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tka: implement AUM and Key types

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This is the first in a series of PRs implementing the internals for the
Tailnet Key Authority. This PR implements the AUM and Key types, which
are used by pretty much everything else. Future PRs:

 - The State type & related machinery
 - The Tailchonk (storage) type & implementation
 - The Authority type and sync implementation

Signed-off-by: Tom DNetto <tom@tailscale.com>
This commit is contained in:
Tom DNetto 2022-07-05 13:20:12 -07:00 committed by Tom
parent e6572a0f08
commit 1cfd96cdc2
7 changed files with 656 additions and 0 deletions
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4
go.mod
View File

@ -69,6 +69,7 @@ require (
require (
4d63.com/gochecknoglobals v0.1.0 // indirect
filippo.io/edwards25519 v1.0.0-rc.1 // indirect
github.com/Antonboom/errname v0.1.5 // indirect
github.com/Antonboom/nilnil v0.1.0 // indirect
github.com/BurntSushi/toml v1.1.0 // indirect
@ -121,6 +122,7 @@ require (
github.com/fatih/color v1.13.0 // indirect
github.com/fatih/structtag v1.2.0 // indirect
github.com/fsnotify/fsnotify v1.5.1 // indirect
github.com/fxamacker/cbor/v2 v2.4.0 // indirect
github.com/fzipp/gocyclo v0.3.1 // indirect
github.com/gliderlabs/ssh v0.3.3 // indirect
github.com/go-critic/go-critic v0.6.1 // indirect
@ -162,6 +164,7 @@ require (
github.com/hashicorp/errwrap v1.1.0 // indirect
github.com/hashicorp/go-multierror v1.1.1 // indirect
github.com/hashicorp/hcl v1.0.0 // indirect
github.com/hdevalence/ed25519consensus v0.0.0-20220222234857-c00d1f31bab3 // indirect
github.com/huandu/xstrings v1.3.2 // indirect
github.com/imdario/mergo v0.3.12 // indirect
github.com/inconshreveable/mousetrap v1.0.0 // indirect
@ -255,6 +258,7 @@ require (
github.com/uudashr/gocognit v1.0.5 // indirect
github.com/vbatts/tar-split v0.11.2 // indirect
github.com/vishvananda/netns v0.0.0-20211101163701-50045581ed74 // indirect
github.com/x448/float16 v0.8.4 // indirect
github.com/xanzy/ssh-agent v0.3.1 // indirect
github.com/yeya24/promlinter v0.1.0 // indirect
go4.org/intern v0.0.0-20211027215823-ae77deb06f29 // indirect

8
go.sum
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@ -52,6 +52,8 @@ cloud.google.com/go/storage v1.8.0/go.mod h1:Wv1Oy7z6Yz3DshWRJFhqM/UCfaWIRTdp0RX
cloud.google.com/go/storage v1.10.0/go.mod h1:FLPqc6j+Ki4BU591ie1oL6qBQGu2Bl/tZ9ullr3+Kg0=
contrib.go.opencensus.io/exporter/stackdriver v0.13.4/go.mod h1:aXENhDJ1Y4lIg4EUaVTwzvYETVNZk10Pu26tevFKLUc=
dmitri.shuralyov.com/gpu/mtl v0.0.0-20190408044501-666a987793e9/go.mod h1:H6x//7gZCb22OMCxBHrMx7a5I7Hp++hsVxbQ4BYO7hU=
filippo.io/edwards25519 v1.0.0-rc.1 h1:m0VOOB23frXZvAOK44usCgLWvtsxIoMCTBGJZlpmGfU=
filippo.io/edwards25519 v1.0.0-rc.1/go.mod h1:N1IkdkCkiLB6tki+MYJoSx2JTY9NUlxZE7eHn5EwJns=
filippo.io/mkcert v1.4.3 h1:axpnmtrZMM8u5Hf4N3UXxboGemMOV+Tn+e+pkHM6E3o=
filippo.io/mkcert v1.4.3/go.mod h1:64ke566uBwAQcdK3vRDABgsgVHqrfORPTw6YytZCTxk=
