| 1 | // Package relay is the platform STUN/TURN relay: the app-facing credential |
| 2 | // contract (spec §2), key derivation (§4), and the server (§3). |
| 3 | package relay |
| 4 | |
| 5 | import ( |
| 6 | "crypto/hmac" |
| 7 | "crypto/sha256" |
| 8 | "encoding/base64" |
| 9 | "fmt" |
| 10 | "io" |
| 11 | "regexp" |
| 12 | "strconv" |
| 13 | "strings" |
| 14 | "time" |
| 15 | |
| 16 | "golang.org/x/crypto/hkdf" |
| 17 | ) |
| 18 | |
| 19 | const ( |
| 20 | MaxCredentialLife = 4 * time.Hour |
| 21 | hkdfSalt = "carlos-relay-v1" |
| 22 | ) |
| 23 | |
| 24 | var ( |
| 25 | expiryRe = regexp.MustCompile(`^[0-9]+$`) |
| 26 | accountRe = regexp.MustCompile(`^[a-z0-9]+$`) |
| 27 | appRe = regexp.MustCompile(`^[a-z][a-z0-9-]{0,31}$`) |
| 28 | incarnationRe = regexp.MustCompile(`^[0-9a-f]{16}$`) |
| 29 | kidRe = regexp.MustCompile(`^[a-z0-9]{1,8}$`) |
| 30 | ) |
| 31 | |
| 32 | // DeriveKey is HKDF-SHA256(master, salt "carlos-relay-v1", |
| 33 | // info account||0x00||app||0x00||incarnation, 32). |
| 34 | func DeriveKey(master []byte, account, app, incarnation string) []byte { |
| 35 | info := []byte(account + "\x00" + app + "\x00" + incarnation) |
| 36 | r := hkdf.New(sha256.New, master, []byte(hkdfSalt), info) |
| 37 | key := make([]byte, 32) |
| 38 | if _, err := io.ReadFull(r, key); err != nil { |
| 39 | panic("relay: hkdf: " + err.Error()) // cannot fail for 32 bytes |
| 40 | } |
| 41 | return key |
| 42 | } |
| 43 | |
| 44 | // ValidKid reports whether s is usable as a key id: 1-8 lowercase letters or |
| 45 | // digits, the same alphabet ParseUsername and ParseMasters hold a kid to. |
| 46 | // Exported so a WRITER of masters — `carlos relay keygen`, and the console |
| 47 | // parsing its own CARLOS_RELAY_MASTERS_<REGION> — refuses a typo where the |
| 48 | // operator can still fix it, instead of minting usernames every relay |
| 49 | // silently declines. |
| 50 | func ValidKid(s string) bool { return kidRe.MatchString(s) } |
| 51 | |
| 52 | func Suffix(account, app, incarnation, kid string) string { |
| 53 | return account + ":" + app + ":" + incarnation + ":" + kid |
| 54 | } |
| 55 | |
| 56 | // Credential is base64(HMAC-SHA256(key, username)), the TURN password. |
| 57 | func Credential(key []byte, username string) string { |
| 58 | h := hmac.New(sha256.New, key) |
| 59 | h.Write([]byte(username)) |
| 60 | return base64.StdEncoding.EncodeToString(h.Sum(nil)) |
| 61 | } |
| 62 | |
| 63 | type Username struct { |
| 64 | Expiry time.Time |
| 65 | Account, App, Incarnation, Kid string |
| 66 | } |
| 67 | |
| 68 | // ParseUsername splits "<expiry>:<account>:<app>:<incarnation>:<kid>" and |
| 69 | // validates each field's alphabet. It does not check expiry against now; |
| 70 | // the auth handler does that with its own clock. |
| 71 | func ParseUsername(s string) (Username, error) { |
| 72 | f := strings.Split(s, ":") |
| 73 | if len(f) != 5 { |
| 74 | return Username{}, fmt.Errorf("relay: username has %d fields, want 5", len(f)) |
| 75 | } |
| 76 | if !expiryRe.MatchString(f[0]) { |
| 77 | return Username{}, fmt.Errorf("relay: bad expiry %q", f[0]) |
| 78 | } |
| 79 | exp, err := strconv.ParseInt(f[0], 10, 64) |
| 80 | if err != nil { |
| 81 | return Username{}, fmt.Errorf("relay: bad expiry %q", f[0]) |
| 82 | } |
| 83 | switch { |
| 84 | case !accountRe.MatchString(f[1]): |
| 85 | return Username{}, fmt.Errorf("relay: bad account %q", f[1]) |
| 86 | case !appRe.MatchString(f[2]): |
| 87 | return Username{}, fmt.Errorf("relay: bad app %q", f[2]) |
| 88 | case !incarnationRe.MatchString(f[3]): |
| 89 | return Username{}, fmt.Errorf("relay: bad incarnation %q", f[3]) |
| 90 | case !kidRe.MatchString(f[4]): |
| 91 | return Username{}, fmt.Errorf("relay: bad kid %q", f[4]) |
| 92 | } |
| 93 | return Username{Expiry: time.Unix(exp, 0).UTC(), Account: f[1], App: f[2], Incarnation: f[3], Kid: f[4]}, nil |
| 94 | } |
| 95 | |
amadan