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RSA implemented in Python

March 31st, 2011 • Comments Off on RSA implemented in Python

Just needed to work through some algorithms lately. Best book/reference in that area is most probably the third edition of Introduction to Algorithms. Here is some python code with references to the pages in this book describing the RSA algorithm: 

#!/usr/bin/python

def euclid(a, b):
    """
    Taken from page 935
    """

    if b == 0:
        return a
    else:
        return euclid(b, a % b)

def extended_euclid(a, b):
    """
    Taken form page 937
    """
    if b == 0:
        return [a, 1, 0]
    else:
        previous_d, previous_x, previous_y = extended_euclid(b, a % b)
        d, x, y = (previous_d, previous_y, previous_x - a // b * previous_y)
        return [d, x, y]

def generate_keys(p, q):
    """
    Generation of public and private keys...
    """

    n = p * q
    m = (p - 1) * (q - 1)

    e = long(2)
    while e < m:
        if euclid(e, m) == 1:
            break
        else:
            e = e + 1

    dd, x, y = extended_euclid(m, e)
    if y > 0:
        d = y
    else:
        d = y % m

    return [(e, n), (d, n)]

def rsa(p, q, msg):
    """
    RSA walkthrough - Taken from page 962
    """
    pub_key, priv_key = generate_keys(p, q)

    print 'Public Key: ', pub_key
    print 'Private Key: ', priv_key

    e, n = pub_key
    d, n = priv_key

    crypted = (msg ** e) % n
    print 'Crypted value is: ', crypted

    original = crypted ** d % n
    print 'The original number was: ', original

if __name__ == "__main__":
    p = long(raw_input('First prime: '))
    q = long(raw_input('Second prime: '))

    msg = long(raw_input('Number to test rsa with: '))

    rsa(p, q, msg)

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My Software Development Environment for Python

February 21st, 2011 • Comments Off on My Software Development Environment for Python

Python is my favorite programming language for multiple reasons. Most important though is that it has a strong community, a Benevolent Dictator For Life (BDFL) and allows rapid development of high quality software. I love automation of processes wherever possible because it saves time. Here is a list of tools, methodologies, stuff I use to ensure code quality:

Tools I sometimes use during the development of code:

Thinks I would like to have replacements for:

Overall I’m pretty happy with this setup and find it good for fast coding. I usually write unittests (With test for success, failure and sanity for every routine) first before starting coding. I don’t find it a time waste but actually I’m pretty sure that the overall setup allows me to code and refactor faster.

Maybe others or you (?) also want to writeup their setups and we can start a site like The Setup for Software Development? Please Retweet and share the link!

Update: Also have a look at this Python and Dtrace blog post.

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OCCI and More

November 15th, 2010 • Comments Off on OCCI and More

Busy times – but this post nicely wraps up what is going on regarding OCCI!

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Hudson and Python

September 23rd, 2010 • 3 Comments

Regarding Continuous Integration (CI) systems I probably still like Hudson! Great tool and runs perfectly well. Just get the latest jar file and run it with java – jar hudson.jar. Now to get started you will need to install some plugins:

You can install those plugins in he management interface of hudson. When configuring the job in hudson you simple add a new “Build a free-style software project” job. Add SCM information – and than add some build steps. I had to use two:

python setup.py clean --all
python setup.py build
coverage erase
nosetests --with-coverage --cover-package=<your packages> --with-xunit
coverage xml

And a second one:

#!/bin/bash
pylint -f parseable <your packages> > pylint.txt
echo "pylint complete"

Both are external scripts. Now in the post-build section activate the JUnit test reporting and tell it to use the **/nosetests.xml file. Also activate the Cobertura Coverage report and tell it to use **/coverage.xml. Finally activate the Report Violations – and add pylint.txt in the right row.

Configure the rest of the stuff just as you like and hit the Build button. Thanks to XML the reporting tools written for java can parser the output generated for your Python project. Now you have nice reports from a Python project in Hudson!

A more detailed and great article about this topic can be found here.

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Call graphs for python

September 9th, 2010 • 1 Comment

I’m a big fan of reporting be it reports form automated builds, coverages, API documents etc. To evaluate the python code I’m currently working on I needed Call Graph for Python. After some searching and testing I found this package to be most convenient: http://pycallgraph.slowchop.com/

P.S. If you are running Ubuntu (or similar) a sudo apt-get install python-pycallgraph will install the package. To create the graph simple call: pycallgraph –include=<whatever you need> <your app.py>

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