( 24th August 2019 )
A hash chain is the successive application of a cryptographic hash function to a piece of data.
For non-repudiation a hash function can be applied successively to additional pieces of data in order to record the chronology of data's existence.
A hash chain is a successive application of a cryptographic hash function h to a string x.
For example,
h(h(h(h(x)))) gives a hash chain of length 4, often denoted h4(x)
Fig 1.26: Hash chain
Fig: Binary Hash chain
Binary hash chains are commonly used in association with a hash tree. A Binary hash chain takes two hash values as inputs, concatenates them and applies a hash function to the result, thereby producing a third hash value.
1) Hash chain vs. Blockchain
A hash chain is similar to a blockchain, as they both utilize a cryptographic hash function for creating a link between two nodes. However, a blockchain (as used by Bitcoin and related systems) is generally intended to support distributed consensus around a public ledger (data), and incorporates a set of rules for encapsulation of data and associated data permissions.
2) SHA256d algorithms
SHA-2 (Secure Hash Algorithm 2) is a set of cryptographic hash functions designed by the United States National Security Agency (NSA).
It has a one-way compression function using the Davies-Meyer structure from a (classified) specialized block cipher.
SHA-2 is utilized in secured network communications, block chain applications including crypto currency.
Market requires enhance the hash rate by its computation power by CPU, GPU and ASIC.
Over clock drive, over voltage setting are main techniques.
Issues to enhance the hash rate by over clock drive, over voltage setting are:
1. Higher energy consumption.
2. Heavy heat from processing units.
3. Reduce the life time of processing unit.
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