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In cryptography and computer security, a length extension attack is a type of attack where an attacker can use Hash(message 1) and the length of message 1 to calculate Hash(message 1 ‖ message 2) for an attacker-controlled message 2, without needing to know the content of message 1.
Cryptographic weaknesses were discovered in SHA-1, and the standard was no longer approved for most cryptographic uses after 2010. SHA-2: A family of two similar hash functions, with different block sizes, known as SHA-256 and SHA-512. They differ in the word size; SHA-256 uses 32-bit words where SHA-512 uses 64-bit words.
The Digital Signature Algorithm (DSA) is a public-key cryptosystem and Federal Information Processing Standard for digital signatures, based on the mathematical concept of modular exponentiation and the discrete logarithm problem.
A Kerberos standard in 2005 recommended 4,096 iterations; [1] Apple reportedly used 2,000 for iOS 3, and 10,000 for iOS 4; [4] while LastPass in 2011 used 5,000 iterations for JavaScript clients and 100,000 iterations for server-side hashing. [5] In 2023, OWASP recommended to use 600,000 iterations for PBKDF2-HMAC-SHA256 and 210,000 for PBKDF2 ...
SHA-2 basically consists of two hash algorithms: SHA-256 and SHA-512. SHA-224 is a variant of SHA-256 with different starting values and truncated output. SHA-384 and the lesser-known SHA-512/224 and SHA-512/256 are all variants of SHA-512. SHA-512 is more secure than SHA-256 and is commonly faster than SHA-256 on 64-bit machines such as AMD64.
SHA-256 hash function. Smart contracts use 256- or 257-bit integers; 256-bit words for the Ethereum Virtual Machine. "We realize that a 257 bits byte is quite unusual, but for smart contracts it is ok to have at least 256 bits numbers. The leading VM for smart contracts, Ethereum VM, introduced this practice and other blockchain VMs followed." [8]
When there is a set of n objects, if n is greater than |R|, which in this case R is the range of the hash value, the probability that there will be a hash collision is 1, meaning it is guaranteed to occur. [4] Another reason hash collisions are likely at some point in time stems from the idea of the birthday paradox in mathematics.
Salsa20 and the closely related ChaCha are stream ciphers developed by Daniel J. Bernstein.Salsa20, the original cipher, was designed in 2005, then later submitted to the eSTREAM European Union cryptographic validation process by Bernstein.