How to verify a .Onion domain against a private key

Question

I am working on a project that will basically sell .Onion (TOR) domain names. The process of generating the domains is similar to mining bitcoins - RSA private keys are generated en mass and if one randomly matches something in my wordlist - then it gets saved off somewhere and added to a database.

The problem here is that this is still a slow process to do solo - so in order for me to try and make it a collaborate exercise - I want to create an online API / Rest API that will allow people to upload their domains and private keys for them to sell on the site.

The problem is - I don't quite know how to verify their domain name against the private key.

Eg: They would be providing a domain like

abcdabcdabcdabcd.onion

and the key would be: -----BEGIN RSA PRIVATE KEY----- MIICXQIBAAKBgQCb+wlPxR8VoUJsYcEFsPX+LfB3jorW9QlH1N38itQvMs0RyTCB +c7hfYQH2f8Z67lobWvveYct51ykhB8n3AluMYIF3OxGlmQJuMIFQmKFryLexzPj LEPREB7+KmeL9Sx1sL4a2Z0qJL4501Ij0T5C3cDEMOvUQBpBttpuUbj1RQIEZTIY AQKBgBwWDEMOYKaSO17xJRuf32CDYJcDKtkJ1GlWROHxREo68J+74DqF55rnoYl/ 4OkfjUMA2WjjjASVRmviBD79vni3eB9MFNzDEMOYa6EIyo1vDEMOzEnfrszkPGEj vOCHbDiG/FlZsCKsADEMOEAuAUQ3W8669Du4FrO9/al+1IudhAkEAy+KBk8HFsO8Z UttdlsLt8//l+NbEMmWF/I588EGyYWUuPUVJd5Xv6iSaDMdecjeW/xf4Wja5C91n lCfb/lxhsQJBAMPZ2fzcUpyKhk6JretSyoq0iVQCO5Pn/0QwTwRUbKreXnnVBYY+ uco2ocfRwsmVK4LUwPgict5qw10bZfl8vdUCQATUV/S0zNc+DEMOw/7p5oJk5hwa +Hrhcf5aVw1AOqySGs0e9V+qDYIjrbkg/BDEMOD00bTTV9a9h3poFrm+DEMOQF2t lgqYbgDEMOZbE+PgebFB6swKfx9Px7+PnNsBK+Mld6pRyldfQ2DEMOr/cy4JQDYA oyX51SNWUMJzkYgeMEUCQQC8i6b3e06B9+++NGADEMO9F5KhlDr1wwSQqnNccDX5 N5vnlhJ/0DGxIMm/bP1ZPUK4/bmvKjNYd7D8zuz2cPor -----END RSA PRIVATE KEY-----

Could someone point me in the direction of some .Net code that can take a private key, and verify that the domain also provided is authentic? https://github.com/lachesis/scallion This github project (one of the tools I use - has the code to 'generate' the domains and private keys - I am just not sure how to perform the verification after the fact)

Answer 1

Never got an answer for this, but I did find a way, using Scallions on source code to verify a Private Key against an Onion Address.

RSAWrapper rsaWrapper = new RSAWrapper("d:\\pk.txt");
Console.WriteLine(rsaWrapper.OnionHash);

Not ideal - as it requires the private key. Inside the RSAWrapper - it does some unsafe code to do 'something' to the public key to determine a DER encoded value. This is the important part of getting the onion address.

public string OnionHash
        {
            get {
                return tobase32str(this.get_der_hash(),10);
            }
        }

private byte[] get_der_hash()
        {
            var sha1 = new System.Security.Cryptography.SHA1Managed();
            return sha1.ComputeHash(this.DER);
            //return tobase32str(hash);
        }


public byte[] DER {
            get {
                byte[] der;
                int buf_size = Rsa.Size + 100;
                int size = 0;
                unsafe // must be a better way to do this!
                {
                    IntPtr hglob = Marshal.AllocHGlobal(buf_size);
                    void* ptr = hglob.ToPointer();
                    void** ptr2 = &ptr;

                    size = Native.i2d_RSAPublicKey(Rsa.Handle, (byte**)ptr2);
                    if(size > buf_size)
                        throw new IndexOutOfRangeException("DER was too large!");

                    der = new byte[size];
                    Marshal.Copy(hglob,der,0,size);
                    Marshal.FreeHGlobal(hglob);
                }
                return der;
            }
        }

Edit - Woot : Looks like the RSAWrapper class is very cohesive and modular. I was able to copy it out - it only needs access to the OpenSSL library, and it also has an RSA.FromPublicKey(string s); method for creating the RSA.

So now, I am able to do

    RSAWrapper rsaWrapper = new RSAWrapper("d:\\pubkey.txt", true);
    Console.WriteLine(rsaWrapper.OnionHash);

Took a few months - but got a better answer than I set out to get. Now I can take public keys, and verify that the Onion address matches the public key. This would verify ownership of an Onion address, without the risk of having to send a private key across the network.