Clause 7: Skinny

What the clause requires

What the public text does not state

• The body of clause 7 and its four subclauses
• The round function and schedule for any Skinny version

What it means for you

Skinny is the second family in the document and the one with three versions, including a 64-bit block. The ISO public preview gives the family name in the contents list and the three version names in Table 1, and it gives one requirement about the smallest version in clause 5. Everything else in clause 7 is outside the public text.

The three versions are Skinny-64/192, Skinny-128/256 and Skinny-128/384. The first number is the block length and the pair is the tweakey length, following the same naming convention as Deoxys. The 64-bit block is the reason clause 5 carries a data bound: a small block limits how much data can be processed under one key before the birthday bound matters.

The buyer s decision is therefore about the 64-bit version, not about Skinny as a whole. If the organisation uses a 128-bit Skinny version, the clause 5 bound does not apply by name. If it uses Skinny-64/192, the bound is the first thing to evidence. The page keeps that distinction and does not generalise the bound to the other versions.

Evidence to keep

What an auditor or a customer is likely to ask for

Artefact	Owner	Why it matters
Inventory row that names the Skinny version, block length and tweakey length	Security architecture	The three versions have different bounds and uses.
For Skinny-64/192, the data volume per key and the advantage bound	Engineering	Clause 5 ties this version to a bound below 2^64 blocks.
Purchase record for the base standard, so clause 7 can be read in full	Standards owner	The page states that the text is not in the public preview.

How to verify it

Ask which Skinny version is deployed. If the answer is "Skinny" without a version, the block length and the data bound are both unknown.

Dates

The kit plan for clause 7 sets the evidence review at 17 June 2027, 90 days before the estimated publication date of 15 September 2027.

Cross references

• 5 Requirements on the usage of tweakable block ciphers
• 7.1 Skinny versions
• 7.2 Skinny encryption
• 7.3 Skinny decryption
• 7.4 Skinny tweakey schedule
• A.3 Skinny-64/192 example
• A.4 Skinny-128/256 example
• A.5 Skinny-128/384 example

Where this comes from