Clause 7.1: Skinny versions

What the clause requires

What the public text does not state

• The body of clause 7.1
• Whether the amendment adds a version

What it means for you

The version table is the part of this clause a buyer can use without the body. Three versions are in the standard, with block lengths of 64 or 128 bits and tweakey lengths of 192, 256 or 384 bits. The naming convention follows Deoxys: the first number is the block, the pair is the tweakey, and the key is a subset of the tweakey with a floor of 128 bits.

The version choice is a design decision with a security consequence. The 64-bit block supports a smaller state and is the version clause 5 limits by data volume. The 128-bit versions avoid that specific bound but may have different performance and different mode constraints. The standard does not rank the versions in the public text; it defines them.

For the record, this page is a prompt to ask three questions: which version, what key length, what tweak length. The first is answerable from a datasheet. The second and third often are not, which is why the page keeps them separate from the version name.

Evidence to keep

What an auditor or a customer is likely to ask for

Artefact	Owner	Why it matters
Configuration record with the version and the key and tweak lengths	Engineering	The version name does not fix the key length.
Design decision record for choosing a 64-bit or 128-bit block	Security architecture	Shows the data bound was considered.
Mode and protocol constraints for the chosen version	Engineering	A small block can limit the modes that fit.

How to verify it

Read the datasheet for a block length. If it says only "Skinny", the version is missing.

Dates

The kit plan for clause 7.1 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 Skinny
• 7.2 Skinny encryption
• A.3 Skinny-64/192 example
• A.4 Skinny-128/256 example
• A.5 Skinny-128/384 example

Where this comes from