Simple telegram invite link unhasher, to retrieve the link creator and group id.

inviteLinkUnhash.go

import (
	"bytes"
	"encoding/base64"
	"encoding/binary"
	"fmt"
)

// hash is the hash at the end of an invite link -> t.me/joinchat/<hash>
func unpack_invitehash(hash string) (int, int, error) {
	fmt.Println("hash:", hash)

	s, err := base64.RawURLEncoding.DecodeString(hash)
	if err != nil {
		return 0, 0, err
	}
	
	if len(s) < 16 { // uint32 (4B) * 2 + uint64 (8B) -> 16B
		return 0, 0, fmt.Errorf("invitelink too short")	
	}

	fmt.Println("bytes:", s)

	creator, err := readULong(s[:4])
	if err != nil {
		return 0, 0, err
	}
	fmt.Println("creator:", creator)

	groupid, err := readULong(s[4:8])
	if err != nil {
		return 0, 0, err
	}
	fmt.Println("groupid:", groupid)

	// this is useless and only used by tg to create "unique" links
	rndnumber, err := readULongLong(s[8:16])
	if err != nil {
		return 0, 0, err
	}
	fmt.Println("rnd number:", rndnumber)

	return creator, groupid, nil
}

func readULong(b []byte) (int, error) {
	buf := bytes.NewBuffer(b)
	var x uint32
	err := binary.Read(buf, binary.BigEndian, &x)
	if err != nil {
		return 0, err
	}
	return int(x), nil
}

func readULongLong(b []byte) (int, error) {
	buf := bytes.NewBuffer(b)
	var x uint64
	err := binary.Read(buf, binary.BigEndian, &x)
	if err != nil {
		return 0, err
	}
	return int(x), nil
}