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Ciphertext-only
In cryptography, a ciphertext-only attack (COA) or known ciphertext attack is an attack model for cryptanalysis where the attacker is assumed to have access only to a set of ciphertexts. While the attacker has no channel providing access to the plaintext prior to encryption, in all practical ciphertext-only attacks, the attacker still has some knowledge of the plaintext. For instance, the attacker might know the language in which the plaintext is written or the expected statistical distribution of characters in the plaintext. Standard protocol data and messages are commonly part of the plaintext in many deployed systems and can usually be guessed or known efficiently as part of a ciphertext-only attack on these systems. Attack The attack is completely successful if the corresponding plaintexts can be deduced, or even better, the key. The ability to obtain any information at all about the underlying plaintext beyond what was pre-known to the attacker is still considered a succes ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cryptanalysis
Cryptanalysis (from the Greek ''kryptós'', "hidden", and ''analýein'', "to analyze") refers to the process of analyzing information systems in order to understand hidden aspects of the systems. Cryptanalysis is used to breach cryptographic security systems and gain access to the contents of encrypted messages, even if the cryptographic key is unknown. In addition to mathematical analysis of cryptographic algorithms, cryptanalysis includes the study of side-channel attacks that do not target weaknesses in the cryptographic algorithms themselves, but instead exploit weaknesses in their implementation. Even though the goal has been the same, the methods and techniques of cryptanalysis have changed drastically through the history of cryptography, adapting to increasing cryptographic complexity, ranging from the pen-and-paper methods of the past, through machines like the British Bombes and Colossus computers at Bletchley Park in World War II, to the mathematically advanced comput ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ciphertext
In cryptography, ciphertext or cyphertext is the result of encryption performed on plaintext using an algorithm, called a cipher. Ciphertext is also known as encrypted or encoded information because it contains a form of the original plaintext that is unreadable by a human or computer without the proper cipher to decrypt it. This process prevents the loss of sensitive information via hacking. Decryption, the inverse of encryption, is the process of turning ciphertext into readable plaintext. Ciphertext is not to be confused with codetext because the latter is a result of a code, not a cipher. Conceptual underpinnings Let m\! be the plaintext message that Alice wants to secretly transmit to Bob and let E_k\! be the encryption cipher, where _k\! is a cryptographic key. Alice must first transform the plaintext into ciphertext, c\!, in order to securely send the message to Bob, as follows: : c = E_k(m). \! In a symmetric-key system, Bob knows Alice's encryption key. Once the m ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Attack Model
In cryptanalysis, attack models or attack types are a classification of cryptographic attacks specifying the kind of access a Cryptanalysis, cryptanalyst has to a system under attack when attempting to "break" an Encryption, encrypted message (also known as ''ciphertext'') generated by the system. The greater the access the cryptanalyst has to the system, the more useful information they can get to utilize for breaking the cypher. In cryptography, a sending party uses a cipher to encryption, encrypt (transform) a secret ''plaintext'' into a ''ciphertext'', which is sent over an insecure communication channel to the receiving party. The receiving party uses an inverse cipher to decryption, decrypt the ciphertext to obtain the plaintext. A secret knowledge is required to apply the inverse cipher to the ciphertext. This secret knowledge is usually a short number or string called a ''cryptographic key, key''. In a cryptographic attack a third party cryptanalyst analyzes the ciphertex ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cryptanalysis Of The Enigma
Cryptanalysis of the Enigma ciphering system enabled the western Allies in World War II to read substantial amounts of Morse-coded radio communications of the Axis powers that had been enciphered using Enigma machines. This yielded military intelligence which, along with that from other decrypted Axis radio and teleprinter transmissions, was given the codename '' Ultra''. The Enigma machines were a family of portable cipher machines with rotor scramblers. Good operating procedures, properly enforced, would have made the plugboard Enigma machine unbreakable. However, most of the German military forces, secret services, and civilian agencies that used Enigma employed poor operating procedures, and it was these poor procedures that allowed the Enigma machines to be reverse-engineered and the ciphers to be read. The German plugboard-equipped Enigma became Nazi Germany's principal crypto-system. In December 1932 it was "broken" by mathematician Marian Rejewski at the Polish G ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Akelarre (cipher)
Akelarre is a block cipher proposed in 1996, combining the basic design of IDEA with ideas from RC5. It was shown to be susceptible to a ciphertext-only attack in 1997. Akelarre is a 128-bit block cipher with a variable key-length which must be some multiple of 64 bits. The number of rounds is variable, but four are suggested. The round function of Akelarre is similar to IDEA in structure. After the successful cryptanalysis of Akelarre, its designers responded with an updated variant called Ake98. This cipher differs from the original Akelarre in the new ''AR-box'' (addition–rotation box), the swapping of words at the end of a round, and the addition of subkeys at the beginning of each round. In 2004, Jorge Nakahara, Jr. and Daniel Santana de Freitas found large classes of weak key In cryptography, a weak key is a key, which, used with a specific cipher, makes the cipher behave in some undesirable way. Weak keys usually represent a very small fraction of the overall keys ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Data Encryption Standard
