Golang Vanity v3 Onion Address Generator

onion-address-gen.go

package main

import (
	"crypto"
	"crypto/ed25519"
	"encoding/base32"
	"encoding/base64"
	"encoding/hex"
	"flag"
	"fmt"
	"log"
	"os"
	"strings"

	_ "golang.org/x/crypto/sha3"
)

// v3 Onion Address Generator
//
// Do `go build && ./onion-address-gen` and run with the `-prefix` flag to search.
// this will generate hostnames, as well as the necessary public and secret keys
// needed to be able to validate you own the address. matching hostnames will be
// written to `./addresses.txt`.
//
// `./addresses.txt` Format
// const l = line.split(' ')
// l[0]: the index at which this name was found during the run
// l[1]: the onion address
// l[2]: the public key, base64 encoded
// l[3]: the secret key, base64 decoded
//
// in order to use these contents, create a directory. eg: `./tor_site`
// echo "l[1]" | tee ./hostname
// echo "l[2]" | base64 -d | tee ./hs_ed25519_public_key
// echo "l[3]" | base64 -d | tee ./hs_ed25519_secret_key
//
// std-lib required to implement this in another language
// os.Create: File
// fmt.Fprintln
// String.HasPrefix
// fmt.Println
// ed25519.GenerateKey
// crypto.SHA3_256.New
// hex.Encode
// base32.Encode
// base64.Encode

func main() {
	prefix := flag.String("prefix", "", "Prefix for the vanity hostname you wish to discover")
	flag.Parse()
	f, _ := os.OpenFile("./addresses.txt", os.O_WRONLY|os.O_CREATE|os.O_APPEND, os.ModePerm)
	n := 0
	for true {
		n++
		adr, pb, pv := newAddress()
		if strings.HasPrefix(adr, *prefix) {
			fmt.Fprintln(f, n, adr, doBase64(pb), doBase64(pv))
			log.Println(n, adr)
		}
	}
}

func newAddress() (string, string, string) {
	pub, prv, _ := ed25519.GenerateKey(nil)
	version := "\x03"
	key := string(pub)
	checksum := h(".onion checksum" + key + version)[:2]
	addr := doBase32(key + checksum + version)
	keyPub := "== ed25519v1-public: type0 ==" + "\x00\x00\x00" + string(pub)
	keyPrv := "== ed25519v1-secret: type0 ==" + "\x00\x00\x00" + string(prv)
	return addr + ".onion", keyPub, keyPrv
}

func h(d string) string {
	a := crypto.SHA3_256.New()
	a.Write([]byte(d))
	b := hex.EncodeToString(a.Sum([]byte{}))
	return b
}

func doBase32(d string) string {
	return strings.ToLower(base32.StdEncoding.EncodeToString([]byte(d)))
}

func doBase64(d string) string {
	return base64.StdEncoding.EncodeToString([]byte(d))
}

Here is a ready to use onion generator https://github.com/rdkr/oniongen-go
See also my fork that have some optimizations https://github.com/stokito/oniongen-go/tree/prefix
I sent PRs to rdkr/oniongen-go but not sure when they'll be merged

Also it looks like you are missing one thing
https://github.com/rdkr/oniongen-go/blob/master/main.go#L38=