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Hill's cipher machine, from figure 4 of the patent. In classical cryptography, the Hill cipher is a polygraphic substitution cipher based on linear algebra.Invented by Lester S. Hill in 1929, it was the first polygraphic cipher in which it was practical (though barely) to operate on more than three symbols at once.
Classical ciphers are typically vulnerable to known-plaintext attack. For example, a Caesar cipher can be solved using a single letter of corresponding plaintext and ciphertext to decrypt entirely. A general monoalphabetic substitution cipher needs several character pairs and some guessing if there are fewer than 26 distinct pairs.
The goal of the attack is to gain information that reduces the security of the encryption scheme. [ 2 ] Modern ciphers aim to provide semantic security, also known as ciphertext indistinguishability under chosen-plaintext attack , and they are therefore, by design, generally immune to chosen-plaintext attacks if correctly implemented.
For example, the El Gamal cryptosystem is semantically secure under chosen-plaintext attack, but this semantic security can be trivially defeated under a chosen-ciphertext attack. Early versions of RSA padding used in the SSL protocol were vulnerable to a sophisticated adaptive chosen-ciphertext attack which revealed SSL session keys.
In cryptography, a substitution cipher is a method of encrypting in which units of plaintext are replaced with the ciphertext, in a defined manner, with the help of a key; the "units" may be single letters (the most common), pairs of letters, triplets of letters, mixtures of the above, and so forth.
All too common current examples are commercial security products that derive keys for otherwise impregnable ciphers like AES from a user-selected password. Since users rarely employ passwords with anything close to the entropy of the cipher's key space, such systems are often quite easy to break in practice using only ciphertext.
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Cipher Security claim Best attack Publish date Comment AES128: 2 128: 2 126.1 time, 2 88 data, 2 8 memory : 2011-08-17 Independent biclique attack. [1] AES192 2 192: 2 189.7 time, 2 80 data, 2 8 memory : AES256 2 256: 2 254.4 time, 2 40 data, 2 8 memory : Blowfish: Up to 2 448: 4 of 16 rounds; 64-bit block is vulnerable to SWEET32 attack. 2016 ...