To digress a bit, have you ever wondered why you had to study prime numbers in school? I am sure most mathematics teachers do not know this answer. Answer: A subbranch called public-key cryptography which uses prime numbers especially for encrypting e-mails. Over there, they are talking of even bigger numbers like 2048, 4096, 8192 bits.)

When we want to encrypt something, we need to use a cipher. A cipher is just an algorithm similar to a recipe for baking a cake. It has precise, unambiguous steps. To carry out encryption process, you need a key (some called it passphrase). A good practice in cryptography needs key used by a cipher must be of high entropy to be effective.

Data Encryption Standard (DES), introduced as a standard in late 1970's, was most commonly used cipher in 1980's and early 1990's. It uses a 56-bit key. It was broken in late 1990’s with specialized computers costing about US$250,000 in 56 hours. With today's (2005) hardware, it is possible to crack within a day.

Subsequently, Triple-DES superseded DES as logical way to preserve compatibility with earlier investments by big corporations (mainly banks). It uses two 56-bit key using three steps:-

1. Encrypt with Key 1. 2. Decrypt with Key 2. 3. Encrypt with Key 1.

The effective key length used is only 112-bits (equivalent to 34 digits). The key is any number between 0 and 5192296858534827628530496329220095. Some modify last process using Key 3, making it more effective at 168-bit keys.

Advanced Encryption Standard (AES) was adopted as a standard by National Institute of Standards

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