Version 10 changes to composite signatures

[johngray-dev]

Here is the pull request with the updates for composite signatures:

Changes affecting interoperability:

• Changed all SEQUENCE OF SIZE (2..MAX) to SEQUENCE OF SIZE (2).
• Removed CompositeSignatureParams since all params are now explicit in the OID
• Made RSA keys fixed-length at 3072
• Removee redundency of subject public key overhead since OID fully specifies the keytype and parameters
• Re-worked wire format of the composite signature by prehashing and concatenating the OID to each component signature.

Editorial changes:

• Made this document standalone by folding in the minimum necessary content from composite-keys

• Added a paragraph describing how to reconstitute component SPKIs.

• Added a section showing the HEX encoding of the String Algorithm Names

• Added a section on pre-hashing

• Rename Dilithium to ML-DSA and Falcon to FN-DSA

• Added an Implementation Consideration about FIPS validation where only one component algorithm is FIPS-approved.

• TODO Refactored to use MartinThomson github template

• TODO Worked on Use cases references

• TODO Add Section on Signature APIs (Keygen, Sign, Verify) in introduction

[janklaussner]

Hi @johngray-dev, @ounsworth , @opencrypto

I finished the review and have some minor comments. If you agree I can gladly change them myself:

line 126: shall we still mention {{I-D.ounsworth-pq-composite-keys}}? I think we can remove this section already since we define structures for public and private keys now...

line 166: I want to add a third point:

• Safeguard against faulty algorithm implementations and compromised keys: Even for long known algorithms there is a non-negligible risk of severe implementation faults. Latest examples are the ROCA attack and ECDSA psychic signatures. Using more than one algorithms will also mitigate these risks.

line 318: here we say generation must fail on recursive composites, but the pseudo code does not include a check step like in the verification. Shall I add one for sake of uniformity?

line 320: I think this sentence has duplicate sections, I commited a fixed version.