Two Rules and Brute - Force Attack

For any algorithm that is used for Cryptography, it must satisfy the two conditions or at the minimum one condition must atleast be satisfied.

They are:

1. The cost of breaking the Cipher should exceed the value of the Encrypted Information.

2. The time required to break the cipher should exceed the useful lifetime of the information.


Brute-Force Attack:


The method of using all the possible keys to get the intelligent plain text from cipher text is called the Brute-Force Attack.

This is the most commonly used attack.

For example: If a encryption method is performed with a key length of 2 bits, then there is a possibility of 4 keys.

in general this is represented as:

if the key length is of "n" bits,

then,

the number of possible keys is equal to 2^n.

dimensions of cryptography

With the use of Symmetric encryption, the principle security problem is maintaining the secrecy of the key..

Cryptology is the combination of Cryptography and Cryptanalys

There are 3 dimensions for cryptography:

1. Type of operation used for transforming plaintext to ciphertext.

In this there are two methods:

• Substitution - which means each element in the plain text is mapped into another element.
• Transposition - which means each element in the plain text is rearranged.

Most of the systems, which are also referred as product systems, involve multiple stages of substitution and transpositions.


2. Number of keys used.

if the same key is used by the sender and the receiver then it is called symmetric/single-key/secret-key/conventional encryption.


3. The way in which the plaintext is processed.

i.e. whether the data is processed in form of blocks (block cipher) or continuously (stream cipher)

Basic words

Let us understand some of the basic words used in cryptography..


1. Plain Text: An original Message which is used is called plain text.

2. Cipher Text: The encrypted message that is obtained when we encrypt the plain text is called cipher text.

3. Enciphering or Encryption: The process of converting from plain text to cipher text.

4. Deciphering or Decryption: The process of restoring the plain text from the cipher text.

5. Cryptanalysis: The techniques used for deciphering a message without any knowledge of the enciphering details.


Attacks on Encryption Algorithms:

The main objective of any attack on the cipher text would be to recover the key in the use rather than simply to recover the plain text. There are generally 2 approaches for this:

• Cryptanalysis : based on the properties of encryption algorithm.

• Brute-force attacks : The attacker tries all possible keys on a piece of cipher text.

History

CRYPTOGRAPHY
CRYPTOGRAPHY
CRYPTOGRAPHY
CRYPTOGRAPHY

Brief History:

Cryptography (or cryptology; derived from Greek κρυπτός kryptós "hidden," and γράφειν gráfein "to write") is a discipline of mathematics concerned with information security.

The History of Cryptography begins thousands of years ago. The earliest known use of cryptography is found in non-standard hieroglyphs carved into monuments from Egypt's Old Kingdom (ca 4500+ years ago). These are not thought to be serious attempts at secret communications, however, but rather to have been attempts at mystery, intrigue, or even amusement for literate onlookers.

Although cryptography has a long and complex history, it wasn't until the 19th century that it developed anything more than ad hoc approaches to either encryption or cryptanalysis (the science of finding weaknesses in crypto systems).

In 1917, Gilbert Vernam proposed a teletype cipher in which a previously-prepared key, kept on paper tape, is combined character by character with the plaintext message to produce the cyphertext. This led to the development of the one time pad and the use of electromechanical devices as cipher machines.

By World War II, mechanical and electromechanical cipher machines were in wide use, although — where such machines were impractical — manual systems continued in use. Great advances were made in cipher-breaking, all in secrecy. Information about this period has begun to be declassified as the official British 50-year secrecy period has come to an end, as U.S. archives have slowly opened, and as assorted memoirs and articles have appeared.


Some pictures of early machines used for Cryptography:

The Enigma machine was widely used by Nazi Germany; its cryptanalysis by the Allies provided vital Ultra intelligence.