From the monthly archives: April 2012

A Program for Taking Screenshot for Android Device from Command Line

By On April 30, 2012 · 4 Comments

Android DDMS allows one to take screenshot easily by clicking a button. However, sometimes a developer may want to take screenshot from the command line in order to automate it. This post discusses how we can do this and provides a java program at the end.

0. How DDMS Capture Screenshot

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Big Integer Arithmetic

By On April 4, 2012 · Leave a Comment

Most of computer applications operates on small integers which can be represented by 32 bit integers. However, there are times we’ll need to deal with extremely big integers which can only be represented by hundreds of bits. One of such application is cryptography.

This post gives two simple implementations of the big integer arithmetic. [...]

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Primality Testing — Part 4. Fermat’s Little Theorem and A Probabilistic Approach

By On April 2, 2012 · 1 Comment

Previous posts on primality testing are all trying to factor the input number. For a very large number with few hundreds of bits, it is difficult to compute in that manner.
This post introduce a probabilistic approach based on Fermat’s primality test.

Fermat’s Little Theorem

Fermat’s primality test is based on Fermat’s [...]

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How to Calculate Modular Exponentiation

By On April 2, 2012 · Leave a Comment

Modular exponentiation is a exponentiation performed over modulus. It is used in many cryptographic algorithms.

Modular exponentiation accepts three input integers, say x, y and n and computes according to the formula below,

(x ^ y) mod n

Native Approaches

A naive approach to compute modular exponentiation is to compute the exponentiation first and [...]

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