Constructing macs mac from hash functions macs are keyed hash functions, so it is natural to use hash functions. Message authentication codes macs ece597697 koren part. It is a merkledamgard construction with the compression function built on multivariate hash functions. Hash functions were not designed for message authentication one difficulty, in particular, is that they are keyless special care must be taken when using hash functions for macs, as you are using them in a way they were not designed for macing with cryptographic hash functions. Hash functions are extremely useful and appear in almost all information security applications. Certain obfuscation schemes rely on provablysecure hash functions. Is the security of mac function is based on hash function.
Just as with symmetric and publickey encryption, we can group attacks on hash functions and macs into two. In addition to using hash functions for implementing mac, hash functions can be used to achieve message authentication and integrity goals without the use of symmetric encryption. Oneway hash function an overview sciencedirect topics. Md5 and hmac are in the former camp functions algorithms. Section 6 studies the security of macs built on multivariate hash functions, eventually we give the conclusion in section 7. A hash function provides encryption using an algorithm and no key. Ease of computation hash functions security requirements 1. This replaceability property is fundamental given the limited con. Collision resistant hash functions and macs integrity vs authentication message integrity is the property whereby data has not been altered in an unauthorized manner since the time it was created, transmitted, or stored by an authorized source message origin authentication is a type of authentication whereby a party is corroborated. Chapter 12 message cryptography and authentication codes. We then make a list of operations which, when composed with an almostuniversal hash function, yield a secure mac. For a word size w between 164 bits, the hash provides a security claim of 2 9. A message authentication code mac is a set of functions mackx.
A cryptographic hash function h takes as input a message of arbitrary. Automated security proofs for almostuniversal hash for mac. A cryptographic hash function is a completely public, deterministic hash function which everybody can compute over arbitrary inputs. Cryptographic hash functions a carleton university. Thus, these iterated hash functions and most hash functions in the real world are of this type require that the input length is a multiple of a certain integer called the block size of the hash function.
The key thing youre missing here is that collision resistant hash functions crhfs, what we normally call just crypto hashes and message authentication codes macs have substantially different security goals. For establishing mac process, the sender and receiver share a symmetric key k. Chapter 12 message cryptography and authentication. Essentially, a mac is an encrypted checksum generated on the underlying message that is sent along with a message to ensure message. Automated security proofs for almostuniversal hash for. The security requirements for macs are only people having the shared key should be able to produce macs or verify macs. It discusses the main requirements for these cryptographic primitives, motivates these constructions, and presents the state of the art of both attacks and security proofs. Message authentication code mac mac algorithm is a symmetric key cryptographic technique to provide message authentication. Cryptographic hash functions have many information security applications, notably in digital signatures, message authentication codes macs, and other forms of authentication. Foreword this is a set of lecture notes on cryptography compiled for 6. Can use cryptographic hash functions called hmacs can use block cipher algorithms can use universal hashing hash value calculated using a randomlychosen hashing algorithm from a family of hash algorithms lower expected number of collisions. Web security starting mid next week 42419 cse 484 cse m 584 spring 2019 2.
Most hash functions are built on an ad hoc basis, where the bits of the message are nicely mixed to produce the hash. Oneway in the name refers to the property of such functions. Security of macs cryptanalytic attacks exploit structure like block ciphers want brute force attacks to be the best alternative more variety of macs so harder to generalize about cryptanalysis keyed hash functions as macs want a mac based on a hash function because hash functions are generally faster. The input to the hash function is of arbitrary length but output is always of fixed length. Realworld hash functions the three most widely employed hash functions used to be md5, ripemd160 and sha1. Sha1, sha2 message authentication codes mac provides. In this paper, we bring out the importance of hash functions, its various structures, design techniques, attacks. We also study the security of message authentication codes hmac and nmac built on multivariate hash functions, and demonstrate that families of lowdegree functions over gf2 are neither pseudo. Cryptographic hash functions have many informationsecurity applications, notably in digital signatures, message authentication codes macs, and other forms of authentication. It takes as input a sequence of bits any sequence of bits. Hash functions and macs in general one expects that for any y. The main difference is hash functions dont use a secret key. In this paper, we investigate a family of universal hash functions that has been appeared repeatedly in the literature and provide a detailed algebraic analysis for the security of. Security proofs for the md6 hash function mode of operation.
Stallings, cryptography and networksecurity, chapter 11 cryptographic hash functions appendix 11a mathematical basis of birthday attack. Cryptographic hash functions are used to achieve a number of security objectives. Cryptographic hash function has all the characteristics of a hash function output hash value meets tests for pseudorandomness relies on confusion and diffusion principles to meet even distribution requirement optionally, a key is used, such as in a desbased hash function. Attacker cant easily find two messages that hash to the same value. Hashfunctions map strings of bits of variable but usually upper bounded length to fixedlength strings of bits, using a specified algorithm.
Cryptanalysts consider a primitive broken if its security is shown to be less than ideal, even though it may still. Cryptographic hash functions and macs solved exercises for. Hashfunctions map strings of bits of variable but usually upper bounded length to fixedlength strings of bits, using a. This paper gives a survey of mac algorithms and hash functions. Stallings, cryptography and networksecurity, chapter 11 cryptographic hash functions appendix 11a mathematical basis of birthday attack chapter 12 message authentication codes required reading recommended reading sha3 competition 20072012. We say that a hash function has ideal security if the best attacks known against it are generic. What id advice is to think very carefully about which cryptographic terms refer to functions, algorithms or implementations vs. Hash functions and mac algorithms based on block ciphers. This work presents proofs of security for the mode of operation of the md6 cryptographic hash function 32 a candidate for the sha3 competition which di. They are called oneway hash functions because there is no way to reverse the encryption. Difference between macs and cryptographic hash functions mac must be resistant to existential forgery under. Hence, all the above problems will have many solutions. It describes the main properties, summarizes the most important constructions and reports on their security.
Macs and hash functions spring 2019 franziska franzi roesner. The md5 messagedigest algorithm is a widely used cryptographic hash function producing a 128bit 16byte hash. Figure a, b, c and d illustrates a variety of ways in which a hash code can be used to provide message authentication, as follows. The most popular in this genre is the cbc mac, analyzed.
Cryptography and chapter 11 cryptographic network security. Rate of bc hash functions consider des, the block size is 64 bits and key length 56 bits message digest only 64 bits. Message authentication codes macs based on universal hashfunction families are becoming increasingly popular due to their fast implementation. Safeguarding data using encryption nist computer security. Just as with symmetric and publickey encryption, we can group attacks on hash functions and macs into two categories. Hashing and macs hash functions create a short digital fingerprint of file or message highlyversatile, but often used to verify. Security of cryptographic hash functions wikipedia. Hash functions and message authentication codes mac. Compression arbitrary length input fixed length output 3. A variablelength plaintext is hashed into a fixedlength hash value often called a message digest or simply a hash. Tsudiac 18 has detailed a protocol based on the same idea.
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