Cryptanalysis is a study of principles or method of decrypting ciphertext# without knowing the key. People who study or practise cryptanalysis are known as cryptanalyst, intruder, or attacker. The results of a Cryptanalysis doesn’t necessary bad, as they are useful feedbacks to the cryptographers to improve their #algorithm.
There are two general approaches on how to decrypt the ciphertext without the key:
Symmetric Cryptography, or Private-Key Cryptography is a #Cryptographic system that uses the same key for encryption and decryption. However, you can already imagine the security risk of sharing the same secret over a network, requiring a secure channel (usually via IPsec#). If the key get compromised#, it means the need to generate a new key and distribute# it again. It also requires a strong encryption #algorithm for the intruder to not be able to guess the secret key easily. That being said, it is quite fast when comparing to Asymmetric Cryptography.
Simple Secret Key Distribution, invented by Merkle in 1979, is an #Asymmetric Cryptography used to #distribute private key. There is a security risk where the intruder can intercept and impersonate both halves of the protocol. The process works as follows:
Simple Authentication Dialogue is a simple scheme that authenticates# users with username and password. It comes with a problem: If the password is transmitted in plaintext, then the user is vulnerable to eavesdropping#. Furthermore, it could prompt too many times for the user to enter their password as their sessions come to an end which could be one of the information the Cryptanalyst can utilise.
A Cryptanalysis could be done to this cipher by simply analysing the number of characters used in the ciphertext and guess the number of rows it’s using.
A Cryptanalysis could be done to this cipher by simply analysing the number of characters used in the ciphertext and guess the number of rows it’s using.
MITM is a #Cryptanalytic Attack where the Cryptanalyst found a way to be in between two parties in a communication channel. It is exceptionally dangerous to encryption scheme that involves key exchange such as Symmetric Cryptography# and Asymmetric Cryptography#. It is form of #Interception.
Using the method 2 and 3, session key and master key are necessary to verify and secure the Key Distribution from possible intruder. Session key is a temporary key used for encryption of data between users. It will be discarded once the session is over, hence the name. Master key is a key that is used to encrypt the session key, which is shared by the users and Key Distribution Center (KDC)#.
Note: The lifetime of the session key should not be too long or too short. If the lifetime is too long, it is vulnerable to Replay Attack# which will be used by the intruder to access the services. The lifetime should not be too as to avoid asking password too frequently.
Differential Cryptanalysis Attack is a #chosen plaintext attack on block ciphers which the Cryptanalyst analyses the relationship of pairs of plaintexts to the targeted algorithm.
Cryptology is a field of study that includes Cryptography# and Cryptanalysis#.
Cryptanalytic Attack is performed based on the nature of the cryptographic #algorithm with the complement from the general characteristic of the plaintext. It is essentially finding a relationship between the plaintext and the ciphertext. Some #Cryptanalysts would use the sample plaintext-ciphertext pairs in aid on cracking the algorithm down. The purpose of the Cryptanalytic Attack is to find the relationship between the information that the cryptanalyst has obtained.
However, CBC is a rather slow algorithm compare to Electronic Codebook (ECB) since the block can’t be computed in parallel. In terms of security, the attacker could utilise the CBC nature of using ciphertext as the input for the XOR of the next plaintext, and obtain some information about the next ciphertext.
Brute Force Attack, aka Exhaustive Key Search, is a #Cryptanalysis technique that attempts to obtain an intelligible plaintext by trying every possible key on a piece of ciphertext. On average, \(\frac{N}{2}\) number of keys must be tried before a success, where \(N\) annotates the total number of possible keys. Therefore, we know that the time used by Brute Force Attack is proportional to the key size: the larger the key size, the longer the time taken to crack the algorithm.
If a #Cryptanalysis could crack an encryption scheme with an attempts less than of the Brute Force Attack, then it is considered to be a Cryptanalytic Attack on the scheme.
A Cryptanalysis could be done to this cipher by simply analysing the number of characters used in the ciphertext and guess the number of columns it’s using.