Cryptanalysis Flashcards
Brute Force
Trying every possible key to breaking a cipher. For many types of encryption, this is completely impractical because of the amount of time it would take to try every possible key.
Cryptanalysis
Using a method (other than brute force) to derive the key of a cipher. In some cases, cryptographic techniques can be used to test the efficacy of a cryptographic algorithm. Frequently used to test hash algorithms for collisions.
Frequency Analysis
The most basic tool for breaking most classical ciphers. Not effective against modern ciphers.
Kasiski
A method of attacking polyalphabetic substitution ciphers. Can be used to deduce the length of the keyword used in the polyalphabetic substitution cipher. Developed in 1863 by Friedrich.
Chosen Plaintext Attack
A method for cracking modern cryptography. The attacker obtains the ciphertexts corresponding to a set of plain texts of own choosing. Allows the attacker to attempt to derive the key. Difficult but not impossible.
Ciphertext-only and related-key Attack
A method for cracking modern cryptography. Attacker only has access to a collection of ciphertexts. Much more likely than known plain text, but also more difficult. The attack is completely successful if the corresponding plain texts can be deduced or, even better, the key. The ability to gain any information about the underlying plain text is considered a success.
Linear Cryptanalysis
Based on finding the approximations to the action of a cipher. Commonly used on block ciphers. A known plain text attack that uses a linear approximation to describe the behavior of the block cipher. Given enough pairs of plain text and corresponding ciphertext, bits of information about the key can be obtained. The more pairs of plain text and cipher text the greater chance of success.
Differential Cryptanalysis
Form of cryptanalysis applicable to symmetric key algorithms. The examination of differences in input and how that affects the resultant difference in output. Originally only worked w/ chosen plain text.
Integral Cryptanalysis
An attack that is particularly successful against block ciphers based on substitution-permutation networks. For a block size b, holds b-k bits constant and runs the other k through all 2k possibilities. For k=1, this is just deferential cryptanalysis, but with k>1 it is a new technique.
Cryptanalysis Resources
Regardless of the technique used, there is always three present:
Time - number of primitive operations which must be performed
Memory - Amount of storage required for the attack
Data - the number of plain texts and ciphertexts required.
Total Break (Cryptanalysis Success)
A cryptanalysis success where the attacker deduces the secret key.
Global Deduction (Cryptanalysis Success)
A cryptanalysis success where the attacker discovers a functionally equivalent algorithm for encryption and decryption, but without key learning.
Instance (Local) Deduction - (Cryptanalysis Success)
A cryptanalysis success where the attacker discovers additional plain texts (or ciphertexts) not previously known.
Information Deduction (Cryptanalysis Success)
A cryptanalysis success where the attacker gains some Shannon information about plain texts (or ciphertexts) not previously known.
Distinguishing Algorithm (Cryptanalysis Success)
A cryptanalysis success where the attacker can distinguish the cipher from a random permutation.
