# Cryptography

**cryptographiccryptographercryptologydecryptioncryptologistcryptologiccryptographicallycryptographersdecryptdecrypted**

Cryptography or cryptology (from "hidden, secret"; and graphein, "to write", or -logia, "study", respectively ) is the practice and study of techniques for secure communication in the presence of third parties called adversaries.wikipedia

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### Encryption

**encryptedencryptencrypting**

Cryptography prior to the modern age was effectively synonymous with encryption, the conversion of information from a readable state to apparent nonsense.

In cryptography, encryption is the process of encoding a message or information in such a way that only authorized parties can access it and those who are not authorized cannot, Encryption does not itself prevent interference, but denies the intelligible content to a would-be interceptor.

### Rotor machine

**rotor cipher machinerotorrotor cipher machines**

Since the development of rotor cipher machines in World War I and the advent of computers in World War II, the methods used to carry out cryptology have become increasingly complex and its application more widespread.

In cryptography, a rotor machine is an electro-mechanical stream cipher device used for encrypting and decrypting secret messages.

### Adversary (cryptography)

**adversaryattackeradversaries**

Cryptography or cryptology (from "hidden, secret"; and graphein, "to write", or -logia, "study", respectively ) is the practice and study of techniques for secure communication in the presence of third parties called adversaries.

In cryptography, an adversary (rarely opponent, enemy) is a malicious entity whose aim is to prevent the users of the cryptosystem from achieving their goal (primarily privacy, integrity, and availability of data).

### One-time pad

**one-time tapeone time padVernam cipher**

There exist information-theoretically secure schemes that cannot be broken even with unlimited computing power—an example is the one-time pad—but these schemes are more difficult to use in practice than the best theoretically breakable but computationally secure mechanisms.

In cryptography, the one-time pad (OTP) is an encryption technique that cannot be cracked, but requires the use of a one-time pre-shared key the same size as, or longer than, the message being sent.

### Computational hardness assumption

**computational hardness assumptionscomputational securityhard**

Modern cryptography is heavily based on mathematical theory and computer science practice; cryptographic algorithms are designed around computational hardness assumptions, making such algorithms hard to break in practice by any adversary.

Computational hardness assumptions are of particular importance in cryptography.

### Alice and Bob

**AliceEveAlice, Bob**

The cryptography literature often uses the names Alice ("A") for the sender, Bob ("B") for the intended recipient, and Eve ("eavesdropper") for the adversary.

Alice and Bob are fictional characters commonly used as placeholder names in cryptology, as well as science and engineering literature.

### Ciphertext

**Cipher textciphertextscyphertext**

Until modern times, cryptography referred almost exclusively to encryption, which is the process of converting ordinary information (called plaintext) into unintelligible form (called ciphertext).

In cryptography, ciphertext or cyphertext is the result of encryption performed on plaintext using an algorithm, called a cipher.

### Key (cryptography)

**keykeysencryption key**

The detailed operation of a cipher is controlled both by the algorithm and in each instance by a "key".

In cryptography, a key is a piece of information (a parameter) that determines the functional output of a cryptographic algorithm.

### Algorithm

**algorithmsalgorithm designcomputer algorithm**

Modern cryptography is heavily based on mathematical theory and computer science practice; cryptographic algorithms are designed around computational hardness assumptions, making such algorithms hard to break in practice by any adversary.

Arabic mathematicians such as Al-Kindi in the 9th century used cryptographic algorithms for code-breaking, based on frequency analysis.

### Plaintext

**cleartextin the clearunencrypted**

Until modern times, cryptography referred almost exclusively to encryption, which is the process of converting ordinary information (called plaintext) into unintelligible form (called ciphertext).

In cryptography, plaintext usually means unencrypted information pending input into cryptographic algorithms, usually encryption algorithms.

### Cipher

**cipherscyphercipher machine**

A cipher (or cypher) is a pair of algorithms that create the encryption and the reversing decryption.

In cryptography, a cipher (or cypher) is an algorithm for performing encryption or decryption—a series of well-defined steps that can be followed as a procedure.

### Public-key cryptography

**public keypublic key cryptographyprivate key**

There are two kinds of cryptosystems: symmetric and asymmetric.

The generation of such keys depends on cryptographic algorithms based on mathematical problems to produce one-way functions.

### Nonsense

**nonsensicalbaloneydaft stuff**

Cryptography prior to the modern age was effectively synonymous with encryption, the conversion of information from a readable state to apparent nonsense.

It is also an important field of study in cryptography regarding separating a signal from noise.

