# Introduction Four groups, and why the coupon strategy decides the work

The introduction sorts the mechanisms into four groups by the arithmetic each party performs. Two groups carry the cost on the claimant, one puts it on the verifier, and one avoids a coupon altogether. The grouping is the fastest way to see which clause a system belongs to.

## What it asks

Place every entity authentication mechanism in your estate into one of the four groups, and record the reason. A mechanism filed in the wrong group will be parameterised and tested against the wrong clause, which is the most common inventory error in this part.

## What the revision does

The fourth edition keeps the four-group description and will restate it against the revised clause order. The public record does not disclose the revised wording.

## Who it binds

The owner of the mechanism inventory and the architect who approves the mechanism set.

## Evidence an auditor samples

- The mechanism inventory, with one group per row and the reason for the placement (architecture)
- The clause each mechanism is tested against (test plan)
- The review note that accepted the grouping (review log)

## The test you can run

Pick a mechanism at random and ask which group it is in. If the answer is a product name rather than an arithmetic cost, the inventory is not grouped.

## Common failures

- Mechanisms are grouped by vendor rather than by arithmetic cost.
- A system is filed in two groups because nobody decided which clause governs it.

## How to close it

Group first, then parameterise. The group tells you whether the challenge size matters, whether a coupon is possible and which annex guidance applies, so an hour spent on the grouping saves a week of rework later.

## Source

ISO/IEC 9798-5:2009(E), Introduction, publisher preview; replaced by ISO/IEC DIS 9798-5, stage 40.20. Read on 21 October 2026. Our wording, not the instrument's.
https://www.iso.org/standard/89516.html

Not legal advice; does not certify.