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https://github.com/stef/libsphinx

Sphinx-based Password Storage low-level library
https://github.com/stef/libsphinx

library password-manager password-storage sphinx

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Sphinx-based Password Storage low-level library

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README 

        
sphinx: a password **S**tore that **P**erfectly **H**ides from **I**tself

(**N**o **X**aggeration)



libsphinx is a cryptographic password storage as described in

https://eprint.iacr.org/2015/1099



and as presented by the Levchin Prize winner 2018 Hugo Krawczyk on

Real World Crypto https://www.youtube.com/watch?v=px8hiyf81iM



## What is this thing?



It allows you to have only a few (at least one) passwords that you

need to remember, while at the same time provides unique 40 (ASCII)

character long very random passwords (256 bit entropy). Your master

password is encrypted (blinded) and sent to the password storage

server which (without decrypting) combines your encrypted password

with a big random number and sends this (still encrypted) back to you,

where you can decrypt it (it's a kind of end-to-end encryption of

passwords) and use the resulting unique, strong and very random

password to register/login to various services. The resulting strong

passwords make offline password cracking attempts infeasible. If say

you use this with google and their password database is leaked your

password will still be safe.



How is this different from my password storage which stores the

passwords in an encrypted database? Most importantly using an

encrypted database is not "end-to-end" encrypted. Your master password

is used to decrypt the database read out the password and send it back

to you. This means whoever has your database can try to crack your

master password on it, or can capture your master password while you

type or send it over the network. Then all your passwords are

compromised. If some attacker compromises your traditional password

store it's mostly game over for you. Using sphinx the attacker

controlling your password store learns nothing about your master nor

your individual passwords. Also even if your strong password leaks,

it's unique and cannot be used to login to other sites or services.



## Installing



Install `libsodium`  and `libsodium-dev` using your operating system provided

package management. 



Building everything should (hopefully) be quite simple afterwards:



```

cd src

make

```



## Library



libsphinx builds a library, which you can use to build your

own password manager either in C/C++ or any other language that can

bind to this library.



### The Sphinx API

The Library exposes the following 3 functions for the FK-PTR protocol

(the password storage):



```

void sphinx_challenge(const uint8_t *pwd, const size_t p_len, uint8_t *bfac, uint8_t *chal);

```

 * pwd, p_len: are input params, containing the master password and its length

 * bfac: is an output param, it's a pointer to an array of

   `SPHINX_255_SCALAR_BYTES` (32) bytes - the blinding factor

 * chal: is an output param, it's a pointer to an array of

   `SPHINX_255_SER_BYTES` (32) bytes - the challenge



```

int sphinx_respond(const uint8_t *chal, const uint8_t *secret, uint8_t *resp);

```

 * chal: is an input param, it is the challenge from the challenge()

   function, it has to be a `SPHINX_255_SER_BYTES` (32) bytes big array

 * secret: is an input param, it is the "secret" contribution from the

   device, it is a `SPHINX_255_SCALAR_BYTES` (32) bytes long array

 * resp: is an output parameter, it is the result of this step, it

   must be a `SPHINX_255_SER_BYTES` (32) byte sized array

 * the function returns 1 on error, 0 on success



```

int sphinx_finish(const uint8_t *pwd, const size_t p_len,

                  const uint8_t *bfac, const uint8_t *resp,

                  uint8_t *rwd);

```



 * pwd: is an input param, it specifies the password again.

 * p_len: is an input param, it specifies the password length

 * bfac: is an input param, it is the bfac output from challenge(),

   it is array of `SPHINX_255_SCALAR_BYTES` (32) bytes

 * resp: is an input parameter, it's the response from respond(), it

   is a `SPHINX_255_SER_BYTES` (32) byte sized array

 * rwd: is an output param, the derived (binary) password, it is a

   `SPHINX_255_SER_BYTES` (32) byte array

 * this function returns 1 on error, 0 on success



## Standalone Binaries



libsphinx comes with very simple binaries implementing the sphinx

protocol, so you can build your own password storage even from shell

scripts.  Each step in the SPHINX protocol is handled by one binary:



### step 1 - challenge

The following creates a challenge for a device:

```

echo -n "shitty master password" | ./challenge >c 2>b

```

The master password is passed in through standard input.



The challenge is sent to standard output.



A blinding factor is stored in a tempfile, the name of this file is output to

stderr. This tempfile is needed in the last step again.



### step 2 - device responds

Pass the challenge from step 1 on standard input like:

```

./respond secret r0

```

The response is sent to standard output.



### step 3 - derive password

To derive a (currently hex) password, pass the response from step 2 on standard

input and the filename of the tempfile and the challenge from step 1 like:



```

fname=$(cat b) ./derive $fname c pwd0

```



The derived password is sent to standard output and currently is a 32

byte binary string. Please note that currently this only outputs the

unblinded H(pwd)^k, for the full protocol this should be hashed again

with the password prepended.



### step 4 - transform into ASCII password



The output from step 3 is a 32 byte binary string, most passwords have some

limitations to accept only printable - ASCII - chars. `bin2pass.py` is a python

script in the [pwdsphinx](https://github.com/stef/pwdsphinx) python module which takes a binary input on standard

input and transforms it into an ASCII password. It can have max two parameters

the classes of characters allowed ([**u**]pper-, [**l**]ower-case letters,

[**d**]igits and [**s**]ymbols) and the size of the password. The following

examples should make this clear:



Full ASCII, max size:

```

./bin2pass.py