ADR 007: Solo machine signature construction (cosmos#1865)

## Description



closes: cosmos#1847 

---

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docs/architecture/adr-007-solomachine-signbytes.md

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+# ADR 007: Solo machine sign bytes
+
+## Changelog
+* 2022-08-02: Initial draft
+
+## Status
+
+Accepted, applied in v6
+
+## Context
+
+The `06-solomachine` implemention up until ibc-go v6 constructed sign bytes using a `DataType` which described what type of data was being signed. 
+This design decision arose from a misunderstanding of the security implications.
+It was noted that the proto definitions do not [provide uniqueness](https://github.com/cosmos/cosmos-sdk/pull/7237#discussion_r484264573) which is a necessity for ensuring two signatures over different data types can never be the same.
+What was missed is that the uniqueness is not provided by the proto definition, but by the usage of the proto definition. 
+The path provided by core IBC will be unique and is already encoded into the signature data.
+Thus two different paths with the same data values will encode differently which provides signature uniqueness. 
+
+Furthermore, the current construction does not support the proposed changes in the spec repo to support [Generic Verification functions](https://github.com/cosmos/ibc/issues/684).
+This is because in order to verify a new path, a new `DataType` must be added for that path. 
+
+## Decision
+
+Remove `DataType` and change the `DataType` in the `SignBytes` and `SignatureAndData` to be `Path`. 
+The new `Path` field should be bytes. 
+Remove all `...Data` proto definitions except for `HeaderData`
+These `...Data` definitions were created previously for each `DataType`.
+The proto version of the solo machine proto definitions should be bumped to `v3`. 
+
+This removes an extra layer of complexity from signature construction and allows for support of generic verification.
+
+## Consequences
+
+### Positive
+- Simplification of solo machine signature construction
+- Support for generic verification 
+
+### Negative
+- Breaks existing signature construction in a non-backwards compatible way
+- Solo machines must update to handle the new format
+- Migration required for solo machine client and consensus states
+
+### Neutral
+No notable consequences
+
+## References
+
+* [#1141](https://github.com/cosmos/ibc-go/issues/1141)