In Focus

// Research series

Format-Preserving Encryption

What format-preserving encryption reveals, how its modes differ and why migration is hard to infer from ciphertext alone.

2-part series · Read in order

// Reading path

From first question to final consequence.

All series →
  1. Part 1Preserving the format preserves the leakage.Format-preserving encryption keeps ciphertext compatible with narrow legacy fields. It also keeps domain size, length, structure and often equality visible.
  2. Part 2The ciphertext does not say which mode produced it.Format-preserving ciphertext carries no mode, key or tweak metadata. That convenience makes FF1 and FF3 migration difficult to scope from the data alone.
Preserving the format preserves the leakage.

Preserving the format preserves the leakage.

by | May 4, 2026 | Research

FORMAT-PRESERVING ENCRYPTION What format-preserving encryption keeps visible in order to remain compatible. Legacy systems often require a value to remain decimal, retain its length and pass through fields designed for an account number or identifier. Conventional...
The ciphertext does not say which mode produced it.

The ciphertext does not say which mode produced it.

by | May 9, 2026 | Research

FORMAT-PRESERVING ENCRYPTION The current revision draft removes FF3, requires a larger minimum domain, and the values in the database carry no metadata about how they were made. The earlier article set out what format-preserving encryption leaves visible. This one is...