Annex A.4: Skinny-128/256 example

What the clause requires

What the public text does not state

• The example values
• Any amendment change to the example

What it means for you

The Skinny-128/256 example is the middle version: a 128-bit block, the same block as Deoxys, with a 256-bit tweakey. It avoids the 64-bit data bound that clause 5 attaches to Skinny-64/192, so the evidence request can focus on the vector, the split and the build rather than on a volume calculation.

The comparison with Deoxys-TBC-256 is the useful question. Both have a 128-bit block and a 256-bit tweakey, and they are different algorithms with different round functions and different schedules. A buyer who treats the two names as interchangeable will get the claim, the test vector and the implementation review wrong. The record keeps them on separate pages for that reason.

The evidence is the familiar three. The fourth item, if the module is validated, is the test lab report. An internal vector is a good start; an external report is stronger, and the annex gives the evaluator the same reference point either way.

Evidence to keep

What an auditor or a customer is likely to ask for

Artefact	Owner	Why it matters
Known-answer test record for Skinny-128/256 with the five fields and the build	Engineering	The annex supplies the expected output.
Configuration record with the key and tweak lengths that sum to 256	Engineering	The 256-bit name does not fix the key length.
Comparison note against Deoxys-TBC-256, so the two are not conflated	Security architecture	Same lengths, different algorithm.

How to verify it

Ask which of the two 128/256 algorithms is deployed. If the answer is ambiguous, the test vector may be for the wrong family.

Dates

The kit plan for annex A.4 sets the evidence review at 17 June 2027, 90 days before the estimated publication date of 15 September 2027.

Cross references

• A Annex A, Numerical examples
• 7 Skinny
• 7.1 Skinny versions
• 7.2 Skinny encryption

Where this comes from