In this post, I’d like to introduce how to intall Python module fifi-python, a library for finite field arithmetics, provided by Steinwurf.

1. Fifi

Fifi is a library for finite field arithmetics, developed by Steinwurf company. It provides Python wrappers for fifi (written in C++), which is so-called fifi-python.

2. Authenticate to GitHub

Following the installation guide of README.rst in fifi-python, I encountered the issue of “Permission denied (publickey)”.

$ git clone git@github.com:steinwurf/fifi-python.git
Cloning into 'fifi-python'...
Permission denied (publickey).
fatal: Could not read from remote repository.

A “Permission denied” error means that the server rejected my connection. To connect to GitHub with SSH, I need to configure SSH authentication first.

Step 1: Generate a new SSH key

$ cd ~/.ssh && ssh-keygen
Generating public/private rsa key pair.
Enter file in which to save the key (/Users/sparkandshine/.ssh/id_rsa): 
Enter passphrase (empty for no passphrase): 
Enter same passphrase again: 
Your identification has been saved in /Users/sparkandshine/.ssh/id_rsa.
Your public key has been saved in /Users/sparkandshine/.ssh/id_rsa.pub.
The key fingerprint is:
...
The key's randomart image is:
...

Step 2: Add the new SSH key to the GitHub account

Copy the contents of the id_rsa.pub file to your clipboard,

# macOS
$ cat id_rsa.pub | pbcopy

# Linux
$ cat id_rsa.pub | xclip

# Windows (via Cygwin/Git Bash)
$ cat id_rsa.pub | clip

Then, follow the instruction of Authenticating to GitHub / Adding a new SSH key to your GitHub account and add the new SSH key (in the clipboard) to my GitHub account.

Step 3: Test the SSH connection

$ ssh -T git@github.com
Hi sparkandshine! You've successfully authenticated, but GitHub does not provide shell access.

3. Install fifi-python

Request a license

A valid license is required to use this library. Obtain a license by filling out a license request form (here). It is free for non-commercial research and teaching.

Download the repository

$ git clone git@github.com:steinwurf/fifi-python.git
Cloning into 'fifi-python'...
remote: Counting objects: 292, done.
remote: Total 292 (delta 0), reused 0 (delta 0), pack-reused 292
Receiving objects: 100% (292/292), 355.21 KiB | 286.00 KiB/s, done.
Resolving deltas: 100% (158/158), done.
Checking connectivity... done.

Build from source

$ cd fifi-python/
$ python waf configure
...
'configure' finished successfully (3.588s)

$ python waf build
...
[108/108] Linking build/darwin/src/fifi_python/fifi.so
Waf: Leaving directory `/Users/sparkandshine/git/fifi-python/build/darwin'
'build' finished successfully (1m40.314s)

Execute the test case

su-macbook:fifi-python sparkandshine$ cd examples/                  
su-macbook:examples sparkandshine$ python hello_fifi.py 
13 + 7 = 10
13 - 7 = 10
13 * 7 = 5
13 / 7 = 8
~13 = 4

Using PYTHONPATH

Add fifi.so (under build/platform/src/fifi_python/) to PYTHONPATH,

# Add the following line to `~/.profile`
export PYTHONPATH='/Users/sparkandshine/git/fifi-python/build/darwin/src/fifi_python/'

# Make it effect
$ source ~/.bash_profile 

This doen’t work for me. Instead, to make fifi work outsider the folder of fifi-python/, I copy fifi.so (which is located in fifi-python/build/darwin/src/fifi_python/) next to my python file. It works for me.

cp /Users/sparkandshine/git/fifi-python/build/darwin/src/fifi_python/fifi.so git/mathematics/abstract_algebra/finite_field/

References:
[1] StackOverflow: Git – Permission denied (publickey)
[2] Authenticating to GitHub / Connecting to GitHub with SSH
[3] Authenticating to GitHub / Error: Permission denied (publickey)

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