connectivity/tor/torUtils.go

package tor

import (
	"encoding/base32"
	"golang.org/x/crypto/ed25519"
	"golang.org/x/crypto/sha3"
	"strings"
)

// V3HostnameLength is the length of a Tor V3 Onion Address (without the .onion suffix)
const V3HostnameLength = 56

// Hidden service version
const version = byte(0x03)

// Salt used to create checkdigits
const salt = ".onion checksum"

func getCheckdigits(pub ed25519.PublicKey) []byte {
	// Calculate checksum sha3(".onion checksum" || publicKey || version)
	checkstr := []byte(salt)
	checkstr = append(checkstr, pub...)
	checkstr = append(checkstr, version)
	checksum := sha3.Sum256(checkstr)
	return checksum[:2]
}

// GetTorV3Hostname converts an ed25519 public key to a valid tor onion hostname
func GetTorV3Hostname(pub ed25519.PublicKey) string {
	// Construct onion address base32(publicKey || checkdigits || version)
	checkdigits := getCheckdigits(pub)
	combined := pub[:]
	combined = append(combined, checkdigits...)
	combined = append(combined, version)
	serviceID := base32.StdEncoding.EncodeToString(combined)
	return strings.ToLower(serviceID)
}

// IsValidHostname returns true if the given address is a valid onion v3 address
func IsValidHostname(address string) bool {
	if len(address) == V3HostnameLength {
		data, err := base32.StdEncoding.DecodeString(strings.ToUpper(address))
		if err == nil {
			pubkey := data[0:ed25519.PublicKeySize]
			if GetTorV3Hostname(ed25519.PublicKey(pubkey)) == address {
				return true
			}
		}
	}
	return false
}