Clause 6.1: Deoxys-TBC versions

What the clause requires

Two versions are defined. Deoxys-TBC-256 has a 256-bit tweakey made of a key of at least 128 bits and a tweak of the remaining bits. Deoxys-TBC-384 has a 384-bit tweakey made of a key of at least 128 bits and a tweak of the remaining bits. The block is 128 bits in both.

What the public text does not state

• Whether the amendment adds a version or changes a length

What it means for you

The version names describe the tweakey, not the key. That single sentence resolves most of the confusion around this family. A Deoxys-TBC-256 configuration can have a 128-bit key and a 128-bit tweak, or a 192-bit key and a 64-bit tweak, or a 256-bit key and no tweak at all, provided the key floor in clause 5 is met. The name stays the same because the combined input stays 256 bits.

The clause also fixes the block at 128 bits for both versions. That is the length an inventory should record alongside the key and tweak lengths, because a mode built on the primitive will inherit it. A product that says only "Deoxys" has not told you which version, which split or which block length it uses.

For the record, this page is where a buyer checks a supplier answer. The three questions are: which version, what key length, what tweak length. If the answer gives only the version name, the key length is still unknown, and the 128-bit floor has not been demonstrated.

Evidence to keep

What an auditor or a customer is likely to ask for

Artefact	Owner	Why it matters
Configuration record naming the version and the key and tweak lengths separately	Engineering	The version name alone does not prove the key floor.
Supplier answer to the three-question request	Procurement	Turns a marketing claim into a checkable configuration.
Key inventory entry keyed by version and split	Security operations	The separation rule in clause 5 operates on the split.

How to verify it

Write the three numbers on one line: block, key, tweak. If any is missing, the configuration is not yet evidenced.

Dates

The kit plan for clause 6.1 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
• 6.2 Deoxys-TBC encryption
• A.1 Deoxys-TBC-256 example
• A.2 Deoxys-TBC-384 example

Where this comes from