Clause 1: Scope

What the clause requires

The base standard defines a tweakable block cipher as a family of n-bit permutations whose behaviour is set by a secret key and a public tweak, names five algorithms, and presents them as building blocks for schemes such as encryption, message authentication and authenticated encryption.

What the public text does not state

• The amendment body, including whether the table of five algorithms changes
• Any date for the amendment

What it means for you

This clause does the scoping work for the whole document. It tells you that the standard is about a primitive, not a product, a protocol or a mode of operation. The primitive takes a block, a key and a tweak, and returns a block. Anything built on top of it, such as an authenticated encryption scheme, is outside this clause and is named only as a use.

The clause also fixes the population. Five algorithms are in the document, and they are listed with a block length and a tweakey length. If a supplier says its module supports ISO/IEC 18033-7, the useful follow-up question is which of the five it implements and with what split between key and tweak.

The amendment applies to this document. The ISO record for the amendment says so in one line, and that is the whole of the public scope statement. The amendment body is not public, so this record cannot say which clause it changes, whether it adds an algorithm, or whether it touches the table of five. It states that limitation on every page rather than filling the gap with a guess.

Evidence to keep

What an auditor or a customer is likely to ask for

Artefact	Owner	Why it matters
Crypto inventory row naming the standard, the algorithm and the block and tweakey lengths	Security architecture	Shows the organisation knows which primitive it relies on, not just the product that ships it.
Datasheet or security target clause that cites the standard	Product management	A versioned claim is the thing a new amendment forces you to review.
Supplier declaration for any third-party module	Procurement	Moves the implementation question to the party that wrote the code.

How to verify it

Pick one product that uses a tweakable block cipher. Ask for the inventory row and the datasheet sentence. If either names the standard without the algorithm, the record is incomplete.

Dates

The kit plan for clause 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
• 6 Deoxys-TBC
• 7 Skinny
• B Annex B, Object identifiers

Where this comes from