* Implement tuples and a chunk-size reduction to 32 bytes (see #665 and #679)
* Simplify presentation where appropriate. For example, deserialisation is implicit from serialisation (similar to `bls_sign` being implicit from `bls_verify`) and is left as an implementation exercise.
* Dramatically reduce spec size and hopefully improve readability.
If this is accepted, then we can replace all uses of signing in the protocol, which are currently done in a relatively inconsistent way (see proposer signatures, attester signatures, shard proposer signatures, exit message signatures.....) could be unified.
Reasons to use `merkle_hash` instead of `hash` for containers:
1) **Smaller witnesses**: `BeaconState` is a somewhat wide container (26 fields as of now, likely 30+ in phase 2). With concatenation and plain concatenation the size of the Merkle witnesses for the top level are ~32 bytes per field element.
2) **Faster incremental hashing**
3) **Consistency**: Consistent with `merkle_hash` for lists/vectors.
The current spec is arguably inconsistent, in that if a set of N values gets chunked into M chunks where M is not an exact power of 2, the chunks between M and next_power_of_2(M) are filled with SSZ_CHUNK_SIZE zero bytes each, but the last chunk is not padded, and could be arbitrarily short (eg. if the values are 4 bytes and there are 257 of them, then that gets serialized into eight chunks chunks where the first four are 64 values each, the fifth is 4 bytes corresponding to the last value, and the last three chunks are SSZ_CHUNK_SIZE zero bytes). This PR fills every chunk up to exactly SSZ_CHUNK_SIZE bytes for consistency.
* pack small items tightly to fit more items in single chunk, decreasing
the number of hash operations needed
* remove chunk padding - hash algorithm will pad to its own block size
anyway
* express data length in number of items instead of binary bytes at leaf
level (equivalent)
* Added tree hashing algorithm
* Update simple-serialize.md
* add one more ref to tree_hash
* Add the zero-item special case
* list_to_glob to handle empty list
* refactor hash in simple serialize to support arbitrary byte length
* make comment clearer
* add deserialization of hashN
* formatting
* remove specific hash examples
Justin
sigmoid
vbuterin
Jordan Andrews
Hsiao-Wei Wang
jannikluhn
Chih Cheng Liang
Dean Eigenmann
Jacek Sieka
Danny Ryan
Cayman
Alex Stokes
terence tsao
Nishant Das
Chris Leishman
Antoine Toulme
Jacek Sieka
mratsim
Mikerah
Yutaro Mori