
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curve25519.ScalarBaseMult(&ret.k, &k.k)
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return ret
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}
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// MarshalText implements encoding.TextMarshaler.
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func (k MachinePrivate) MarshalText() ([]byte, error) {
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return toHex(k.k[:], machinePrivateHexPrefix), nil
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}
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// MarshalText implements encoding.TextUnmarshaler.
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func (k *MachinePrivate) UnmarshalText(b []byte) error {
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return parseHex(k.k[:], mem.B(b), mem.S(machinePrivateHexPrefix))
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}
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// SealTo wraps cleartext into a NaCl box (see
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// golang.org/x/crypto/nacl) to p, authenticated from k, using a
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// random nonce.
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//
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// The returned ciphertext is a 24-byte nonce concatenated with the
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// box value.
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func (k MachinePrivate) SealTo(p MachinePublic, cleartext []byte) (ciphertext []byte) {
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if k.IsZero() || p.IsZero() {
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panic("can't seal with zero keys")
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}
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var nonce [24]byte
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rand(nonce[:])
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return box.Seal(nonce[:], cleartext, &nonce, &p.k, &k.k)
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}
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// OpenFrom opens the NaCl box ciphertext, which must be a value
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// created by SealTo, and returns the inner cleartext if ciphertext is
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// a valid box from p to k.
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func (k MachinePrivate) OpenFrom(p MachinePublic, ciphertext []byte) (cleartext []byte, ok bool) {
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if k.IsZero() || p.IsZero() {
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panic("can't open with zero keys")
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}
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if len(ciphertext) < 24 {
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return nil, false
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}
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var nonce [24]byte
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copy(nonce[:], ciphertext)
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return box.Open(nil, ciphertext[len(nonce):], &nonce, &p.k, &k.k)
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}
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// MachinePublic is the public portion of a a MachinePrivate.
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type MachinePublic struct {
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k [32]byte
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}
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// ParseMachinePublicUntyped parses an untyped 64-character hex value
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// as a MachinePublic.
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//
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// Deprecated: this function is risky to use, because it cannot verify
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// that the hex string was intended to be a MachinePublic. This can
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// lead to accidentally decoding one type of key as another. For new
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// uses that don't require backwards compatibility with the untyped
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// string format, please use MarshalText/UnmarshalText.
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func ParseMachinePublicUntyped(raw mem.RO) (MachinePublic, error) {
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var ret MachinePublic
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if err := parseHex(ret.k[:], raw, mem.B(nil)); err != nil {
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return MachinePublic{}, err
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}
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return ret, nil
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}
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// IsZero reports whether k is the zero value.
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func (k MachinePublic) IsZero() bool {
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return k == MachinePublic{}
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}
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// ShortString returns the Tailscale conventional debug representation
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// of a public key: the first five base64 digits of the key, in square
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// brackets.
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func (k MachinePublic) ShortString() string {
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return debug32(k.k)
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}
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// UntypedHexString returns k, encoded as an untyped 64-character hex
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// string.
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//
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// Deprecated: this function is risky to use, because it produces
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// serialized values that do not identify themselves as a
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// MachinePublic, allowing other code to potentially parse it back in
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// as the wrong key type. For new uses that don't require backwards
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// compatibility with the untyped string format, please use
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// MarshalText/UnmarshalText.
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func (k MachinePublic) UntypedHexString() string {
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return hex.EncodeToString(k.k[:])
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}
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// String returns the output of MarshalText as a string.
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func (k MachinePublic) String() string {
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bs, err := k.MarshalText()
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if err != nil {
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panic(err)
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}
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return string(bs)
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}
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// MarshalText implements encoding.TextMarshaler.
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func (k MachinePublic) MarshalText() ([]byte, error) {
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return toHex(k.k[:], machinePublicHexPrefix), nil
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}
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// MarshalText implements encoding.TextUnmarshaler.
