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Tokenizing card numbers and SSNs with format-preserving encryption
The same use case told visually, ready to present. Speaker notes carry the full explanation.
Data Protection
Format-preserving tokenization
Protecting card numbers and SSNs in fields that can't change shape
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The problem
AES-GCM is the wrong shape here
Every column, interface and validation rule would have to change
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Two designs
A vault, or a key
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Worked example
Tokenizing 4111 1111 1111 1111
The tweak stops an encrypted middle being moved onto another card's digits
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Domain size
How many digits does FF1 get?
SP 800-38G Rev. 1 requires at least 1,000,000 values
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Small domains
SSNs: big enough for the standard, small enough to enumerate
Access control on tokenize matters as much as the key
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Which mode
Why FF1, and not FF3-1
Put existing FF3 or FF3-1 deployments on a migration list
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Operations
Keys, rotation and scope
Whether scope shrinks is an assessor's call, not the algorithm's
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Keys: ← → move, F full screen, G all slides, N notes