The sender uses some publicly known MAC algorithm, inputs the message and the secret key K and produces a MAC value. Exercise 11.1: Forouzan,B.A. Message authentication code (MAC) Hash functions, including Modification Detection Code (MDC) processing and one-way hash generation; Note: You can also use digital signatures (see Using digital signatures) to authenticate messages. (Assume that 1 Hash function (formal definition) n nn ln Gen H Gen s I I x * () is implicit in .) The basic idea is to concatenate the key and the message, and hash them together. Hash Functions in System Security Last Updated: 07-02-2018 Hash Function is a function which has a huge role in making a System Secure as it converts normal data given to it as an irregular value of fixed length. Building on hash functions, the course describes message authentication focusing on message authentication code (MAC) based on symmetric keys. Secure Hash Algorithm 1: The Secure Hash Algorithm 1 (SHA-1) is a cryptographic computer security algorithm. Constructing MACs MAC from hash functions MACs are keyed hash functions, so it is natural to use hash functions in a way that uses secret keys. Similar to hash, MAC function also compresses an arbitrary long input into a fixed length output. Just as with encryption algorithms and hash functions, we can group attacks on MACs into two categories: brute-force attacks and cryptanalysis. Here, we assume that the … 3. a variable length one-way hash function designed by Uni of Wollongong and recently published at Auscrypt'92 it processes messages in 1024-bit blocks, using an 8-word buffer and 3 to 5 rounds of 16 steps each, creating hash values of 128, 160, 192, 224, or 256 bits in length ECE/CS 5560, Fall 2020 2 Agenda Generating authenticators Message encryption MAC Hash functions Security of hash functions and MACs SHA-512 SHA3 HMAC. authentication is to use one-way hash functions instead of MAC; • The main difference is hash functions don’t use a secret key: h = H(M); • “One-way” in the name refers to the property of such functions: they are easy to compute, but their reverse functions are very difficult to compute. Various bitwise operations (e.g. • good for data integrity but useless for security Hash Function Requirements Attacks on Hash FunctionsAttacks on Hash Functions • have brute -force attacks and cryptanalysis • a preimage or second preimage attack • find ys.t . analysing the security of the standard hash function Cellular Authentication and Voice Encryption Algorithm (CAVE) used for authentication and key-derivation in the second generation (2G) North American IS-41 mobile phone system. rotations), modular additions and compression functions are used in iterative mode to ensure high complexity and pseudo-randomness of the output. It was designed by the United States National Security Agency, and is a U.S. Federal Information Processing Standard. c) Distinguish between an MDC and a MAC. b) Define the criterions for a cryptographic hash function. If the hash function used by a blockchain is broken, then an attacker could find collisions for crucial hash values (such as the block’s chains or a Merkle tree’s values). . It contrasts MAC with hash functions or general encryption/decryption techniques and quantify the brute force attack difficulty for MAC and discuss the security requirements for MAC. A brute-force attack on a MAC is a more difficult undertaking than a brute-force attack on a hash function because it requires known message-tag pairs. Most hash functions are built on an ad hoc basis, where the bits of the message are nicely mixed to produce the hash. It works by transforming the data using a hash function: an algorithm that consists of bitwise operations, modular additions, and compression functions. Given some pairs of messages and their MACs, Eve can The security of a MAC depends on the security of the underlying hash algorithm. Hash functions in Security • Digital signatures • Random number generation • Key updates and derivations • One way functions • MAC CR • Detect malware in code • User authentication (storing passwords) 7. 2 If such complexity is the best that can be achieved by an adversary, then the hash function is said to achieve ideal security. HMAC is a recipe for turning hash functions (such as MD5 or SHA256) into MACs. In this way, the security is very hard to prove and the proof is usually not done. If size of the key allows exhaustive search, Eve may try all possible keys to digest the message. The major difference between hash and MAC is that MAC uses secret key during the compression. To be considered secure, a MAC function must resist existential forgery under chosen-plaintext attacks. There are other ways of constructing MAC algorithms; CMAC, for example, is a recipe for turning a blockcipher into a MAC (giving us CMAC-AES, CMAC-DES, CMAC-PRINCE, and the like). A hash function is a mathematical function that converts a numerical input value into another compressed numerical value. function and PRF –Principle: computationally indistinguishable functions • Semantic security (computationally secure encryption): Adversary picks m 0,m 1, receives encryption of one of them, can’t do better than guessing on which messages was encrypted. The hash function then produces a fixed-size string that looks nothing like the original. in particular, it should be unfeasible to produce the MAC of a new message if the MAC of an old message is known. Regardless of how the hash function is designed, an attacker will be able to find preimages or second preimages after trying out N =2 n different messages, or find a pair of collision messages after trying out 2 n /2 different messages based on birthday paradox. MAC Requirements 2:28. The idea behind MAC is I compute a cryptographic hash function, perhaps MD5 or SHA-1, over both the block of data that I want to send, and a secret key that we share. MAC Security How can Eve forge a message without having the key? SECURITY OF MACS . An HMAC is a MAC which is based on a hash function. A (with output length ( )) is a pair of PPT al hash function gorithms ( , ): (1 ) outputs a key for some index set . A hash function. 