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Encyclopedia > Message authentication code

A cryptographic message authentication code (MAC) is a short piece of information used to authenticate a message. A MAC algorithm accepts as input a secret key and an arbitrary-length message to be authenticated, and outputs a MAC (sometimes known as a tag). The MAC value protects both a message's integrity as well as its authenticity, by allowing verifiers (who also possess the secret key) to detect any changes to the message content. The German Lorenz cipher machine, used in World War II for encryption of very high-level general staff messages Cryptography (or cryptology; derived from Greek κρυπτός kryptós hidden, and the verb γράφω gráfo write or λεγειν legein to speak) is the study of message secrecy. ... This page deals with authentication in computing. ... In mathematics, computing, linguistics, and related disciplines, an algorithm is a finite list of well-defined instructions for accomplishing some task that, given an initial state, will terminate in a defined end-state. ... A key is a piece of information that controls the operation of a cryptography algorithm. ... This article is about the ethical concept. ... For other uses of the terms authentication, authentic and authenticity, see authenticity. ...


A message integrity code (MIC) is different from a MAC in that a secret key is not used in its operation. Although the terms are sometimes used interchangably, a MIC should always be encrypted during transmission if it is to be used as a reliable gauge of message integrity. On the other hand, a MAC, which uses a secret key, does not necessarily need to be encrypted to provide the same level of assurance. A given message will always produce the same MIC assuming the same algorithm is used to generate both. Conversely, the same message can only generate matching MACs if the same secret key is used with the same algorithms to generate both. MICs don't use secret keys and, when taken on their own, are therefore a much less reliable gauge of message integrity.


While MAC functions are similar to cryptographic hash functions, they possess different security requirements. To be considered secure, a MAC function must resist existential forgery under chosen-plaintext attacks. This means that even if an attacker has access to an oracle which possesses the secret key and generates MACs for messages of the attacker's choosing, he can "never" guess the MAC for any message that he has not yet asked the oracle about. (Here "never" means, "not without doing an infeasible amount of computation"). In cryptography, a cryptographic hash function is a hash function with certain additional security properties to make it suitable for use as a primitive in various information security applications, such as authentication and message integrity. ... In a digital signature system, an existential forgery is the creation (by an adversary) of any message and a valid signature for , where has not been signed in the past by the legitimate signer. ... A chosen plaintext attack is any form of cryptanalysis which presumes that the attacker has the capability to choose arbitrary plaintexts to be encrypted and obtain the corresponding ciphertexts. ...


MACs differ from digital signatures, as MAC values are both generated and verified using the same secret key. This implies that the sender and receiver of a message must agree on keys before initiating communications, as is the case with symmetric encryption. For the same reason, MACs do not provide the property of non-repudiation offered by signatures: any user who can verify a MAC is also capable of generating MACs for other messages. In contrast, a digital signature is generated using the private key of a key pair, which is asymmetric encryption. Since this private key is only accessible to its holder, a digital signature proves that a document was signed by none other than that holder. Thus, digital signatures do offer non-repudiation. A digital signature or digital signature scheme is a type of asymmetric cryptography used to simulate the security properties of a signature in digital, rather than written, form. ... A symmetric-key algorithm is an algorithm for cryptography that uses the same cryptographic key to encrypt and decrypt the message. ... Non-repudiation is the concept of ensuring that a contract, especially one agreed to via the Internet, cannot later be denied by one of the parties involved. ... PKC, see PKC (disambiguation) Public-key cryptography is a form of modern cryptography which allows users to communicate securely without previously agreeing on a shared secret key. ...


MAC algorithms can be constructed from other cryptographic primitives, such as cryptographic hash functions (as in the case of HMAC) or from block cipher algorithms (OMAC, CBC-MAC and PMAC). In cryptography, a cryptographic hash function is a hash function with certain additional security properties to make it suitable for use as a primitive in various information security applications, such as authentication and message integrity. ... A keyed-hash message authentication code, or HMAC, is a type of message authentication code (MAC) calculated using a cryptographic hash function in combination with a secret key. ... Encryption Decryption In cryptography, a block cipher is a symmetric key cipher which operates on fixed-length groups of bits, termed blocks, with an unvarying transformation. ... OMAC (One-key MAC) is a message authentication code constructed from a block cipher much like the PMAC algorithm. ... CBC-MAC stands for Cipher Block Chaining Message Authentication Code. ... PMAC, which stands for Parallelizable MAC, is a message authentication code algorithm. ...


Example

Image:MAC.gif Image File history File links macdonald college logo File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ...


See also

There are very few or no other articles that link to this one. ... The Data Authentication Algorithm (DAA) is a former U.S. government standard for producing cryptographic message authentication codes. ... The American National Standards Institute or ANSI (pronounced an-see) is a nonprofit organization that oversees the development of standards for products, services, processes and systems in the United States. ... UMAC - Wikipedia /**/ @import /skins-1. ... A keyed-hash message authentication code, or HMAC, is a type of message authentication code (MAC) calculated using a cryptographic hash function in combination with a secret key. ... CMAC (Cipher-based MAC) is a block cipher-based message authentication code algorithm, it may be used to provide assurance of the authenticity and, hence, the integrity of binary data. ... Poly1305-AES is a secure hash function written by Daniel J. Bernstein External links Poly1305-AES Categories: Cryptography stubs | Cryptographic hash functions ...

External links

  • RSA FAQ's entry on MACs
  • Ron Rivest lecture on MACs

  Results from FactBites:
 
Message authentication code - Wikipedia, the free encyclopedia (373 words)
A MAC algorithm accepts as input a secret key and an arbitrary-length message to be authenticated, and outputs a MAC (sometimes known as a tag).
MACs differ from digital signatures, as MAC values are both generated and verified using the same secret key.
This implies that the sender and receiver of a message must agree on keys before initiating communications, as is the case with symmetric encryption.
message authentication code - Article and Reference from OnPedia.com (139 words)
A MAC algorithm (sometimes termed a keyed hash function) accepts as input a secret key as well as the message, and produces a MAC (sometimes known as a tag).
The MAC protects both a message's integrity—by ensuring that a different MAC will be produced if the message has changed—as well as its authenticity—because only someone who knows the secret key could have generated a valid MAC.
MAC algorithms can be constructed from other cryptographic primitives, such as cryptographic hash functions (as in the case of HMAC) or from block cipher algorithms (OMAC and PMAC).
  More results at FactBites »

 
 

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