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// Copyright (c) Tailscale Inc & contributors
// SPDX-License-Identifier: BSD-3-Clause
//go:build !ts_omit_tailnetlock
package tka
import (
"crypto/hmac"
"crypto/sha256"
"encoding/binary"
"encoding/hex"
"fmt"
"net/url"
"strings"
)
const (
DeeplinkTailscaleURLScheme = "tailscale"
DeeplinkCommandSign = "sign-device"
)
// generateHMAC computes a SHA-256 HMAC for the concatenation of components,
// using the Authority stateID as secret.
func (a *Authority) generateHMAC(params NewDeeplinkParams) []byte {
stateID, _ := a.StateIDs()
key := make([]byte, 8)
binary.LittleEndian.PutUint64(key, stateID)
mac := hmac.New(sha256.New, key)
mac.Write([]byte(params.NodeKey))
mac.Write([]byte(params.TLPub))
mac.Write([]byte(params.DeviceName))
mac.Write([]byte(params.OSName))
mac.Write([]byte(params.LoginName))
return mac.Sum(nil)
}
type NewDeeplinkParams struct {
NodeKey string
TLPub string
DeviceName string
OSName string
LoginName string
}
// NewDeeplink creates a signed deeplink using the authority's stateID as a
// secret. This deeplink can then be validated by ValidateDeeplink.
func (a *Authority) NewDeeplink(params NewDeeplinkParams) (string, error) {
if params.NodeKey == "" || !strings.HasPrefix(params.NodeKey, "nodekey:") {
return "", fmt.Errorf("invalid node key %q", params.NodeKey)
}
if params.TLPub == "" || !strings.HasPrefix(params.TLPub, "tlpub:") {
return "", fmt.Errorf("invalid tlpub %q", params.TLPub)
}
if params.DeviceName == "" {
return "", fmt.Errorf("invalid device name %q", params.DeviceName)
}
if params.OSName == "" {
return "", fmt.Errorf("invalid os name %q", params.OSName)
}
if params.LoginName == "" {
return "", fmt.Errorf("invalid login name %q", params.LoginName)
}
u := url.URL{
Scheme: DeeplinkTailscaleURLScheme,
Host: DeeplinkCommandSign,
Path: "/v1/",
}
v := url.Values{}
v.Set("nk", params.NodeKey)
v.Set("tp", params.TLPub)
v.Set("dn", params.DeviceName)
v.Set("os", params.OSName)
v.Set("em", params.LoginName)
hmac := a.generateHMAC(params)
v.Set("hm", hex.EncodeToString(hmac))
u.RawQuery = v.Encode()
return u.String(), nil
}
type DeeplinkValidationResult struct {
IsValid bool
Error string
Version uint8
NodeKey string
TLPub string
DeviceName string
OSName string
EmailAddress string
}
// ValidateDeeplink validates a device signing deeplink using the authority's stateID.
// The input urlString follows this structure:
//
// tailscale://sign-device/v1/?nk=xxx&tp=xxx&dn=xxx&os=xxx&em=xxx&hm=xxx
//
// where:
// - "nk" is the nodekey of the node being signed
// - "tp" is the tailnet lock public key
// - "dn" is the name of the node
// - "os" is the operating system of the node
// - "em" is the email address associated with the node
// - "hm" is a SHA-256 HMAC computed over the concatenation of the above fields, encoded as a hex string
func (a *Authority) ValidateDeeplink(urlString string) DeeplinkValidationResult {
parsedUrl, err := url.Parse(urlString)
if err != nil {
return DeeplinkValidationResult{
IsValid: false,
Error: err.Error(),
}
}
if parsedUrl.Scheme != DeeplinkTailscaleURLScheme {
return DeeplinkValidationResult{
IsValid: false,
Error: fmt.Sprintf("unhandled scheme %s, expected %s", parsedUrl.Scheme, DeeplinkTailscaleURLScheme),
}
}
if parsedUrl.Host != DeeplinkCommandSign {
return DeeplinkValidationResult{
IsValid: false,
Error: fmt.Sprintf("unhandled host %s, expected %s", parsedUrl.Host, DeeplinkCommandSign),
}
}
path := parsedUrl.EscapedPath()
pathComponents := strings.Split(path, "/")
if len(pathComponents) != 3 {
return DeeplinkValidationResult{
IsValid: false,
Error: "invalid path components number found",
}
}
if pathComponents[1] != "v1" {
return DeeplinkValidationResult{
IsValid: false,
Error: fmt.Sprintf("expected v1 deeplink version, found something else: %s", pathComponents[1]),
}
}
nodeKey := parsedUrl.Query().Get("nk")
if len(nodeKey) == 0 {
return DeeplinkValidationResult{
IsValid: false,
Error: "missing nk (NodeKey) query parameter",
}
}
tlPub := parsedUrl.Query().Get("tp")
if len(tlPub) == 0 {
return DeeplinkValidationResult{
IsValid: false,
Error: "missing tp (TLPub) query parameter",
}
}
deviceName := parsedUrl.Query().Get("dn")
if len(deviceName) == 0 {
return DeeplinkValidationResult{
IsValid: false,
Error: "missing dn (DeviceName) query parameter",
}
}
osName := parsedUrl.Query().Get("os")
if len(deviceName) == 0 {
return DeeplinkValidationResult{
IsValid: false,
Error: "missing os (OSName) query parameter",
}
}
emailAddress := parsedUrl.Query().Get("em")
if len(emailAddress) == 0 {
return DeeplinkValidationResult{
IsValid: false,
Error: "missing em (EmailAddress) query parameter",
}
}
hmacString := parsedUrl.Query().Get("hm")
if len(hmacString) == 0 {
return DeeplinkValidationResult{
IsValid: false,
Error: "missing hm (HMAC) query parameter",
}
}
computedHMAC := a.generateHMAC(NewDeeplinkParams{
NodeKey: nodeKey,
TLPub: tlPub,
DeviceName: deviceName,
OSName: osName,
LoginName: emailAddress,
})
hmacHexBytes, err := hex.DecodeString(hmacString)
if err != nil {
return DeeplinkValidationResult{IsValid: false, Error: "could not hex-decode hmac"}
}
if !hmac.Equal(computedHMAC, hmacHexBytes) {
return DeeplinkValidationResult{
IsValid: false,
Error: "hmac authentication failed",
}
}
return DeeplinkValidationResult{
IsValid: true,
NodeKey: nodeKey,
TLPub: tlPub,
DeviceName: deviceName,
OSName: osName,
EmailAddress: emailAddress,
}
}
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