Cmac may be appropriate for information systems in which an approved block cipher is more readily available than an approved hash function. It is called a doubleblocklength dbl hash function if its output length is twice larger than the block length. In fact, such assumptions are often made without much regard for the actual constructions of these primitives. Ciphers, their security and implementation properties seminararbeit timo bartkewitz ruhruniversity bochum february 23, 2009 abstract this work deals with methods to construct a hash function containing a compression function that is built from a block cipher. Blackbox analysis of the blockcipherbased hashfunction. Des is the best known and most widely used encryption function in the commercial world today. Hash function coverts data of arbitrary length to a fixed length. Recent contributions to cryptographic hash functions 83 compression functions th e compression functions for all the hash functions commonly used today are built in the following way. Possible size values vary between 8 and b8 bits, where b is the data block size of the underlying cipher. An iterated hash function whose compression function is composed of a block cipher is called a singleblocklength sbl hash function if its output length is equal to the block length of the block cipher. Intel ipp function apis of the ofb mode contain the ofbblksize parameter, which represents size of the feedback. In this paper, we describe whirlpool, which is a block cipher based secure hash function. Block cipher and stream cipher are the methods used for converting the plain text into cipher text directly and belong to the family of symmetric key ciphers. Vanstone, handbook of applied cryptography crc press, 1997, page 340.
Iterated hash functions urepeat use of block cipher or custom function pad input to some multiple of block length iterate a lengthreducing function f f. New design criteria for hash functions and block ciphers. The major difference between a block cipher and a stream cipher is that the block cipher encrypts and decrypts a block of the text at a time. A modi cation to a ciphertext block will a ect that plaintext block and the one immediately following it, but none after that. A synthetic indifferentiability analysis of some blockcipher. Although most of the existing hash functions can be described as being based on a block cipher, these block cipher based hash functions can be further classified into two categories. Revisiting cryptographic hashing functions cryptology eprint. This property directly addresses many attacks on hash functions, and greatly improves. E cient and secure multiparty computation from fixedkey. There should be no way to deduce the key given any number of pairs b,gb in b,c, and no way to deduce gb from b, or b from gb. This thesis contains a new approach to design block ciphers, synchronous and selfsynchronizing stream ciphers and cryptographic hash functions. Ofbmode and ctr mode are block modes that turn a block cipher into a stream cipher. Building hash functions from block ciphers, their security and. We provide provably secure constructions, in the randompermutation model, of hash functions satisfying the di erent notions of pseudorandomness we consider.
A block cipher mode, or mode, for short, is an algorithm that features the use of a symmetric key block cipher algorithm to provide an information service, such as confidentiality or authentication. This method differs from hmac because it uses one algorithm. Its easy to see that you could replace the hash function and get an entirely new type of algorithm. A simple block cipher based on the sha256 hash function. Since a hash is a smaller representation of a larger data, it is also referred to as a digest. It is now considered as a broken block cipher, due primarily to its small key size. For example the sha256 hash function produces a 256. Shrimpton may 31, 2002 an abridged version, reference 2, appears as advances in cryptology crypto 02, lecture notes in computer. Five attacks on an iterated hash function and on its round function are. As such it is a block cipher with a 256 bit 32 byte block size and an arbitrary key length. Whirlpool produces a hash code of 512 bits for an input message of maximum length less than 2256 bits. Introduction single block hash double block hash hash based on.
Difference between block cipher and stream cipher with. Iterated hash functions based on block ciphers are treated. It is called a double block length dbl hash function if its output length is twice larger than the block length. Basic concepts in cryptography fiveminute university. This process is often referred to as hashing the data. There is a vast number of block ciphers schemes that are in use. Five drbg algorithms based on hash functions and block ciphers. Information technology security techniques hashfunctions part 2. I recently saw a blog post that discussed using rc4 as an adhoc hash in order to show why cbc mode is better than ecb. What role do hashing algorithms and block ciphers play in random number generation. Cryptographic hash functions can be built using block ciphers.
The use of a tweakable block cipher allows skein to hash con guration data along with the input text in every block, and make every instance of the compression function unique. In cipher block chaining cbc mode, the first block of the plaintext is exclusiveord xord, which is a binary function or operation that compares two bits and alters the output with a third bit, with an initialization vector iv prior to the application of the encryption key. Hash functions based on cipher block chaining questions. In this thesis, we address this problem and suggest new, and possibly better, design criteria for hash functions and block ciphers. In this paper, we describe whirlpool, which is a blockcipherbased secure hash function. Currently, nist has approved fourteen modes of the approved block ciphers in a series of special publications. This is a chapter from the handbook of applied cryptography. Taken together, our results provide endtoend security proofs for implementations of securecomputation protocols based on xedkey block ciphers modeled as random permutations. Cipher and hash function design strategies based on linear and. Pdf hash functions based on block ciphers researchgate.