github.com/Antonboom/errname v0.1.5 h1:IM+A/gz0pDhKmlt5KSNTVAvfLMb+65RxavBXpRtCUEg=
@ -294,6 +296,8 @@ github.com/fsnotify/fsnotify v1.4.9/go.mod h1:znqG4EE+3YCdAaPaxE2ZRY/06pZUdp0tY4
github.com/fsnotify/fsnotify v1.5.1 h1:mZcQUHVQUQWoPXXtuf9yuEXKudkV2sx1E06UadKWpgI=
github.com/fsnotify/fsnotify v1.5.1/go.mod h1:T3375wBYaZdLLcVNkcVbzGHY7f1l/uK5T5Ai1i3InKU=
github.com/fullstorydev/grpcurl v1.6.0/go.mod h1:ZQ+ayqbKMJNhzLmbpCiurTVlaK2M/3nqZCxaQ2Ze/sM=
github.com/fxamacker/cbor/v2 v2.4.0 h1:ri0ArlOR+5XunOP8CRUowT0pSJOwhW098ZCUyskZD88=
github.com/fxamacker/cbor/v2 v2.4.0/go.mod h1:TA1xS00nchWmaBnEIxPSE5oHLuJBAVvqrtAnWBwBCVo=
github.com/fzipp/gocyclo v0.3.1 h1:A9UeX3HJSXTBzvHzhqoYVuE0eAhe+aM8XBCCwsPMZOc=
github.com/fzipp/gocyclo v0.3.1/go.mod h1:DJHO6AUmbdqj2ET4Z9iArSuwWgYDRryYt2wASxc7x3E=
github.com/ghodss/yaml v1.0.0/go.mod h1:4dBDuWmgqj2HViK6kFavaiC9ZROes6MMH2rRYeMEF04=
@ -603,6 +607,8 @@ github.com/hashicorp/memberlist v0.1.3/go.mod h1:ajVTdAv/9Im8oMAAj5G31PhhMCZJV2p
github.com/hashicorp/memberlist v0.2.2/go.mod h1:MS2lj3INKhZjWNqd3N0m3J+Jxf3DAOnAH9VT3Sh9MUE=
github.com/hashicorp/serf v0.8.2/go.mod h1:6hOLApaqBFA1NXqRQAsxw9QxuDEvNxSQRwA/JwenrHc=
github.com/hashicorp/serf v0.9.5/go.mod h1:UWDWwZeL5cuWDJdl0C6wrvrUwEqtQ4ZKBKKENpqIUyk=
github.com/hdevalence/ed25519consensus v0.0.0-20220222234857-c00d1f31bab3 h1:aSVUgRRRtOrZOC1fYmY9gV0e9z/Iu+xNVSASWjsuyGU=
github.com/hdevalence/ed25519consensus v0.0.0-20220222234857-c00d1f31bab3/go.mod h1:5PC6ZNPde8bBqU/ewGZig35+UIZtw9Ytxez8/q5ZyFE=
github.com/hpcloud/tail v1.0.0/go.mod h1:ab1qPbhIpdTxEkNHXyeSf5vhxWSCs/tWer42PpOxQnU=
github.com/huandu/xstrings v1.0.0/go.mod h1:4qWG/gcEcfX4z/mBDHJ++3ReCw9ibxbsNJbcucJdbSo=
github.com/huandu/xstrings v1.2.0/go.mod h1:DvyZB1rfVYsBIigL8HwpZgxHwXozlTgGqn63UyNX5k4=
@ -1172,6 +1178,8 @@ github.com/vishvananda/netlink v1.1.1-0.20211118161826-650dca95af54/go.mod h1:tw
github.com/vishvananda/netns v0.0.0-20200728191858-db3c7e526aae/go.mod h1:DD4vA1DwXk04H54A1oHXtwZmA0grkVMdPxx/VGLCah0=
github.com/vishvananda/netns v0.0.0-20211101163701-50045581ed74 h1:gga7acRE695APm9hlsSMoOoE65U4/TcqNj90mc69Rlg=
github.com/vishvananda/netns v0.0.0-20211101163701-50045581ed74/go.mod h1:DD4vA1DwXk04H54A1oHXtwZmA0grkVMdPxx/VGLCah0=
github.com/x448/float16 v0.8.4 h1:qLwI1I70+NjRFUR3zs1JPUCgaCXSh3SW62uAKT1mSBM=
github.com/x448/float16 v0.8.4/go.mod h1:14CWIYCyZA/cWjXOioeEpHeN/83MdbZDRQHoFcYsOfg=
github.com/xanzy/ssh-agent v0.2.1/go.mod h1:mLlQY/MoOhWBj+gOGMQkOeiEvkx+8pJSI+0Bx9h2kr4=
github.com/xanzy/ssh-agent v0.3.0/go.mod h1:3s9xbODqPuuhK9JV1R321M/FlMZSBvE5aY6eAcqrDh0=
github.com/xanzy/ssh-agent v0.3.1 h1:AmzO1SSWxw73zxFZPRwaMN1MohDw8UyHnmuxyceTEGo=

256
tka/aum.go Normal file
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@ -0,0 +1,256 @@
// 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 (
"bytes"
"crypto/ed25519"
"errors"
"fmt"
"github.com/fxamacker/cbor/v2"
"golang.org/x/crypto/blake2s"
)
// AUMHash represents the BLAKE2s digest of an Authority Update Message (AUM).
