The affine cipher is a type of monoalphabetic substitution cipher, wherein each letter in an alphabet is mapped to its numeric equivalent, encrypted using a simple mathematical function, and converted back to a letter. The formula used means that each letter encrypts to one other letter, and back again, meaning the cipher is essentially a standard substitution cipher with a rule governing which letter goes to which. As such, it has the weaknesses of all substitution ciphers. Each letter is enciphered with the function , where is the magnitude of the shift.
In the affine cipher the letters of an alphabet of size are first mapped to the integers in the range . It then uses modular arithmetic to transform the integer that each plaintext letter corresponds to into another integer that correspond to a ciphertext letter. The encryption function for a single letter is
Post-quantum cryptography refers to research on cryptographic primitives (usually public-key cryptosystems) that are not efficiently breakable using quantum computers more than classical computer architectures. This term came about because most currently popular public-key cryptosystems rely on the integer factorization problem or discrete logarithm problem, both of which would be easily solvable on large enough quantum computers using Shor's algorithm. Even though current publicly known experimental quantum computing is nowhere near powerful enough to attack real cryptosystems, many cryptographers are researching new algorithms, in case quantum computing becomes a threat in the future. This work is popularized by the PQCrypto conference series since 2006.
In contrast, most current symmetric cryptographic systems (symmetric ciphers and hash functions) are secure from quantum computers. The quantum Grover's algorithm can speed up attacks against symmetric ciphers, but this can be counteracted by increasing key size. Thus post-quantum cryptography does not focus on symmetric algorithms.
A keyword cipher is a form of monoalphabetic substitution. A keyword is used as the key, and it determines the letter matchings of the cipher alphabet to the plain alphabet. Repeats of letters in the word are removed, then the cipher alphabet is generated with the keyword matching to A,B,C etc. until the keyword is used up, whereupon the rest of the ciphertext letters are used in alphabetical order, excluding those already used in the key Worked Example.
With KRYPTOS as the keyword, all As become Ks, all Bs become Rs and so on. Encrypting the message "knowledge is power" using the keyword "kryptos":
In journalism, a human interest story is a feature story that discusses a person or people in an emotional way. It presents people and their problems, concerns, or achievements in a way that brings about interest, sympathy or motivation in the reader or viewer.
Human interest stories may be "the story behind the story" about an event, organization, or otherwise faceless historical happening, such as about the life of an individual soldier during wartime, an interview with a survivor of a natural disaster, a random act of kindness or profile of someone known for a career achievement.