1. Brute-Force Attacks. … h. maps arbitrary strings of data to fixed length output. The sender forwards the message along with the MAC. We de ne a MAC for arbitrary-length messages by Mac s;k(m) = Hs(kjjm): (a) Show that this is not a secure MAC if H is constructed by the Merkle-Damgard transform from an arbitrary collision-resistant hash function h. (We assume that s … While MAC functions are similar to cryptographic hash functions, they possess different security requirements. 2. Taught By. The function is deterministic and public, but the mapping should look “random”. . Information security — Message authentication codes (MACs) — Part 2: Mechanisms using a dedicated hash-function Message Authentication Codes, its requirements and security, MACs based on Hash Functions, Macs based on Block Ciphers 3. Secure Hash Algorithms, also known as SHA, are a family of cryptographic functions designed to keep data secured. The module also reviews two MAC implementations in Data Authentication Algorithm (DAA) and Cipher-Based MAC (CMAC), which are based on the use of block ciphers. Since it is impossible, given a cryptographic hash, to find out what it is the hash of, knowing the hash (or even a collection of such hashes) does not make it possible to find the key. 19 Universal hash family • Notations: – X is a set of possible messages – Y is a finite set of possible message digests or authentication tags? You append the same shared secret key to the block of data and compute the same hash function. In other words, h ∗: {0, d1} →{0, 1} for a fixed. Singapore: McGraw-Hill, 2008. 8. So HMAC-MD5 and HMAC-SHA256 are specific MAC algorithms, just like QuickSort is a specific sorting algorithm. Let us see why this is so. 7. The input to the hash function is of arbitrary length but output is always of fixed length. In addition, this thesis studies the analysis issues of message authentication codes (MACs) designed using hash functions. . Hash functions are extremely useful and appear in almost all information security applications. . Other Hash Functions HAVAL. A message authentication code (MAC) is a set of functions {MACk(x) : k∈ K} such that MACk: {0,1}∗→ {0,1}l. Note that this is exactly the same definition as a hash family. Hash functions • Random oracle model • Desirable Properties • Applications to security. Use preimage attack. x’ x’’ x y’ y hash function H Hash function H is a lossy compression function • Collision: H(x)=H(x’) for some inputs x≠x’ H(x) should look “random” • Every bit (almost) equally likely to be 0 or 1 A cryptographic hash function must have certain properties “message digest” message . Unformatted text preview: Cryptography and Network Security Chapter 12 Fourth Edition by William Stallings Lecture slides by Lawrie Brown Chapter 12 – Hash and MAC Algorithms Each of the messages, like each one he had ever read of Stern's commands, began with a number and ended with a number or row of numbers. With the aim to propose some efficient … The choice of verb depends on the security requirements of the environment in which you are operating. takes as input a key and a string {0,1} and outputs a string ( ) {0,1} . resistant hash function with inputs of arbitrary size. 8 %. The principle behind MACs The security properties that can be achieved with MACs How MACscan be realized with hash functions and with block ciphers Content of this part. 10 %. 1 Hash Functions. The security requirements for MACs are only people having the shared key should be able to produce MACs or verify MACs. Thus, no hash function would be collision resistant. (page 358) 1.25 Hash function security for blockchain. Hash functions are vital to protecting the immutability of the digital ledger. 6 . This course reviews cryptographic hash functions in general and their use in the forms of hash chain and hash tree (Merkle tree). Hash functions : MAC / HMAC Outline • Message Authentication Codes • Keyed hash family • Unconditionally Secure MACs • Ref: D Stinson: Cryprography – Theory and Practice (3rd ed), Chap 4. It was created by the US National Security Agency in 1995, after the SHA-0 algorithm in 1993, and it is part of the Digital Signature Algorithm or the Digital Signature Standard (DSS). Hash Functions: Main Idea bit strings of any length n-bit strings . I then transmit the block of data and the hash to you. Cryptography and Network Security (International Edition). Digital Signature, its properties Digital Signature, its properties, requirements and security, various digital signature schemes (Elgamal and Schnorr), NIST digital Signature algorithm 4. In cryptography, SHA-1 (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. d. Hash functions do not have a secret key.