In my previous article, we learn basics of cryptography. Here we discuss how
hackers attack the system. Hackers main
objective to attack an encryption system is to recover the key in use rather
than simply recovering the actual message of decrypted or ciphertext. There are
two general approaches to attack the encryption system. Those are Cryptanalysis
and Brute-Force Attack.
Cryptanalysis: In this method, hackers rely on the nature of algorithm and some
knowledge about the plain text or some sample plaintext
& ciphertext combinations. This type of attack exploits the characteristics
of the encryption algorithm to find the key or to find the plain text.
There are different
types of Cryptanalysis attacks based on the amount
information cryptanalyst knows. Sometimes cryptanalyst or hackers know just encrypted the message (also called as ciphertext). In this situation, it is tough to find cipher key to decrypt the ciphertext into plaintext. If
cryptanalyst knows encryption algorithm, cipher text, and one or more plaintext & ciphertext
pairs formed with the secret key, then he can attack plaintext.
Attack: In this method, attackers try every
possible key on a piece of ciphertext
until they obtain an intelligible
translation of ciphertext into plaintext. In this approach, attackers must try on average half of the possible keys
to achieving success. That means if there
are N possible keys then on average attacker can discover the actual key after
N/2 tries. If the plain text converts into a digital
file and compressed, then it is tough to find the possible keys. In brute-force
approach, some knowledge about plain text
is required to list out the possible keys.