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func (k *MachinePublic) UnmarshalText(b []byte) error {
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return parseHex(k.k[:], mem.B(b), mem.S(machinePublicHexPrefix))
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}
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@ -0,0 +1,92 @@
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// Copyright (c) 2021 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 key
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import (
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"bytes"
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"encoding/json"
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"strings"
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"testing"
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)
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func TestMachineKey(t *testing.T) {
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k := NewMachine()
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if k.IsZero() {
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t.Fatal("MachinePrivate should not be zero")
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}
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p := k.Public()
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if p.IsZero() {
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t.Fatal("MachinePublic should not be zero")
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}
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bs, err := p.MarshalText()
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if err != nil {
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t.Fatal(err)
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}
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if full, got := string(bs), ":"+p.UntypedHexString(); !strings.HasSuffix(full, got) {
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t.Fatalf("MachinePublic.UntypedHexString is not a suffix of the typed serialization, got %q want suffix of %q", got, full)
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}
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z := MachinePublic{}
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if !z.IsZero() {
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t.Fatal("IsZero(MachinePublic{}) is false")
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}
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if s := z.ShortString(); s != "" {
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t.Fatalf("MachinePublic{}.ShortString() is %q, want \"\"", s)
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}
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}
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func TestMachineSerialization(t *testing.T) {
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serialized := `{
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"Priv": "privkey:40ab1b58e9076c7a4d9d07291f5edf9d1aa017eb949624ba683317f48a640369",
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"Pub":"mkey:50d20b455ecf12bc453f83c2cfdb2a24925d06cf2598dcaa54e91af82ce9f765"
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}`
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// Carefully check that the expected serialized data decodes and
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// reencodes to the expected keys. These types are serialized to
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// disk all over the place and need to be stable.
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priv := MachinePrivate{
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k: [32]uint8{
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0x40, 0xab, 0x1b, 0x58, 0xe9, 0x7, 0x6c, 0x7a, 0x4d, 0x9d, 0x7,
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0x29, 0x1f, 0x5e, 0xdf, 0x9d, 0x1a, 0xa0, 0x17, 0xeb, 0x94,
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0x96, 0x24, 0xba, 0x68, 0x33, 0x17, 0xf4, 0x8a, 0x64, 0x3, 0x69,
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},
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}
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pub := MachinePublic{
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k: [32]uint8{
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0x50, 0xd2, 0xb, 0x45, 0x5e, 0xcf, 0x12, 0xbc, 0x45, 0x3f, 0x83,
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0xc2, 0xcf, 0xdb, 0x2a, 0x24, 0x92, 0x5d, 0x6, 0xcf, 0x25, 0x98,
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0xdc, 0xaa, 0x54, 0xe9, 0x1a, 0xf8, 0x2c, 0xe9, 0xf7, 0x65,
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},
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}
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type keypair struct {
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Priv MachinePrivate
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Pub MachinePublic
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}
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var a keypair
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if err := json.Unmarshal([]byte(serialized), &a); err != nil {
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t.Fatal(err)
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}
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if !a.Priv.Equal(priv) {
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t.Errorf("wrong deserialization of private key, got %#v want %#v", a.Priv, priv)
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}
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if a.Pub != pub {
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t.Errorf("wrong deserialization of public key, got %#v want %#v", a.Pub, pub)
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}
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bs, err := json.MarshalIndent(a, "", " ")
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if err != nil {
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t.Fatal(err)
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}
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var b bytes.Buffer
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json.Indent(&b, []byte(serialized), "", " ")
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if got, want := string(bs), b.String(); got != want {
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t.Error("json serialization doesn't roundtrip")
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}
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}
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@ -0,0 +1,111 @@
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// Copyright (c) 2021 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 key
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import (
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crand "crypto/rand"
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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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"io"
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"go4.org/mem"
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)
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// rand fills b with cryptographically strong random bytes. Panics if
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// no random bytes are available.
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func rand(b []byte) {
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if _, err := io.ReadFull(crand.Reader, b[:]); err != nil {
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panic(fmt.Sprintf("unable to read random bytes from OS: %v", err))
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}
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}
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// clamp25519 clamps b, which must be a 32-byte Curve25519 private
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// key, to a safe value.
