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Signature hashing proposal #625

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merged 2 commits into from
Feb 16, 2019
Merged

Signature hashing proposal #625

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Signature hashing proposal
vbuterin Feb 14, 2019
385d06d
Update simple-serialize.md
JustinDrake Feb 14, 2019
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11 changes: 10 additions & 1 deletion specs/simple-serialize.md
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Original file line number Diff line number Diff line change
Expand Up @@ -24,11 +24,12 @@ deserializing objects and data types.
- [bytesN](#bytesn-1)
- [List/Vectors](#listvectors-1)
- [Container](#container-1)
+ [Tree Hash](#tree-hash)
+ [Tree Hash](#tree-hash)
- [`uint8`..`uint256`, `bool`, `bytes1`..`bytes32`](#uint8uint256-bool-bytes1bytes32)
- [`uint264`..`uintN`, `bytes33`..`bytesN`](#uint264uintn-bytes33bytesn)
- [List/Vectors](#listvectors-2)
- [Container](#container-2)
+ [Signed Roots](#signed-roots)
* [Implementations](#implementations)

## About
Expand Down Expand Up @@ -396,6 +397,14 @@ Recursively tree hash the values in the container in the same order as the field
return merkle_hash([hash_tree_root_internal(getattr(x, field)) for field in value.fields])
```

### Signed roots

Let `field_name` be a field name in an SSZ container `container`. We define `truncate(container, field_name)` to be the `container` with the fields from `field_name` onwards truncated away. That is, `truncate(container, field_name) = [getattr(container, field)) for field in value.fields[:i]]` where `i = value.fields.index(field_name)`.

When `field_name` maps to a signature (e.g. a BLS12-381 signature of type `Bytes96`) the convention is that the corresponding signed message be `signed_root(container, field_name) = hash_tree_root(truncate(container, field_name))`. For example if `container = {"foo": sub_object_1, "bar": sub_object_2, "signature": bytes96, "baz": sub_object_3}` then `signed_root(container, "signature") = merkle_hash([hash_tree_root(sub_object_1), hash_tree_root(sub_object_2)])`.

Note that this convention means that fields after the signature are _not_ signed over. If there are multiple signatures in `container` then those are expected to be signing over the fields in the order specified. If multiple signatures of the same value are expected the convention is that the signature field be an array of signatures.

## Implementations

| Language | Implementation | Description |
Expand Down