type AUMHash [blake2s.Size]byte
// AUMSigHash represents the BLAKE2s digest of an Authority Update
// Message (AUM), sans any signatures.
type AUMSigHash [blake2s.Size]byte
// AUMKind describes valid AUM types.
type AUMKind uint8
// Valid AUM types. Do NOT reorder.
const (
AUMInvalid AUMKind = iota
// An AddKey AUM describes a new key trusted by the TKA.
//
// Only the Key optional field may be set.
AUMAddKey
// A RemoveKey AUM describes hte removal of a key trusted by TKA.
//
// Only the KeyID optional field may be set.
AUMRemoveKey
// A DisableNL AUM describes the disablement of TKA.
//
// Only the DisablementSecret optional field may be set.
AUMDisableNL
// A NoOp AUM carries no information and is used in tests.
AUMNoOp
// A UpdateKey AUM updates the metadata or votes of an existing key.
//
// Only KeyID, along with either/or Meta or Votes optional fields
// may be set.
AUMUpdateKey
// A Checkpoint AUM specifies the full state of the TKA.
//
// Only the State optional field may be set.
AUMCheckpoint
)
func (k AUMKind) String() string {
switch k {
case AUMInvalid:
return "invalid"
case AUMAddKey:
return "add-key"
case AUMRemoveKey:
return "remove-key"
case AUMDisableNL:
return "disable-nl"
case AUMNoOp:
return "no-op"
case AUMCheckpoint:
return "checkpoint"
case AUMUpdateKey:
return "update-key"
default:
return fmt.Sprintf("AUM?<%d>", int(k))
}
}
// AUM describes an Authority Update Message.
//
// The rules for adding new types of AUMs (MessageKind):
// - CBOR key IDs must never be changed.
// - New AUM types must not change semantics that are manipulated by other
// AUM types.
// - The serialization of existing data cannot change (in other words, if
// an existing serialization test in aum_test.go fails, you need to try a
// different approach).
//
// The rules for adding new fields are as follows:
// - Must all be optional.
// - An unset value must not result in serialization overhead. This is
// necessary so the serialization of older AUMs stays the same.
// - New processing semantics of the new fields must be compatible with the
// behavior of old clients (which will ignore the field).
// - No floats!
type AUM struct {
MessageKind AUMKind `cbor:"1,keyasint"`
PrevAUMHash []byte `cbor:"2,keyasint"`
// Key encodes a public key to be added to the key authority.
// This field is used for AddKey AUMs.
Key *Key `cbor:"3,keyasint,omitempty"`
// KeyID references a public key which is part of the key authority.
// This field is used for RemoveKey and UpdateKey AUMs.
KeyID KeyID `cbor:"4,keyasint,omitempty"`
// State describes the full state of the key authority.
// This field is used for Checkpoint AUMs.
// TODO(tom): Use type *State once a future PR brings in that type.
State interface{} `cbor:"5,keyasint,omitempty"`
// DisablementSecret is used to transmit a secret for disabling
// the TKA.
// This field is used for DisableNL AUMs.
