K3 Key variants

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Lesson K3: Binding a key to its use by XOR with a variant constant, and why key blocks replaced variants.

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The opening of the lesson

Why it matters

A key must only ever do one job. A PIN key that can also be used as a data key lets an attacker ask the HSM to "decrypt this data" and get PINs back. Before key blocks, the industry enforced this with key variants.

Variants are still in every Atalla- or Thales-style HSM interface, in legacy key exchanges and in DUKPT. If you integrate with an HSM or migrate a legacy host, you will meet them.

In the full lesson

The concept
Step by step
Why key blocks replaced variants
Common mistakes
What to test

What module K3 covers →

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