Information technology security techniques hash functions part 2. Hash functions and mac algorithms based on block ciphers. Recommendation for b lock cipher modes of operation. When the blocklength and keylength are n 128 bits, as with mdc2 based on aes128, an ad. The basic cipher block chaining mac algorithm cbc mac has security deficiencies 9. Finally, three new hash round functions based on an mbit block cipher with a 2m bit key are proposed. A 128bit block cipher bruce schneier john kelseyy doug whitingz david wagnerx chris hall niels ferguson k 15 june 1998 abstract two sh is a 128bit block cipher that accepts a variablelength key up to 256 bits. Kxbc, which maps a key in k and a block in b into a block in c. For blockcipherbased hash codes, proposed designs have a hash code length equal to either the cipher block length or twice the cipher block length. The hash rate of a hash function based on an mbit block cipher is defined as the number of mbit message blocks hashed per encryption. Each plaintext block can be computed using only two ciphertext blocks, independent of the other plaintext blocks. Description of sha256 the sha256 compression function op erates on a 512bit message blo ck and a 256bit interme diate hash value.
I read about pseudo random number generators and there were certain demands on which underlying hash function and underlying block cipher to use. Building hash functions from block ciphers, their security and implementation properties seminararbeit timo bartkewitz ruhruniversity bochum february 23, 2009 abstract this work deals with methods to construct a hash function containing a compression function that is built from a block cipher. It was designed by the united states national security agency, and is a u. Revisiting dedicated and block cipher based hash functions. Most popular and prominent block ciphers are listed below. A ciphertext can be decrypted with a decryption key hashes have no. Some plausible constructions of doubleblocklength hash.
That said, thomas is right do not build your own crypto. Constructions for hash functions baaed on a block cipher are. Many other slides are from dan bonehsjune 2012 coursera crypto class. Blackbox analysis of the block cipher based hashfunction constructions from pgv j.
Moreover, they can yield a collision resistant hash function if a block cipher with sufficiently large block length is available. An iterated hash function whose compression function is composed of a block cipher is called a single block length sbl hash function if its output length is equal to the block length of the block cipher. Analysis and design of cryptographic hash functions, mac. Hash functions based on block ciphers 1 introduction. See oneway compression function for descriptions of several such methods. A cryptographic hash function must have certain properties. Sep 16, 2017 block cipher and stream cipher are the methods used for converting the plain text into cipher text directly and belong to the family of symmetric key ciphers. It is possible to use a hash function like sha family, for instance in ofb or cfb and possibly ctr, by using the hash function with the key as part of the input. The methods resemble the block cipher modes of operation usually used for encryption. The second category is the hash functions that use block ciphers that have been designed particularly for use in hash functions. While the authors example is merely an attempt to create a graphic, it reminded me to explain why a stream cipher shouldnt be used as as a cryptographic hash. This work deals with methods to construct a hash function containing a compression function that is built from a block cipher.
It is essen tially a 256bit blo c k cipher algorithm whic h encrypts the in termediate hash v alue using the message blo c. Five drbg algorithms based on hash functions and block. Cipher block chaining message authentication code cbcmac uses the cbc mode of a symmetric block cipher such as des to create a message authentication code mac. Building hash functions from block ciphers, their security. Our result, which is in the ideal cipher model, shows that mdc2, when built from a blockcipher having block length and keylength n, has security much better than that delivered by any hash function that has an nbit output.
They are therefore suitable for an environment in which such an algorithm is already implemented. Hash algorithms based on block ciphers special algorithms, e. Block ciphers, cryptographic hash functions, modes of operation, proving security. Usually b and c are the same set, so the block cipher permutes b in a keyspecific way. The various hash function design philosophies try to build the compression functions from different angles. Section 3 and we explore whether a block cipher makes an appropriate starting point for a compact hash function instead of a dedicated design. Blackbox analysis of the blockcipherbased hashfunction constructions from pgv j.
Merkie xerox parc 3333 coyote hill rd palo alto, ca. Skeins novel idea is to build a hash function out of a tweakable block cipher. The first 30 years of cryptographic hash functions and the. Ive come up with this little routine for doing encryption using the sha2 in this case sha256 hash function. The general model for the round function of the hash functions that will be studied in this extended abstract is depicted in fig. In general, the hash is much smaller than the input data, hence hash functions are sometimes called compression functions.
For block cipher based hash codes, proposed designs have a hash code length equal to either the cipher block length or twice the cipher block length. The main focus of this chapter is symmetrickey block ciphers. A hash function is typically based on an internal compression function f that works on fixedsize input blocks mi sort of like a chained block cipher produces a hash value for each fixedsize block based on 1 its content and 2 hash value for the previous block. A hash is used to take a message of any length and produces a fixedsized output length using a hash function.
Symmetric cryptography an overview sciencedirect topics. There are many schemes to turn a block cipher into a compression function, here. Lncs 4515 the collision intractability of mdc2 in the. Finally, three new hash round functions based on an mbit block cipher with a 2mbit key are proposed. In cryptography, sha1 secure hash algorithm 1 is a cryptographic hash function which takes an input and produces a 160 bit 20 byte hash value known as a message digest typically rendered as a hexadecimal number, 40 digits long. Why stream ciphers shouldnt be used for hashing rdist.
1102 1168 1384 1217 1021 582 446 1011 707 1294 518 905 1368 702 531 1116 1219 859 738 108 687 691 1154 660 993 221 394 686 163 861 1329 1283 683 355 330 1354 1382 911 612