spec-delta-checker

name	spec-delta-checker
description	Compare cryptographic code against a reference specification or paper. Use when implementation details look close to a standard but may have drifted in validation, transcript binding, parameter negotiation, or caller obligations.
allowed-tools	["Read","Grep","Glob"]

spec-delta-checker

Focused skill for specification-versus-implementation review.

Core principle: verify what the code actually enforces, not what the docs claim.

When to Use

• The implementation claims to follow a paper, RFC, or upstream reference crate
• You suspect the code omits a condition that the specification assumes
• Security depends on caller obligations that may not be enforced locally
• Protocol glue code appears to adapt a standard primitive or proof system

When NOT to Use

• Building initial context before you know which spec or paper governs the code
• Reporting a finding without first identifying the exact delta
• Writing final report prose without finishing the deviation review

Rationalizations to Reject

Rationalization	Why it is wrong
"The deviation is just a performance optimization"	Optimizations are a primary source of semantic-drift bugs
"The paper doesn't apply to this implementation"	If the code cites the paper, the deltas are audit surface
"The spec is ambiguous here"	Ambiguity in the spec plus code that picks one interpretation is still an untested assumption

Workflow

Execute workflows/delta-review.md in order. Treat every implementation delta as a potential finding candidate until you can prove it is benign.

Reference Use

• Use crypto-audit-context first if the target codebase is still unfamiliar
• Send surviving deviations to crypto-fp-check
• Use audit-common when the delta turns into a reportable finding

Output Contract

Produce a delta handoff that includes:

• The governing reference specification or paper
• The exact place where the implementation diverges
• Whether the delta changes enforcement, assumptions, or caller obligations
• The recommended next skill for validation or reporting