Selected topics in cryptography solved exam problems enes pasalic university of primorska koper, 20. The compression property requires that messages of any length be hashed to a nite domain. To solve out this problem, this paper suggests mutual authentication rfid protocols that can guarantee safety from spoofing and retransfer attack and also reduce the number of comparative operations in the backend database, with the use of hash functions, xor. Ron rivests proposal for a modern cryptographically secure hash function. The hash function is based on xoring bits of the key. In this paper, we analyze the xor operator in the hash based flow selection function at the highspeed links, and prove that bit xor operator can increase the uniformity of distribution. A tabulation based hash function maps a key into d derived characters indexing random values in tables that are then combined with bitwise xor operations to give the hash. I hx x mod n is a hash function for integer keys i hx. To apply the constructed hash functions to the skewedassociative cache, we. In a damgardmerkle hash with a linearxor checksum, each bit of the checksum is a. It is a mathematical algorithm that maps data of arbitrary size often called the message to a bit string of a fixed size the hash value, hash, or message digest and is a oneway function, that is, a function which is practically infeasible to invert. Whats wrong with xor encryption with hash and an iterated. Selected topics in cryptography solved exam problems. Suppose i have two hash functions, of which neither or only one is collision resistant, and i want to create a new hash function by taking the bitwise exclusive or xor of the results of those two functions.
Cryptography based on hash function blake 32 in vlsi gibi sunny. 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 avalanche effect. In this paper, we design new xorbased hash functions, which compute each set index bit as xor of a subset of the bits in the address by using the concepts of. Haifa structure, extensibleoutput functions xofs design. Authentication code mac and the overall hash function as a keyed hash function. Hash functions and hash tables a hash function h maps keys of a given type to integers in a. Hashing for message authentication purdue college of engineering. Part of the lecture notes in computer science book series lncs, volume 4964. The xor cipher is often used in computer malware to make reverse engineering more difficult. A short universal hash function from bit rotation, and applications. When the keystream is generated by a pseudorandom number generator, the result is a stream cipher. Ultimately, the conclusion of this study is that xorbased placement functions unequivocally provide highly significant performance benefits to most cache organizations.
Assuming the hash is supposed to be x bytes long, break the message into blocks of x bytes. In this paper, we design new xorbased hash functions, which compute each set index bit as xor of a subset of the bits in the address by using the concepts of rank and null space. In this paper, we bring out the importance of hash functions, its various structures, design techniques, attacks and the progressive recent development in this field. Design of new xorbased hash functions for cache memories core. These are conflictfree hash functions which are of different types according to whether m is even or odd. A boolen hash function is given that takes a hexadecimal key as input and returns the hash for that key hash can be only 0 or 1. Four basic properties are typically desired of cryptographic hash functions. A dictionary is a set of strings and we can define a hash function as follows. Rfid mutual authentication protocols using key exchange. Eliminating cache conflict misses through xorbased.
Design of new xorbased hash functions for cache memories core reader. The xor encryption method should be used by itself. The scheme in figure 1c is a publickey encryption version of the scheme shown in figure 1b. New hash function based on chaos theory cha1 mahmoud maqableh, azman bin samsudin and mohammad a. The size of the hash value will be equal to the block length.
When implementing an xor based hash function, it is extremely important to understand what patterns are mapped conflictfree and how a hash function. Just like a hammer is good if you want to hit on nails, not so much if you want to feed a baby a baby bottle is better for that one main usage of hash functions is to get a digest which represents a given piece of data. Request pdf xorbased hash functions bank conflicts can severely reduce the bandwidth of an interleaved multibank memory and conflict misses increase. Is it possible for this new function to be collision resistant. Since circulant hash is an almost xoruniversal hash function for balanced inputoutput, it may not be a perfect substitute for h 3 and. Part of the lecture notes in computer science book series lncs, volume 8209. Alan kaminsky rochester institute of technology department of computer science february 17, 2004 oneway hash functions the secure hash algorithm family double hashing message authentication codes digital signatures encryption and. We survey theory and applications of cryptographic hash functions, such as md5 and sha1, especially their resistance to collision. In the symmetrickey encryption based scheme shown in figure. Intermediate state hash function compression function diamond structure generic attack. The preimage resistance and second preimage resistance properties are identical to the above apre and asec notions, respectively. Incremental multiset hash functions and their application to memory integrity checking dwaine clarke. If the key is random and is at least as long as the message, the xor cipher is much more secure than when there is key repetition within a message. Xor based hash functions, which compute each set index bit as the exclusiveor of a subset of the address bits.
Handbook of applied cryptography chapter 9 hash functions and data integrity pdf available d stinson. Using this algorithm, we set an upper bound on the conflict reduction achievable with xor functions. Any slight change to the message will change the hash. For example, an sample hash function in c would be written like this.
The hashcode of the message is encrypted with the senders private key. The sum can be weaker than each part cryptology eprint archive. Alia school of computer sciences, universiti sains malaysia, penang, malaysia summary cryptographic hash function has been used extensively in many cryptographic protocols. Cryptographic hash functions play an important central role in cryptology. Implementation is based on paritypreserving bit operations xor and.
Xor hash algorithm, every bit of the hashcode represents the parity at that bit. Suppose we need to store a dictionary in a hash table. Linearxor and additive checksums dont protect damgardmerkle. The value computed by applying the hash function to the key is often referred. You can be sure that you will get a good general understanding of algorithms if you spend time reading the book, solving problems. Thorup and zhang 2004 presented dwise independent tabulation based hash classes that use linear maps over finite fields to map a key, considered as a vector a,b, to. H is a hash function such as sha1, eis a symmetrickey encryption algorithm, \jj denotes simple. In a subsequent ballot round, landon curt noll improved on their algorithm.
This paper describes an algorithm to compute optimal xor functions, a particular type of hash functions based on xors. The md6 hash function free download as powerpoint presentation. We survey theory and applications of cryptographic hash functions, such as md5 and sha1, especially their resistance to collisionfinding attacks. Cryptography based on hash function blake 32 in vlsi. A family of keyed hash functions fk is epsilon, t, q, l weakly collisionresistant if adversary a. Cryptographic hash functions are used to achieve a number of security objectives. This is effectively the same as using method 1 with a key of x 0s. Learning what hash functions are and how mac functions are used. Constructing optimal xorfunctions to minimize cache. Cryprography theory and practice 3rd ed, chapter 4 security of hash functions s arora and b barak. But we can do better by using hash functions as follows. Next, we provide another novel algorithm to defeat additive checksums. When you want to find somebodys phone number, you search the book based on the name field.
Incremental multiset hash functions and their application. This is a list of hash functions, including cyclic redundancy checks, checksum functions, and. Design of new xorbased hash functions for cache memories. Hash functions, also referred to as message digests, do not use a key, but instead create a largely unique and fixedlength hash value, commonly referred to as a hash, based on the original message, something along the same lines as a fingerprint. We will discuss such applications of hash functions in greater detail in section 15. The attack is based on a novel technique to break the pairwise relationship between the. Or just use a hash function that does claim to be a prf when used this way. Of course, the book is also suitable for anybody else interested in competitive programming. A cryptographic hash function chf is a hash function that is suitable for use in cryptography. The md6 hash function 64 bit computing cryptography.
969 1531 88 1335 314 1390 900 1144 293 1408 975 1290 1102 1109 866 203 168 33 1408 866 708 651 673 647 1231 283 800 605 1408