# How does the tor hash-password option work?

I'm trying to write a little python GUI to make interaction with tor control easier on windows, to make using hidden services easier. I'd like to be able to use a password to authenticate, but tor.exe --hash-password mypassword didn't print out anything, and I'd like to be able to hash the password in python anyway.

I looked in main.c and found the function do_hash_password but I don't know which included file to look at to see how all the other functions are used.

First off, if --hash-password doesn't work please file a bug on the bug tracker.

You can check out Stem's integration tests to see how to calculate a password hash using Python.

• --hash-password Does work, but output isn't working. I discovered this by doiing subprocess.check_output(['tor.exe', '--hash-password', 'stuff']) in python. This seems to be a known problem, or at least very similar to an old one I saw mention of online. Thanks for the link to the python stuff! It still doesn't totally explain it though, since it doesn't explain how how is chosen. I can probably figure it out. Mar 17 '15 at 3:17

If you're using Windows PowerShell then try this

tor --hash-password YourPasswordhere | out-file -filepath \path\to\somewhere\filename.txt


https://gitweb.torproject.org/torspec.git/tree/control-spec.txt#n3007

If the 'HashedControlPassword' option is set, it must contain the salted
hash of a secret password.  The salted hash is computed according to the
S2K algorithm in RFC 2440 (OpenPGP), and prefixed with the s2k specifier.
This is then encoded in hexadecimal, prefixed by the indicator sequence
"16:".


Just simple windows command line to generate the HashedControlPassword

or

Here's a quick text explanation on how the password hash generator in Tor works:

1. Obtain 8 random bytes from the system as Salt
2. Append the bytes of the user specified password to the salt
3. Repeat this sequence until the length is 65536 (0x10000) bytes. If repeating the sequence doesn't exactly end up at this number, cut off any excess bytes.
4. Hash the sequence using SHA1
5. Your hashed control password will be "16:" + Hex(Salt) + "60" + Hex(Sha1) where + is string concatenation and Hex() is "convert bytes to uppercase hexadecimal"

## Testing

To test your implementation, use the password "TestPassword12345678" and the Salt 0x72,0x84,0x07,0x51,0xE1,0xEC,0xE7,0x7D

The resulting hash should be 16:72840751E1ECE77D603D8463393DA85D67E7A9746DA4B3533DC7A37178

## Notes

This takes a big shortcut. Namely, the repetition count from step 3 is in reality dynamic.

The formula in use by Tor is count = (16 + (c & 15)) << ((c >> 4) + EXPBIAS);

EXPBIAS is defined as 6 and c is defined as 0x60 (this is the number we insert between the salt and hash in step 5).

Because these numbers are currently constant, the result of the formula is always the same. However, if you make a function that checks the user password against the hash, you don't want to use a constant 0x60 but use the value that is actually in use in the password hash.