[sbazerque]

Exactly this. You need deterministic serialization, because you need to be sure that when the _same_ object is constructed in different settings, it is going to hash consistently. In Hyper Hyper Space [1], the set of basic types as well as the composition primitives used to construct all data structures have built-in deterministic serialization, just for this reason (e.g. a set will serialize into a deterministically ordered list, etc.)

[1] https://www.hyperhyperspace.org

[formerly_proven]

> Exactly this. You need deterministic serialization, because you need to be sure that when the _same_ object is constructed in different settings, it is going to hash consistently.

I can see how this might matter in some specific systems, but when we're talking about signatures only the signer constructs the object. Stuff like the "JWS/CT using JWS and JSON Canonicalization" recommended in a sibling comment is a complete misdesign for virtually all signing use cases. That's why "our signature scheme requires canonical representations" is a red flag.

[sbazerque]

But "the signer" here is a cryptographic identity, that may be present in more than one device. So, even when conceptually it is just one entity, in practice it may be several computers doing something independently, and one may need the result to be the same given identical inputs.