cmd/nodekey: add a tool to print nodekey

cmd/nodekey/nodekey.go

@@ -0,0 +1,85 @@
+package main
+
+import (
+	"fmt"
+	"log"
+	"os"
+
+	"go4.org/mem"
+	"tailscale.com/types/key"
+)
+
+func main() {
+	for _, arg := range os.Args[1:] {
+		k, err := key.ParseNodePublicUntyped(mem.B([]byte(arg)))
+		if err != nil {
+			log.Printf("invalid node key %q: %v", arg, err)
+		}
+		b, err := parseDebug32(arg)
+		if err != nil {
+			log.Printf("invalid debug32 format for %q: %v", arg, err)
+		}
+		k = key.NodePublicFromRaw32(mem.B(b[:]))
+		log.Printf("node key: %s", k.ShortString())
+		log.Printf("node key: %s", k.String())
+	}
+}
+
+// parseDebug32 attempts to reconstruct the first 4 bytes of a key
+// from the Tailscale debug representation like "[abcde]".
+// The remaining bytes will be zero.
+func parseDebug32(s string) ([32]byte, error) {
+	var k [32]byte
+
+	if s == "" {
+		return k, nil
+	}
+	if len(s) != 7 || s[0] != '[' || s[6] != ']' {
+		return k, fmt.Errorf("invalid debug32 format %q", s)
+	}
+
+	decode64 := func(c byte) (byte, bool) {
+		switch {
+		case 'A' <= c && c <= 'Z':
+			return c - 'A', true
+		case 'a' <= c && c <= 'z':
+			return c - 'a' + 26, true
+		case '0' <= c && c <= '9':
+			return c - '0' + 52, true
+		case c == '+':
+			return 62, true
+		case c == '/':
+			return 63, true
+		default:
+			return 0, false
+		}
+	}
+
+	v0, ok := decode64(s[1])
+	if !ok {
+		return k, fmt.Errorf("invalid debug32 format %q", s)
+	}
+	v1, ok := decode64(s[2])
+	if !ok {
+		return k, fmt.Errorf("invalid debug32 format %q", s)
+	}
+	v2, ok := decode64(s[3])
+	if !ok {
+		return k, fmt.Errorf("invalid debug32 format %q", s)
+	}
+	v3, ok := decode64(s[4])
+	if !ok {
+		return k, fmt.Errorf("invalid debug32 format %q", s)
+	}
+	v4, ok := decode64(s[5])
+	if !ok {
+		return k, fmt.Errorf("invalid debug32 format %q", s)
+	}
+
+	k[0] = v0<<2 | v1>>4
+	k[1] = v1<<4 | v2>>2
+	k[2] = v2<<6 | v3
+	k[3] = v4 << 2 // low 2 bits were discarded by debug32
+
+	return k, nil
+}