### Integer factorization

**prime factorizationfactoringfactorization**

These schemes are therefore termed computationally secure; theoretical advances, e.g., improvements in integer factorization algorithms, and faster computing technology require these solutions to be continually adapted.

The presumed difficulty of this problem is at the heart of widely used algorithms in cryptography such as RSA.

### Symmetric-key algorithm

**symmetric keysymmetric encryptionsymmetric**

There are two kinds of cryptosystems: symmetric and asymmetric.

Symmetric-key algorithms are algorithms for cryptography that use the same cryptographic keys for both encryption of plaintext and decryption of ciphertext.

### The Gold-Bug

**The Gold BugLe Scarabée d'orEdgar Alan Poe's short story**

The first use of the term cryptograph (as opposed to cryptogram) dates back to the 19th century—originating from The Gold-Bug, a novel by Edgar Allan Poe.

He took advantage of the popularity of cryptography as he was writing "The Gold-Bug", and the success of the story centers on one such cryptogram.

### Data Encryption Standard

**DESDES encryptionATSC DES**

Symmetric models include the commonly used AES (Advanced Encryption Standard) which replaced the older DES (Data Encryption Standard).

Although its short key length is of 56 bits, criticized from the beginning, makes it too insecure for most current applications, it was highly influential in the advancement of modern cryptography.

### Code (cryptography)

**codecodescodetext**

In colloquial use, the term "code" is often used to mean any method of encryption or concealment of meaning.

In cryptology, a code is a method used to encrypt a message that operates at the level of meaning; that is, words or phrases are converted into something else.

### Cryptanalysis

**cryptanalystcodebreakingcodebreaker**

Cryptanalysis is the term used for the study of methods for obtaining the meaning of encrypted information without access to the key normally required to do so; i.e., it is the study of how to crack encryption algorithms or their implementations.

Cryptanalysis is used to breach cryptographic security systems and gain access to the contents of encrypted messages, even if the cryptographic key is unknown.

### Substitution cipher

**substitutionmonoalphabetic substitution ciphersubstitution ciphers**

The main classical cipher types are transposition ciphers, which rearrange the order of letters in a message (e.g., 'hello world' becomes 'ehlol owrdl' in a trivially simple rearrangement scheme), and substitution ciphers, which systematically replace letters or groups of letters with other letters or groups of letters (e.g., 'fly at once' becomes 'gmz bu podf' by replacing each letter with the one following it in the Latin alphabet).

In cryptography, a substitution cipher is a method of encrypting by which units of plaintext are replaced with ciphertext, according to a fixed system; the "units" may be single letters (the most common), pairs of letters, triplets of letters, mixtures of the above, and so forth.

### Military communications

**Signalscommunicationssignal**

Applications of cryptography include electronic commerce, chip-based payment cards, digital currencies, computer passwords, and military communications.

The first military communications involved the use of runners or the sending and receiving of simple signals (sometimes encoded to be unrecognizable).

### Steganography

**steganographicsteganographicallysecret writing**

advises that steganography is sometimes included in cryptology.

The advantage of steganography over cryptography alone is that the intended secret message does not attract attention to itself as an object of scrutiny.

### Secure multi-party computation

**secure multiparty computationsecure computationVirtual Party Protocol**

In recent decades, the field has expanded beyond confidentiality concerns to include techniques for message integrity checking, sender/receiver identity authentication, digital signatures, interactive proofs and secure computation, among others.

Secure multi-party computation (also known as secure computation, multi-party computation (MPC), or privacy-preserving computation) is a subfield of cryptography with the goal of creating methods for parties to jointly compute a function over their inputs while keeping those inputs private.

### Transposition cipher

**transpositionPermutation cipherDouble Transposition**

The main classical cipher types are transposition ciphers, which rearrange the order of letters in a message (e.g., 'hello world' becomes 'ehlol owrdl' in a trivially simple rearrangement scheme), and substitution ciphers, which systematically replace letters or groups of letters with other letters or groups of letters (e.g., 'fly at once' becomes 'gmz bu podf' by replacing each letter with the one following it in the Latin alphabet).

In cryptography, a transposition cipher is a method of encryption by which the positions held by units of plaintext (which are commonly characters or groups of characters) are shifted according to a regular system, so that the ciphertext constitutes a permutation of the plaintext.

### Caesar cipher

**CaesarCaesar shift cipherCaesar's cipher**

An early substitution cipher was the Caesar cipher, in which each letter in the plaintext was replaced by a letter some fixed number of positions further down the alphabet.

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.