DisablementSecret []byte `cbor:"6,keyasint,omitempty"`
// Votes and Meta describe properties of a key in the key authority.
// These fields are used for UpdateKey AUMs.
Votes *uint `cbor:"7,keyasint,omitempty"`
Meta map[string]string `cbor:"8,keyasint,omitempty"`
// Signatures lists the signatures over this AUM.
// CBOR key 23 is the last key which can be encoded as a single byte.
Signatures []Signature `cbor:"23,keyasint,omitempty"`
}
// StaticValidate returns a nil error if the AUM is well-formed.
func (a *AUM) StaticValidate() error {
if a.Key != nil {
if err := a.Key.StaticValidate(); err != nil {
return err
}
}
if a.PrevAUMHash != nil && len(a.PrevAUMHash) == 0 {
return errors.New("absent parent must be represented by a nil slice")
}
for i, sig := range a.Signatures {
if len(sig.KeyID) == 0 || len(sig.Signature) != ed25519.SignatureSize {
return fmt.Errorf("signature %d has missing keyID or malformed signature", i)
}
}
// TODO(tom): Validate State once a future PR brings in that type.
switch a.MessageKind {
case AUMAddKey:
if a.Key == nil {
return errors.New("AddKey AUMs must contain a key")
}
if a.KeyID != nil || a.DisablementSecret != nil || a.State != nil || a.Votes != nil || a.Meta != nil {
return errors.New("AddKey AUMs may only specify a Key")
}
case AUMRemoveKey:
if len(a.KeyID) == 0 {
return errors.New("RemoveKey AUMs must specify a key ID")
}
if a.Key != nil || a.DisablementSecret != nil || a.State != nil || a.Votes != nil || a.Meta != nil {
return errors.New("RemoveKey AUMs may only specify a KeyID")
}
case AUMUpdateKey:
if len(a.KeyID) == 0 {
return errors.New("UpdateKey AUMs must specify a key ID")
}
if a.Meta == nil && a.Votes == nil {
return errors.New("UpdateKey AUMs must contain an update to votes or key metadata")
}
if a.Key != nil || a.DisablementSecret != nil || a.State != nil {
return errors.New("UpdateKey AUMs may only specify KeyID, Votes, and Meta")
}
case AUMCheckpoint:
if a.State == nil {
return errors.New("Checkpoint AUMs must specify the state")
}
if a.KeyID != nil || a.DisablementSecret != nil || a.Key != nil || a.Votes != nil || a.Meta != nil {
return errors.New("Checkpoint AUMs may only specify State")
}
case AUMDisableNL:
if len(a.DisablementSecret) == 0 {
return errors.New("DisableNL AUMs must specify a disablement secret")
}
if a.KeyID != nil || a.State != nil || a.Key != nil || a.Votes != nil || a.Meta != nil {
return errors.New("DisableNL AUMs may only a disablement secret")
}
}
return nil
}
// Serialize returns the given AUM in a serialized format.
func (a *AUM) Serialize() []byte {
// Why CBOR and not something like JSON?
//
// The main function of an AUM is to carry signed data. Signatures are
// over digests, so the serialized representation must be deterministic.
// Further, experience with other attempts (JWS/JWT,SAML,X509 etc) has
// taught us that even subtle behaviors such as how you handle invalid
// or unrecognized fields + any invariants in subsequent re-serialization
// can easily lead to security-relevant logic bugs. Its certainly possible
// to invent a workable scheme by massaging a JSON parsing library, though
// profoundly unwise.
//
// CBOR is one of the few encoding schemes that are appropriate for use
// with signatures and has security-conscious parsing + serialization
// rules baked into the spec. We use the CTAP2 mode, which is well
// understood + widely-implemented, and already proven for use in signing
// assertions through its use by FIDO2 devices.
out := bytes.NewBuffer(make([]byte, 0, 128))
encoder, err := cbor.CTAP2EncOptions().EncMode()
if err != nil {
// Deterministic validation of encoding options, should
// never fail.
panic(err)
}
if err := encoder.NewEncoder(out).Encode(a); err != nil {
// Writing to a bytes.Buffer should never fail.
panic(err)
}
return out.Bytes()
}
// Hash returns a cryptographic digest of all AUM contents.
func (a *AUM) Hash() AUMHash {
return blake2s.Sum256(a.Serialize())
}
// SigHash returns the cryptographic digest which a signature
// is over.