The Data Encryption Standard (DES ) is a symmetric-key algorithm for the encryption of digital data. Although its short key length of 56 bits makes it too insecure for modern applications, it has been highly influential in the advancement of cryptography. Developed in the early 1970s at IBM and based on an earlier design by Horst Feistel, the algorithm was submitted to the National Bureau of Standards (NBS) following the agency's invitation to propose a candidate for the protection of sensitive, unclassified electronic government data. In 1976, after consultation with the National Security Agency (NSA), the NBS selected a slightly modified version (strengthened against differential cryptanalysis, but weakened against brute-force attacks), which was published as an official Federal Information Processing Standard (FIPS) for the United States in 1977. The publication of an NSA-approved encryption standard led to its quick international adoption and widespread academic scrutiny. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Unicity Distance
In cryptography, unicity distance is the length of an original ciphertext needed to break the cipher by reducing the number of possible spurious keys to zero in a brute force attack. That is, after trying every possible key, there should be just one decipherment that makes sense, i.e. expected amount of ciphertext needed to determine the key completely, assuming the underlying message has redundancy. Claude Shannon defined the unicity distance in his 1949 paper " Communication Theory of Secrecy Systems". Consider an attack on the ciphertext string "WNAIW" encrypted using a Vigenère cipher with a five letter key. Conceivably, this string could be deciphered into any other string—RIVER and WATER are both possibilities for certain keys. This is a general rule of cryptanalysis: with no additional information it is impossible to decode this message. Of course, even in this case, only a certain number of five letter keys will result in English words. Trying all possible keys we ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Brute Force Attack
In cryptography, a brute-force attack consists of an attacker submitting many passwords or passphrases with the hope of eventually guessing correctly. The attacker systematically checks all possible passwords and passphrases until the correct one is found. Alternatively, the attacker can attempt to guess the key which is typically created from the password using a key derivation function. This is known as an exhaustive key search. A brute-force attack is a cryptanalytic attack that can, in theory, be used to attempt to decrypt any encrypted data (except for data encrypted in an information-theoretically secure manner). Such an attack might be used when it is not possible to take advantage of other weaknesses in an encryption system (if any exist) that would make the task easier. When password-guessing, this method is very fast when used to check all short passwords, but for longer passwords other methods such as the dictionary attack are used because a brute-force search ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Point-to-point Tunneling Protocol
The Point-to-Point Tunneling Protocol (PPTP) is an obsolete method for implementing virtual private networks. PPTP has many well known security issues. PPTP uses a TCP control channel and a Generic Routing Encapsulation tunnel to encapsulate PPP packets. Many modern VPNs use various forms of UDP for this same functionality. The PPTP specification does not describe encryption or authentication features and relies on the Point-to-Point Protocol being tunneled to implement any and all security functionalities. The PPTP implementation that ships with the Microsoft Windows product families implements various levels of authentication and encryption natively as standard features of the Windows PPTP stack. The intended use of this protocol is to provide security levels and remote access levels comparable with typical VPN products. History A specification for PPTP was published in July 1999 as RFC 2637 and was developed by a vendor consortium formed by Microsoft, Ascend Communicat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
A5/2
A5/2 is a stream cipher used to provide voice privacy in the GSM cellular telephone protocol. It was designed in 1992-1993 (finished March 1993) as a replacement for the relatively stronger (but still weak) A5/1, to allow the GSM standard to be exported to countries "with restrictions on the import of products with cryptographic security features". The cipher is based on a combination of four linear-feedback shift registers with irregular clocking and a non-linear combiner. In 1999, Ian Goldberg and David A. Wagner cryptanalyzed A5/2 in the same month it was reverse engineered, and showed that it was extremely weak – so much so that low end equipment can probably break it in real time. In 2003, Elad Barkan, Eli Biham and Nathan Keller presented a ciphertext-only attack based on the error correcting codes used in GSM communication. They also demonstrated a vulnerability in the GSM protocols that allows a man-in-the-middle attack to work whenever the mobile phone supports ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
A5/1
A5/1 is a stream cipher used to provide over-the-air communication privacy in the GSM cellular telephone standard. It is one of several implementations of the A5 security protocol. It was initially kept secret, but became public knowledge through leaks and reverse engineering. A number of serious weaknesses in the cipher have been identified. History and usage A5/1 is used in Europe and the United States. A5/2 was a deliberate weakening of the algorithm for certain export regions. A5/1 was developed in 1987, when GSM was not yet considered for use outside Europe, and A5/2 was developed in 1989. Though both were initially kept secret, the general design was leaked in 1994 and the algorithms were entirely reverse engineered in 1999 by Marc Briceno from a GSM telephone. In 2000, around 130 million GSM customers relied on A5/1 to protect the confidentiality of their voice communications. Security researcher Ross Anderson reported in 1994 that "there was a terrific row between the NAT ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Advanced Encryption Standard
The Advanced Encryption Standard (AES), also known by its original name Rijndael (), is a specification for the encryption of electronic data established by the U.S. National Institute of Standards and Technology (NIST) in 2001. AES is a variant of the Rijndael block cipher developed by two Belgian cryptographers, Joan Daemen and Vincent Rijmen, who submitted a proposal to NIST during the AES selection process. Rijndael is a family of ciphers with different key and block sizes. For AES, NIST selected three members of the Rijndael family, each with a block size of 128 bits, but three different key lengths: 128, 192 and 256 bits. AES has been adopted by the U.S. government. It supersedes the Data Encryption Standard (DES), which was published in 1977. The algorithm described by AES is a symmetric-key algorithm, meaning the same key is used for both encrypting and decrypting the data. In the United States, AES was announced by the NIST as U.S. FIPS PUB 197 (FIPS 197) on Novemb ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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