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Book cipher. The King James Bible, a highly available publication suitable for the book cipher. A book cipher is a cipher in which each word or letter in the plaintext of a message is replaced by some code that locates it in another text, the key . A simple version of such a cipher would use a specific book as the key, and would replace each ...
Playfair cipher. The Playfair cipher uses a 5×5 grid of letters, and encrypts a message by breaking the text into pairs of letters and swapping them according to their positions in a rectangle within that grid: "HI" becomes "BM". The Playfair cipher or Playfair square or Wheatstone–Playfair cipher is a manual symmetric encryption technique ...
In cryptanalysis, frequency analysis (also known as counting letters) is the study of the frequency of letters or groups of letters in a ciphertext. The method is used as an aid to breaking classical ciphers . Frequency analysis is based on the fact that, in any given stretch of written language, certain letters and combinations of letters ...
One-time pad. A format of one-time pad used by the U.S. National Security Agency, code named DIANA. The table on the right is an aid for converting between plaintext and ciphertext using the characters at left as the key. In cryptography, the one-time pad ( OTP) is an encryption technique that cannot be cracked, but requires the use of a single ...
Public-key cryptography. An unpredictable (typically large and random) number is used to begin generation of an acceptable pair of keys suitable for use by an asymmetric key algorithm. In an asymmetric key encryption scheme, anyone can encrypt messages using a public key, but only the holder of the paired private key can decrypt such a message.
The book used as a key to the cipher was either Commentaries on the Laws of England by William Blackstone or Nathan Bailey's Dictionary. The cipher consisted of a series of three numbers separated by periods. These numbers represented a page number of the agreed book, a line number on that page, and a word number in that line.
Block cipher. In cryptography, a block cipher is a deterministic algorithm that operates on fixed-length groups of bits, called blocks. Block ciphers are the elementary building blocks of many cryptographic protocols. They are ubiquitous in the storage and exchange of data, where such data is secured and authenticated via encryption .
A cryptographic hash function ( CHF) is a hash algorithm (a map of an arbitrary binary string to a binary string with a fixed size of bits) that has special properties desirable for a cryptographic application: [ 1] the probability of a particular. n {\displaystyle n} -bit output result ( hash value) for a random input string ("message") is.