122 lines
3.2 KiB
Go
122 lines
3.2 KiB
Go
|
// Copyright (c) 2022 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 tka
|
||
|
|
||
|
import (
|
||
|
"crypto/ed25519"
|
||
|
"errors"
|
||
|
"fmt"
|
||
|
|
||
|
"github.com/hdevalence/ed25519consensus"
|
||
|
)
|
||
|
|
||
|
// KeyKind describes the different varieties of a Key.
|
||
|
type KeyKind uint8
|
||
|
|
||
|
// Valid KeyKind values.
|
||
|
const (
|
||
|
KeyInvalid KeyKind = iota
|
||
|
Key25519
|
||
|
)
|
||
|
|
||
|
func (k KeyKind) String() string {
|
||
|
switch k {
|
||
|
case KeyInvalid:
|
||
|
return "invalid"
|
||
|
case Key25519:
|
||
|
return "25519"
|
||
|
default:
|
||
|
return fmt.Sprintf("Key?<%d>", int(k))
|
||
|
}
|
||
|
}
|
||
|
|
||
|
// Key describes the public components of a key known to network-lock.
|
||
|
type Key struct {
|
||
|
Kind KeyKind `cbor:"1,keyasint"`
|
||
|
|
||
|
// Votes describes the weight applied to signatures using this key.
|
||
|
// Weighting is used to deterministically resolve branches in the AUM
|
||
|
// chain (i.e. forks, where two AUMs exist with the same parent).
|
||
|
Votes uint `cbor:"2,keyasint"`
|
||
|
|
||
|
// Public encodes the public key of the key. For 25519 keys,
|
||
|
// this is simply the point on the curve representing the public
|
||
|
// key.
|
||
|
Public []byte `cbor:"3,keyasint"`
|
||
|
|
||
|
// Meta describes arbitrary metadata about the key. This could be
|
||
|
// used to store the name of the key, for instance.
|
||
|
Meta map[string]string `cbor:"12,keyasint,omitempty"`
|
||
|
}
|
||
|
|
||
|
func (k Key) ID() KeyID {
|
||
|
switch k.Kind {
|
||
|
// Because 25519 public keys are so short, we just use the 32-byte
|
||
|
// public as their 'key ID'.
|
||
|
case Key25519:
|
||
|
return KeyID(k.Public)
|
||
|
default:
|
||
|
panic("unsupported key kind")
|
||
|
}
|
||
|
}
|
||
|
|
||
|
const maxMetaBytes = 512
|
||
|
|
||
|
func (k Key) StaticValidate() error {
|
||
|
if k.Votes > 4096 {
|
||
|
return fmt.Errorf("excessive key weight: %d > 4096", k.Votes)
|
||
|
}
|
||
|
|
||
|
// We have an arbitrary upper limit on the amount
|
||
|
// of metadata that can be associated with a key, so
|
||
|
// people don't start using it as a key-value store and
|
||
|
// causing pathological cases due to the number + size of
|
||
|
// AUMs.
|
||
|
var metaBytes uint
|
||
|
for k, v := range k.Meta {
|
||
|
metaBytes += uint(len(k) + len(v))
|
||
|
}
|
||
|
if metaBytes > maxMetaBytes {
|
||
|
return fmt.Errorf("key metadata too big (%d > %d)", metaBytes, maxMetaBytes)
|
||
|
}
|
||
|
|
||
|
switch k.Kind {
|
||
|
case Key25519:
|
||
|
default:
|
||
|
return fmt.Errorf("unrecognized key kind: %v", k.Kind)
|
||
|
}
|
||
|
return nil
|
||
|
}
|
||
|
|
||
|
// KeyID references a verification key stored in the key authority.
|
||
|
//
|
||
|
// For 25519 keys: The 32-byte public key.
|
||
|
type KeyID []byte
|
||
|
|
||
|
// Signature describes a signature over an AUM, which can be verified
|
||
|
// using the key referenced by KeyID.
|
||
|
type Signature struct {
|
||
|
KeyID KeyID `cbor:"1,keyasint"`
|
||
|
Signature []byte `cbor:"2,keyasint"`
|
||
|
}
|
||
|
|
||
|
// Verify returns a nil error if the signature is valid over the
|
||
|
// provided AUM BLAKE2s digest, using the given key.
|
||
|
func (s *Signature) Verify(aumDigest AUMSigHash, key Key) error {
|
||
|
// NOTE(tom): Even if we can compute the public from the KeyID,
|
||
|
// its possible for the KeyID to be attacker-controlled
|
||
|
// so we should use the public contained in the state machine.
|
||
|
switch key.Kind {
|
||
|
case Key25519:
|
||
|
if ed25519consensus.Verify(ed25519.PublicKey(key.Public), aumDigest[:], s.Signature) {
|
||
|
return nil
|
||
|
}
|
||
|
return errors.New("invalid signature")
|
||
|
|
||
|
default:
|
||
|
return fmt.Errorf("unhandled key type: %v", key.Kind)
|
||
|
}
|
||
|
}
|