Determinism

Pseudonymize.io uses deterministic mapping to ensure the same identifier becomes the same pseudonym, preserving data integrity for downstream models.

How it works

By default, when alias_format is set to hash, we generate pseudonyms using HMAC(secret, normalized_value).

1. Normalization: The input [email protected] and [email protected] are both normalized to [email protected].
2. Key ownership: The secret is an ephemeral salt generated at the beginning of the Request scope. It is never stored.
3. Hashing: The normalized value is hashed.
4. Prefixing: The hash is truncated and prepended with the entity type (e.g. EMAIL_a1b2c3d4).

Security Properties

Because the secret salt is ephemeral (in Request scope) or strictly isolated to your project (in Project scope), attackers cannot pre-compute rainbow tables to guess the original values from the hashes.

If you use the open-source engine locally, you are entirely responsible for the generation, rotation, and security of the salt used for deterministic generation.