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However key lengths are not directly comparable between symmetric and asymmetric systems. [2] Furthermore, the details of implementation can render the system vulnerable. For example, in 2008 it was revealed that a number of hard drives sold with built-in "128-bit AES encryption" were actually using a simple and easily defeated " XOR " scheme.
In cryptography, a Caesar cipher, also known as Caesar's cipher, the shift cipher, Caesar's code, or Caesar shift, is one of the simplest and most widely known encryption techniques. It is a type of substitution cipher in which each letter in the plaintext is replaced by a letter some fixed number of positions down the alphabet .
Edgar Allan Poe, author of the book, A Few Words on Secret Writing, an essay on cryptanalysis, and The Gold Bug, a short story featuring the use of letter frequencies in the solution of a cryptogram. Johannes Trithemius, mystic and first to describe tableaux (tables) for use in polyalphabetic substitution.
Modern Cryptography Theory and Practice ISBN 0-13-066943-1. An up-to-date book on cryptography. Touches on provable security, and written with students and practitioners in mind. Mel, H.X., and Baker, Doris (2001). Cryptography Decrypted, Addison Wesley ISBN 0-201-61647-5. This technical overview of basic cryptographic components (including ...
asymmetric key algorithms (Public-key cryptography), where two different keys are used for encryption and decryption. In a symmetric key algorithm (e.g., DES and AES), the sender and receiver must have a shared key set up in advance and kept secret from all other parties; the sender uses this key for encryption, and the receiver uses the same ...
Challenge-response authentication can help solve the problem of exchanging session keys for encryption. Using a key derivation function, the challenge value and the secret may be combined to generate an unpredictable encryption key for the session. This is particularly effective against a man-in-the-middle attack, because the attacker will not ...
Kerckhoffs viewed cryptography as a rival to, and a better alternative than, steganographic encoding, which was common in the nineteenth century for hiding the meaning of military messages. One problem with encoding schemes is that they rely on humanly-held secrets such as "dictionaries" which disclose for example, the secret meaning of words.
The most obvious application of a public key encryption system is for encrypting communication to provide confidentiality – a message that a sender encrypts using the recipient's public key, which can be decrypted only by the recipient's paired private key. Another application in public key cryptography is the digital signature.