A key measure in information theory is "entropy". Entropy quantifies the amount of uncertainty involved in the value of a random variable or the outcome of a random process. For example, identifying the outcome of a fair coin flip (with two equally likely outcomes) provides less information (lower entropy) than specifying the outcome from a roll of a dice (with six equally likely outcomes). Some other important measures in information theory are mutual information, channel capacity, error exponents, and relative entropy.
Block cipher
In cryptography, a block cipher is a symmetric key cipher which operates on a groups of bits of fixed length, called "blocks", using an exact transformation. During encryption, a block cipher algorithm might take (for example) a 128-bit block of plaintext as input, and output a corresponding 128-bit block of ciphertext. The exact transformation is controlled using a second input — the secret key. Decryption is similar: the decryption algorithm takes, in this example, a 128-bit block of ciphertext together with the secret key, and output the original 128-bit block of plaintext.
One of the early block cipher designs was the Data Encryption Standard (DES), developed at IBM and published as a standard in 1977. A successor to DES, the Advanced Encryption Standard (AES); also using block cipher, was adopted in 2001.
Authentication
Authentication (pronounced "aw-then-ti-keyt") (from Greek "αυθεντικός;" real or genuine, from "authentes;" author) is the actions taken to establish or verify something (or someone) as "authentic". It is the method of verifying claims made by someone about the thing. This might involve confirming the identity of a person, the origins of an object (or something), or to make sure that a computer program (or user) is a trusted one. People are usually authenticated by something they know (password), something they have (key), or something they are (biometrics).
DES-X
In cryptography, DES-X (or DESX) is an alternative to the DES (Data Encryption Standard) block cipher designed to increase the complexity of a brute force attack using a technique called "key whitening". As DES suffers from brute force attack DES-X was a trial to overcome such drawbacks.
Hostname
A hostname (also known as a sitename) is the unique name by which a network device (which may be a computer, file server, network storage device, copier, cable modem, etc.) is defined and known on a network. The hostname is used to identify a particular host in various electronic communication networks such as the World Wide Web, e-mail or Usenet.
On the Internet, the terms "hostname" and "domain name" are often misused interchangeably, but there are small technical differences between them.
National Institute of Standards and Technology
The National Institute of Standards and Technology (NIST), known between 1901 and 1988 as the National Bureau of Standards (NBS), is a measurement standards laboratory which is a non-regulatory (non-controlled) agency of the United States Department of Commerce. The institute's mission is to promote U.S. innovation and industrial competitiveness by advancing measurement science, standards, and Technology in ways that enhance economic security and improve quality of life.
Key size
In cryptography, key size or key length is the size (measured in bits or bytes) of the key used in a cryptographic algorithm (such as a cipher). Typical key sizes in modern symmetric ciphers are 128, 192, and 256 bits. Older symmetric ciphers used only 40, 56, or 64 bits, which can be broken by brute force. 128 bits is considered secure against brute-force by traditional computers, but not quantum computers. 192 and 256 bit keys are considered quantum-safe, and AES keys of these lengths are approved for protecting top secret information. Asymmetric (public key) ciphers such as RSA need a much longer key to be secure. RSA keys are typically at least 2048 bits. A large key size alone does not necessarily mean a cipher is secure - there are many insecure ciphers which have a large key size but have other design flaws that allow them to be broken.
Kandinsky
Wassily Kandinsky ( – 13 December 1944) was a Russian painter, printmaker and art theorist.
He was one of the most important 20th-century artists. He was a major figure in modern art and painted some of the first modern abstract works. His art changed several times during his life. It was fauvist, abstract, expressionist and constructivist in turn.
Born in Moscow, Kandinsky spent his childhood in Odessa. He enrolled at the University of Moscow and chose to study law and economics. Quite successful in his profession—he was offered a professorship (chair of Roman Law) at the University of Dorpat—he started painting studies (life-drawing, sketching and anatomy) at the age of 30.
In 1896 he settled in Munich and studied first in a private school, then at the Academy of Fine Arts, Munich. He went back to Moscow in 1914 after World War I started. He was unsympathetic to the official theories on art in Moscow and returned to Germany in 1921. There he taught at the Bauhaus school of art and architecture from 1922 until the Nazis closed it in 1933. He then moved to France where he lived the rest of his life, and became a French citizen in 1939. He died at Neuilly-sur-Seine in 1944.
Later in life he would recall being fascinated and stimulated by colour as a child. His fascination with colour symbolism and psychology continued as he grew. In 1889, he was part of an ethnographic research group which travelled to the Vologda region north of Moscow. In "Looks on the Past", he tells how the houses and churches were decorated with such shimmering colours that, on entering them, he felt he was moving into a painting. This experience, and his study of the region's folk art (particularly the use of bright colours on a dark background), can be seen in much of his early work.
He was interested in geometry in art and philosophy. The creative aspect of the form is expressed by a descending series of circles, triangles and squares.
Public-key cryptography
Public-key cryptography, also called asymmetric cryptography, is a communication where people exchange messages that can only be read by one another.
In public key cryptography, each user has a pair of cryptographic keys:
The private key is kept secret, while the public key may be widely distributed and used by other users.
Incoming messages are encrypted with the "recipient's public key" and can only be decrypted with their corresponding private key. The keys are related mathematically, but the user's private key cannot be easily got from the widely used public key. The most usual problem with this method arises when private key is accidentally leaked.
The two main branches of public key cryptography are:
They are often used together on the same message.
John Ashcroft
John David Ashcroft (born May 9, 1942) is an American consultant, lobbyist and politician. He was the 79th United States Attorney General. He served during the first term of President George W. Bush from 2001 until 2005. Ashcroft was previously the Governor of Missouri (1985–1993) and a U.S. Senator from Missouri (1995–2001). Ashcroft was born in Chicago, Illinois.
Muslim conquests
The first Arab Muslim conquests (632–732), (, Fatah, literally "opening",) also referred to as the Islamic conquests or Arab conquests, began after the death of the Islamic prophet Muhammad. He established a new unified political polity in the Arabian peninsula which under the following Rashidun and Umayyad Caliphates saw a century of rapid expansion of Arab power well beyond the Arabian peninsula in the form of a vast Muslim Arab Empire with an area of influence that stretched from northwest India, across Central Asia, the Middle East, North Africa, southern Italy, and the Iberian Peninsula, to the Pyrenees.