# 6.13.5.5 The group equation, with the curve parameters in hand

The verifier runs the signature equation with the curve parameters and the base point of the set, and accepts or rejects. Everything the equation needs has been checked in the preceding steps, so this step is arithmetic on values that are known to be in range and on the curve.

## What it asks

Run the equation with the parameters of the set the deployment uses, and record the accept and reject result for the worked examples. Where a library provides the whole verification, record which clause revision the library implements, because a library built before the amendment may not enforce the decoding rules.

## What the amendment does

Inserts 6.13.5.5.

## Who it binds

The verifier owner and the library owner.

## Evidence an auditor samples

- The worked example results, accept and reject, in the test log (test suite)
- The library version and its statement of the clause it implements (supplier file)
- The upgrade plan for any library that predates the amendment (remediation plan)

## The test you can run

Run the two worked examples and one mutated signature. Two accepts and one reject is the expected result; anything else is a finding.

## Common failures

- The library is assumed to implement the amendment because it supports the curve name.
- The verifier accepts a signature when the decode step was skipped.

## How to close it

The equation is the easy part. The evidence that matters is the negative case, because a verifier that always returns true still passes the positive example. Keep one mutated signature in the suite for exactly that reason.

## Source

ISO/IEC 14888-3:2018/FDAM 1:2026(en), draft, 6.13.5.5. Read on 21 October 2026. Our wording, not the instrument's.
https://www.iso.org/standard/89517.html

Not legal advice; does not certify.