//
// This is identical to Hash() except the Signatures are not
// serialized. Without this, the hash used for signatures
// would be circularly dependent on the signatures.
func (a AUM) SigHash() AUMSigHash {
dupe := a
dupe.Signatures = nil
return blake2s.Sum256(dupe.Serialize())
}
// Parent returns the parent's AUM hash and true, or a
// zero value and false if there was no parent.
func (a *AUM) Parent() (h AUMHash, ok bool) {
if len(a.PrevAUMHash) > 0 {
copy(h[:], a.PrevAUMHash)
return h, true
}
return h, false
}
func (a *AUM) sign25519(priv ed25519.PrivateKey) {
key := Key{Kind: Key25519, Public: priv.Public().(ed25519.PublicKey)}
sigHash := a.SigHash()
a.Signatures = append(a.Signatures, Signature{
KeyID: key.ID(),
Signature: ed25519.Sign(priv, sigHash[:]),
})
}
// TODO(tom): Implement Weight() once a future PR brings in the State type.

197
tka/aum_test.go Normal file
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@ -0,0 +1,197 @@
// 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 (
"bytes"
"testing"
"github.com/fxamacker/cbor/v2"
"github.com/google/go-cmp/cmp"
)
func TestSerialization(t *testing.T) {
uint2 := uint(2)
tcs := []struct {
Name string
AUM AUM
Expect []byte
}{
{
"AddKey",
AUM{MessageKind: AUMAddKey, Key: &Key{}},
[]byte{
0xa3, // major type 5 (map), 3 items
0x01, // |- major type 0 (int), value 1 (first key, MessageKind)
0x01, // |- major type 0 (int), value 1 (first value, AUMAddKey)
0x02, // |- major type 0 (int), value 2 (second key, PrevAUMHash)
0xf6, // |- major type 7 (val), value null (second value, nil)
0x03, // |- major type 0 (int), value 3 (third key, Key)
0xa3, // |- major type 5 (map), 3 items (type Key)
0x01, // |- major type 0 (int), value 1 (first key, Kind)
0x00, // |- major type 0 (int), value 0 (first value)
0x02, // |- major type 0 (int), value 2 (second key, Votes)
0x00, // |- major type 0 (int), value 0 (first value)
0x03, // |- major type 0 (int), value 3 (third key, Public)
0xf6, // |- major type 7 (val), value null (third value, nil)
},
},
{
"RemoveKey",
AUM{MessageKind: AUMRemoveKey, KeyID: []byte{1, 2}},
[]byte{
0xa3, // major type 5 (map), 3 items
0x01, // |- major type 0 (int), value 1 (first key, MessageKind)
0x02, // |- major type 0 (int), value 2 (first value, AUMRemoveKey)
0x02, // |- major type 0 (int), value 2 (second key, PrevAUMHash)
0xf6, // |- major type 7 (val), value null (second value, nil)
0x04, // |- major type 0 (int), value 4 (third key, KeyID)
0x42, // |- major type 2 (byte string), 2 items
0x01, // |- major type 0 (int), value 1 (byte 1)
0x02, // |- major type 0 (int), value 2 (byte 2)
},
},
{
"UpdateKey",
AUM{MessageKind: AUMUpdateKey, Votes: &uint2, KeyID: []byte{1, 2}, Meta: map[string]string{"a": "b"}},
[]byte{
0xa5, // major type 5 (map), 5 items
0x01, // |- major type 0 (int), value 1 (first key, MessageKind)
0x05, // |- major type 0 (int), value 2 (first value, AUMUpdateKey)
0x02, // |- major type 0 (int), value 2 (second key, PrevAUMHash)
0xf6, // |- major type 7 (val), value null (second value, nil)
0x04, // |- major type 0 (int), value 4 (third key, KeyID)
0x42, // |- major type 2 (byte string), 2 items
0x01, // |- major type 0 (int), value 1 (byte 1)
0x02, // |- major type 0 (int), value 2 (byte 2)
0x07, // |- major type 0 (int), value 7 (fourth key, Votes)
0x02, // |- major type 0 (int), value 2 (forth value, 2)
0x08, // |- major type 0 (int), value 8 (fifth key, Meta)