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//
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// The clamping effectively constrains the key to a number between
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// 2^251 and 2^252-1, which is then multiplied by 8 (the cofactor of
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// Curve25519). This produces a value that doesn't have any unsafe
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// properties when doing operations like ScalarMult.
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//
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// See
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// https://web.archive.org/web/20210228105330/https://neilmadden.blog/2020/05/28/whats-the-curve25519-clamping-all-about/
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// for a more in-depth explanation of the constraints that led to this
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// clamping requirement.
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//
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// PLEASE NOTE that not all Curve25519 values require clamping. When
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// implementing a new key type that uses Curve25519, you must evaluate
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// whether that particular key's use requires clamping. Here are some
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// existing uses and whether you should clamp private keys at
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// creation.
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//
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// - NaCl box: yes, clamp at creation.
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// - WireGuard (userspace uapi or kernel): no, do not clamp.
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// - Noise protocols: no, do not clamp.
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func clamp25519Private(b []byte) {
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b[0] &= 248
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b[31] = (b[31] & 127) | 64
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}
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func toHex(k []byte, prefix string) []byte {
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ret := make([]byte, len(prefix)+len(k)*2)
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copy(ret, prefix)
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hex.Encode(ret[len(prefix):], k)
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return ret
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}
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// parseHex decodes a key string of the form "<prefix><hex string>"
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// into out. The prefix must match, and the decoded base64 must fit
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// exactly into out.
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//
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// Note the errors in this function deliberately do not echo the
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// contents of in, because it might be a private key or part of a
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// private key.
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func parseHex(out []byte, in, prefix mem.RO) error {
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if !mem.HasPrefix(in, prefix) {
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return fmt.Errorf("key hex string doesn't have expected type prefix %s", prefix.StringCopy())
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}
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in = in.SliceFrom(prefix.Len())
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if want := len(out) * 2; in.Len() != want {
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return fmt.Errorf("key hex has the wrong size, got %d want %d", in.Len(), want)
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}
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for i := range out {
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a, ok1 := fromHexChar(in.At(i*2 + 0))
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b, ok2 := fromHexChar(in.At(i*2 + 1))
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if !ok1 || !ok2 {
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return errors.New("invalid hex character in key")
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}
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out[i] = (a << 4) | b
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}
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return nil
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}
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// fromHexChar converts a hex character into its value and a success flag.
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func fromHexChar(c byte) (byte, bool) {
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switch {
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case '0' <= c && c <= '9':
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return c - '0', true
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case 'a' <= c && c <= 'f':
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return c - 'a' + 10, true
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case 'A' <= c && c <= 'F':
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return c - 'A' + 10, true
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}
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return 0, false
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}
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// debug32 returns the Tailscale conventional debug representation of
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// a key: the first five base64 digits of the key, in square brackets.
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func debug32(k [32]byte) string {
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if k == [32]byte{} {
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return ""
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}
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var b [45]byte // 32 bytes expands to 44 bytes in base64, plus 1 for the leading '['
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base64.StdEncoding.Encode(b[1:], k[:])
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b[0] = '['
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b[6] = ']'
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return string(b[:7])
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}
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@ -0,0 +1,38 @@
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// Copyright (c) 2021 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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|
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package key
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import (
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"bytes"
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"testing"
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)
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func TestRand(t *testing.T) {
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var bs [32]byte
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rand(bs[:])
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if bs == [32]byte{} {
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t.Fatal("rand didn't provide randomness")
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}
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var bs2 [32]byte
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rand(bs2[:])
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if bytes.Equal(bs[:], bs2[:]) {
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t.Fatal("rand returned the same data twice")
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}
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}
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func TestClamp25519Private(t *testing.T) {
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for i := 0; i < 100; i++ {
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var k [32]byte
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rand(k[:])
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clamp25519Private(k[:])
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if k[0]&0b111 != 0 {
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t.Fatalf("Bogus clamping in first byte: %#08b", k[0])
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return
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}
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if k[31]>>6 != 1 {
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t.Fatalf("Bogus clamping in last byte: %#08b", k[0])
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}
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}
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}
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Loading…
Reference in New Issue