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Partial-matching Meet-in-the-middle Attack
Partial-matching is a technique that can be used with a MITM attack. Partial-matching is where the intermediate values of the MITM attack, i and j, computed from the plaintext and ciphertext, are matched on only a few select bits, instead of on the complete state. Uses A limitation with MITM attacks is the amount of intermediate values that needs to be stored. In order to compare the intermediate values i and j, all i's need to be computed and stored first, before each computed j can be compared against them. If the two subciphers identified by the MITM attack both has a sufficiently large subkey, then an unfeasible amount of intermediate values need to be stored. While there are techniques such as cycle detection algorithms that allows one to perform a MITM attack without storing either all values of i or j, these techniques requires that the subciphers of the MITM attack are symmetric. Thus it is a solution that allows one to perform a MITM attack in a situation, where the su ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Meet-in-the-middle Attack
The meet-in-the-middle attack (MITM), a known-plaintext attack, is a generic space–time tradeoff cryptographic attack against encryption schemes that rely on performing multiple encryption operations in sequence. The MITM attack is the primary reason why Double DES is not used and why a Triple DES key (168-bit) can be brute-forced by an attacker with 256 space and 2112 operations. Description When trying to improve the security of a block cipher, a tempting idea is to encrypt the data several times using multiple keys. One might think this doubles or even ''n''-tuples the security of the multiple-encryption scheme, depending on the number of times the data is encrypted, because an exhaustive search on all possible combinations of keys (simple brute force) would take 2''n''·''k'' attempts if the data is encrypted with ''k''-bit keys ''n'' times. The MITM attack is a generic attack which weakens the security benefits of using multiple encryptions by storing intermediate value ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cycle Detection
In computer science, cycle detection or cycle finding is the algorithmic problem of finding a cycle in a sequence of iterated function values. For any function that maps a finite set to itself, and any initial value in , the sequence of iterated function values : x_0,\ x_1=f(x_0),\ x_2=f(x_1),\ \dots,\ x_i=f(x_),\ \dots must eventually use the same value twice: there must be some pair of distinct indices and such that . Once this happens, the sequence must continue periodically, by repeating the same sequence of values from to . Cycle detection is the problem of finding and , given and . Several algorithms are known for finding cycles quickly and with little memory. Robert W. Floyd's tortoise and hare algorithm moves two pointers at different speeds through the sequence of values until they both point to equal values. Alternatively, Brent's algorithm is based on the idea of exponential search. Both Floyd's and Brent's algorithms use only a constant number of memor ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
