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Merge pull request #32 from ethereum/JustinDrake-patch-3 

Rework Appendix A on hash functions
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Danny Ryan 2018-10-03 09:16:23 -05:00 committed by GitHub
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@ -634,12 +634,8 @@ Slashing conditions may include:
# Appendix
## Appendix A - Hash function
The general hash function `hash(x)` in this specification is defined as:
`hash(x) := BLAKE2b-512(x)[0:32]`, where `BLAKE2b-512` (`blake2b512`) algorithm is defined in [RFC 7693](https://tools.ietf.org/html/rfc7693) and input `x` is bytes type.
* `BLAKE2b-512` is the *default* `BLAKE2b` algorithm with 64-byte digest size. To get a 32-byte result, the general hash function output is defined as the leftmost `32` bytes of `BLAKE2b-512` hash output.
* The design rationale is keeping using the default algorithm and avoiding too much dependency on external hash function libraries.
We aim to have a STARK-friendly hash function `hash(x)` for the production launch of the beacon chain. While the standardisation process for a STARK-friendly hash function takes place—led by STARKware, who will produce a detailed report with recommendations—we use `BLAKE2b-512` as a placeholder. Specifically, we set `hash(x) := BLAKE2b-512(x)[0:32]` where the `BLAKE2b-512` algorithm is defined in [RFC 7693](https://tools.ietf.org/html/rfc7693) and the input `x` is of type `bytes`.
## Copyright
Copyright and related rights waived via [CC0](https://creativecommons.org/publicdomain/zero/1.0/).