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# [WIP] SimpleSerialiZe (SSZ) # [WIP] SimpleSerialiZe (SSZ)
This is a **work in progress** describing typing, serialisation and Merkleisation of Ethereum 2.0 objects. This is a **work in progress** describing typing, serialization and Merkleization of Ethereum 2.0 objects.
## Table of contents ## Table of contents
@ -25,8 +25,8 @@ This is a **work in progress** describing typing, serialisation and Merkleisatio
| Name | Value | Definition | | Name | Value | Definition |
|-|:-:|-| |-|:-:|-|
| `LENGTH_BYTES` | 4 | Number of bytes for the length of variable-length serialized objects. | | `LENGTH_BYTES` | `4` | Number of bytes for the length of variable-length serialized objects. |
| `MAX_LENGTH` | 2**(8 * LENGTH_BYTES) | Maximum serialization length. | | `MAX_LENGTH` | `2**(8 * LENGTH_BYTES)` | Maximum serialization length. |
## Types ## Types
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## Deserialization ## Deserialization
Given a type, serialisation is an injective function from objects of that type to byte strings. That is, deserialisation—the inverse function—is well-defined. Given a type, serialization is an injective function from objects of that type to byte strings. That is, deserialization—the inverse function—is well-defined.
## Merkleization ## Merkleization
We first define helper functions: We first define helper functions:
* `pack`: Given ordered objects of the same basic type, serialise them, pack them into 32-byte chunks, right-pad the last chunk with zero bytes, and return the chunks. * `pack`: Given ordered objects of the same basic type, serialize them, pack them into 32-byte chunks, right-pad the last chunk with zero bytes, and return the chunks.
* `merkleise`: Given ordered 32-byte chunks, right-pad them with zero chunks to the closest power of two, Merkleize the chunks, and return the root. * `merkleize`: Given ordered 32-byte chunks, right-pad them with zero chunks to the closest power of two, Merkleize the chunks, and return the root.
* `mix_in_length`: Given a Merkle root `r` and a length `l` (32-byte little-endian serialisation) return `hash(r + l)`. * `mix_in_length`: Given a Merkle root `root` and a length `length` (32-byte little-endian serialization) return `hash(root + length)`.
Let `o` be an object. We now define object Merkleization `hash_tree_root(o)` recursively: Let `o` be an object. We now define object Merkleization `hash_tree_root(o)` recursively: