life is too short for a diary



Mar 2016

Find kth largest element in an array

The other day I stumble upon the question to find the kth largest element in the array. At first glance, I thought the solution was trivial. But later I thought that there are multiple ways to achieve efficient solution.


Apr 2013

Encrypted Files in Minix 3

Implemented a new system call in Minix 3 along with the library function that allows it to be called conveniently from a C program. The library interface extends extends file access operations to handle encrypted files.

Reading and writing to a file is done through a system call. The first is to access the “master encryption table” file (/etc/encryptTable) that stores the information about every file that is encrypted within Minix and contains three pieces of information: fs_dev, inode_nr and hashed_pw. The first two information uniquely identifies what file is encrypted and can be obtained from the vnode for the file.


Mar 2013

Binary Sempahore

Implemented binary semaphore in Minix 3. Minix 3 is a micro-kernel operating system.

Most of the process pass information among themselves using application IPC. This often result in race condition. To prevent it and provide synchronization, semaphores, first proposed by Dikstras, is used.


Nov 2012

Advanced Encryption Standard (AES)

Advanced Encryption Standard, a symmetric key algorithm, implemented in C++. All the parties use the same key for encryption and decryption. It has superseded DES, another symmetric key algorithms.


Aug 2012

Data Encryption Standard (DES)

Data Encryption Standard, a symmetric key algorithm, implemented in C++. All the parties use the same key for encryption and decryption. Look at the diagram below.

Here, m is message which is passed through an encrypted function E along with key K. The resultant is a unintelligent gibberish cipher. The cipher is decoded again using the same key to produce plain message.