0xa1, // |- major type 5 (map), 1 item (map[string]string type)
0x61, // |- major type 3 (text string), value 1 (first key, one byte long)
0x61, // |- byte 'a'
0x61, // |- major type 3 (text string), value 1 (first value, one byte long)
0x62, // |- byte 'b'
},
},
{
"DisableNL",
AUM{MessageKind: AUMDisableNL, PrevAUMHash: []byte{1, 2}, DisablementSecret: []byte{3, 4}},
[]byte{
0xa3, // major type 5 (map), 3 items
0x01, // |- major type 0 (int), value 1 (first key, MessageKind)
0x03, // |- major type 0 (int), value 3 (first value, AUMDisableNL)
0x02, // |- major type 0 (int), value 2 (second key, PrevAUMHash)
0x42, // |- major type 2 (byte string), 2 items (second value)
0x01, // |- major type 0 (int), value 1 (byte 1)
0x02, // |- major type 0 (int), value 2 (byte 2)
0x06, // |- major type 0 (int), value 6 (third key, DisablementSecret)
0x42, // |- major type 2 (byte string), 2 items (third value)
0x03, // |- major type 0 (int), value 3 (byte 3)
0x04, // |- major type 0 (int), value 4 (byte 4)
},
},
// TODO(tom): Uncomment once a future PR brings in the State type.
// {
// "Checkpoint",
// AUM{MessageKind: AUMCheckpoint, PrevAUMHash: []byte{1, 2}, State: &State{
// LastAUMHash: []byte{3, 4},
// Keys: []Key{
// {Kind: Key25519, Public: []byte{5, 6}},
// },
// }},
// []byte{
// 0xa3, // major type 5 (map), 3 items
// 0x01, // |- major type 0 (int), value 1 (first key, MessageKind)
// 0x06, // |- major type 0 (int), value 6 (first value, AUMCheckpoint)
// 0x02, // |- major type 0 (int), value 2 (second key, PrevAUMHash)
// 0x42, // |- major type 2 (byte string), 2 items (second value)
// 0x01, // |- major type 0 (int), value 1 (byte 1)
// 0x02, // |- major type 0 (int), value 2 (byte 2)
// 0x05, // |- major type 0 (int), value 5 (third key, State)
// 0xa3, // |- major type 5 (map), 3 items (third value, State type)
// 0x01, // |- major type 0 (int), value 1 (first key, LastAUMHash)
// 0x42, // |- major type 2 (byte string), 2 items (first value)
// 0x03, // |- major type 0 (int), value 3 (byte 3)
// 0x04, // |- major type 0 (int), value 4 (byte 4)
// 0x02, // |- major type 0 (int), value 2 (second key, DisablementSecrets)
// 0xf6, // |- major type 7 (val), value null (second value, nil)
// 0x03, // |- major type 0 (int), value 3 (third key, Keys)
// 0x81, // |- major type 4 (array), value 1 (one item in array)
// 0xa3, // |- major type 5 (map), 3 items (Key type)
// 0x01, // |- major type 0 (int), value 1 (first key, Kind)
// 0x01, // |- major type 0 (int), value 1 (first value, Key25519)
// 0x02, // |- major type 0 (int), value 2 (second key, Votes)
// 0x00, // |- major type 0 (int), value 0 (second value, 0)
// 0x03, // |- major type 0 (int), value 3 (third key, Public)
// 0x42, // |- major type 2 (byte string), 2 items (third value)
// 0x05, // |- major type 0 (int), value 5 (byte 5)
// 0x06, // |- major type 0 (int), value 6 (byte 6)
// },
// },
{
"Signature",
AUM{MessageKind: AUMAddKey, Signatures: []Signature{{KeyID: []byte{1}}}},
[]byte{
0xa3, // major type 5 (map), 3 items
0x01, // |- major type 0 (int), value 1 (first key, MessageKind)
0x01, // |- major type 0 (int), value 1 (first value, AUMAddKey)
0x02, // |- major type 0 (int), value 2 (second key, PrevAUMHash)
0xf6, // |- major type 7 (val), value null (second value, nil)
0x17, // |- major type 0 (int), value 22 (third key, Signatures)
0x81, // |- major type 4 (array), value 1 (one item in array)
