A lot of techniques are used to secure a data during communication. There are numbers of encryption algorithms that aims to make the attacker unable to decrypt the data because with increase of encryption algorithms there also emerge new ideas to decrypt the data. There is a competition between the attackers and the users. When we use to encrypt a data they try to invent methods to solve the problem and to make the text understandable. This study of principles/ methods of deciphering cipher text, without knowing the key, is known as cryptanalysis.

Cryptanalysis needs knowledge of different encryption algorithms and some knowledge regarding the plaintext or some sample plaintext-cipher text pair. The attackers also use the method of brute force by applying every possible key to decrypt the data thus it needs a lot of keys to be checked.

When the attacker knows the encryption algorithm & cipher text and additionally knows some sample plaintext-cipher text pairs then there work of analysis gets a bit easier. They attacker may also use plain text and obtain its cipher text to attack the cipher and vice versa. Most basic attacks are proportional to key size that is used in cipher because we have to use that many variations and combinations to find out the exact key.

If we know the basic rules of a language for example the frequency of letter in a specific language then it really works in analysing the basic ciphers. Like the frequency of the letter “t” and “a” etc is much more so check in the encrypted data which letter is occurring more , if that is “w” or “d”, then assume that the key is 3. Now replace the other letters of the cipher text, if they make sense and the converted data is readable then it mean you are succeeded other wise use another key and so on.

A lot of techniques are used to analyse the ciphers and encrypted data and they all have their own methods to deal with cryptanalysis process.