In cryptography, a

**brute-force attack**, or**exhaustive key search**, is a strategy that can, in theory, be used against any encrypted data.[1] Such an attack might be utilized when it is not possible to take advantage of other weaknesses in an encryption system (if any exist) that would make the task easier. It involves systematically checking all possible keys until the correct key is found. In the worst case, this would involve traversing the entiresearch space.
The key length used in the encryption determines the practical feasibility of performing a brute-force attack, with longer keys exponentially more difficult to crack than shorter ones. Brute-force attacks can be made less effective by obfuscating the data to be encoded, something that makes it more difficult for an attacker to recognise when he/she has cracked the code. One of the measures of the strength of an encryption system is how long it would theoretically take an attacker to mount a successful brute-force attack against it.

Brute-force attacks are an application of brute-force search, the general problem-solving technique of enumerating all candidates and checking each one.

**UNBREAKABLE CODES.**

Certain types of encryption, by their mathematical properties, cannot be defeated by brute force. An example of this is one-time pad cryptography, where every cleartext bit has a corresponding key bit. One-time pads rely on the ability to generate a truly random sequence of key bits. A brute-force attack would eventually reveal the correct decoding, but also every other possible combination of bits, and would have no way of distinguishing one from the other. A small, 100-byte, one-time-pad–encoded string subjected to a brute-force attack would eventually reveal every 100-byte string possible, including the correct answer, but mostly nonsense. Of all the answers given, there is no way of knowing which is the correct one. Nevertheless, the system can be defeated if not implemented correctly, for example if one-time pads are re-used or intercepted.[12]

A similar argument can apply when a *single* plaintext is encrypted by any method where the text is shorter than the key. For example, if the text is a single byte, then (for most types of encryption with large key sizes such as 128 bits) all bytes from "00"-"FF" will appear, with equal probability, as possible plaintexts corresponding to guessed keys.

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**Wikipedia.Inc(Wikimedia Foundation)**

**KANISHK**

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