0xa2, // |- major type 5 (map), 2 items (Signature type)
0x01, // |- major type 0 (int), value 1 (first key, KeyID)
0x41, // |- major type 2 (byte string), 1 item
0x01, // |- major type 0 (int), value 1 (byte 1)
0x02, // |- major type 0 (int), value 2 (second key, Signature)
0xf6, // |- major type 7 (val), value null (second value, nil)
},
},
}
for _, tc := range tcs {
t.Run(tc.Name, func(t *testing.T) {
data := tc.AUM.Serialize()
if diff := cmp.Diff(tc.Expect, data); diff != "" {
t.Errorf("serialization differs (-want, +got):\n%s", diff)
}
var decodedAUM AUM
if err := cbor.Unmarshal(data, &decodedAUM); err != nil {
t.Fatalf("Unmarshal failed: %v", err)
}
if diff := cmp.Diff(tc.AUM, decodedAUM); diff != "" {
t.Errorf("unmarshalled version differs (-want, +got):\n%s", diff)
}
})
}
}
func TestAUMHashes(t *testing.T) {
// .Hash(): a hash over everything.
// .SigHash(): a hash over everything except the signatures.
// The signatures are over a hash of the AUM, so
// using SigHash() breaks this circularity.
aum := AUM{MessageKind: AUMAddKey, Key: &Key{Kind: Key25519}}
sigHash1 := aum.SigHash()
aumHash1 := aum.Hash()
aum.Signatures = []Signature{{KeyID: []byte{1, 2, 3, 4}}}
sigHash2 := aum.SigHash()
aumHash2 := aum.Hash()
if len(aum.Signatures) != 1 {
t.Error("signature was removed by one of the hash functions")
}
if !bytes.Equal(sigHash1[:], sigHash1[:]) {
t.Errorf("signature hash dependent on signatures!\n\t1 = %x\n\t2 = %x", sigHash1, sigHash2)
}
if bytes.Equal(aumHash1[:], aumHash2[:]) {
t.Error("aum hash didnt change")
}
}

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// 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)
}
}

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// 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 (
"bytes"
"crypto/ed25519"
"encoding/binary"
"math/rand"
"testing"
)
// returns a random source based on the test name + extraSeed.
func testingRand(t *testing.T, extraSeed int64) *rand.Rand {
var seed int64
if err := binary.Read(bytes.NewBuffer([]byte(t.Name())), binary.LittleEndian, &seed); err != nil {
panic(err)
}
return rand.New(rand.NewSource(seed + extraSeed))
}
// generates a 25519 private key based on the seed + test name.
func testingKey25519(t *testing.T, seed int64) (ed25519.PublicKey, ed25519.PrivateKey) {
pub, priv, err := ed25519.GenerateKey(testingRand(t, seed))
if err != nil {
panic(err)
}
return pub, priv
}
func TestVerify25519(t *testing.T) {
pub, priv := testingKey25519(t, 1)
key := Key{
Kind: Key25519,
Public: pub,
}
aum := AUM{
MessageKind: AUMRemoveKey,
KeyID: []byte{1, 2, 3, 4},
// Signatures is set to crap so we are sure its ignored in the sigHash computation.
Signatures: []Signature{{KeyID: []byte{45, 42}}},
}
sigHash := aum.SigHash()
aum.Signatures = []Signature{
{
KeyID: key.ID(),
Signature: ed25519.Sign(priv, sigHash[:]),
},
}
if err := aum.Signatures[0].Verify(aum.SigHash(), key); err != nil {
t.Errorf("signature verification failed: %v", err)
}
// Make sure it fails with a different public key.
pub2, _ := testingKey25519(t, 2)
key2 := Key{Kind: Key25519, Public: pub2}
if err := aum.Signatures[0].Verify(aum.SigHash(), key2); err == nil {
t.Error("signature verification with different key did not fail")
}
}

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// 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 (WIP) implements the Tailnet Key Authority.
package tka