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Rehydration is the step that turns placeholder-based text back into its original values. It only works when the text was produced in pseudonymize mode and you still have the matching encryption key.

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When Rehydration Is Possible

Rehydration requires all of the following:
  • The text was processed in pseudonymize mode
  • You kept the returned encrypted piiMap
  • You still have the correct key to decrypt that piiMap
If any of these are missing, rehydration cannot restore the originals.

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Basic Flow

import { decryptPIIMap, rehydrate } from 'rehydra';

const key = await keyProvider.getKey();
const piiMap = await decryptPIIMap(result.piiMap, key);
const restored = rehydrate(textWithPlaceholders, piiMap);

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What Rehydration Uses

Rehydra matches placeholders such as <PII type="EMAIL" id="1"/> (or custom formats like [[PII type="EMAIL" id="1"]]) against the decrypted map and replaces them with the original values. This means the placeholder structure must stay intact between protection and restoration. If you used a custom tagFormat during anonymization, pass the same format to rehydrate().

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Rehydration vs Anonymization

WorkflowpiiMap existsOriginals recoverable
pseudonymizeYesYes
anonymizeNoNo

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Common Failure Modes

  • Using the wrong key
  • Losing the encrypted piiMap
  • Running in anonymize mode instead of pseudonymize
  • Modifying placeholder tags so they no longer match the stored mapping

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Where It Shows Up

Rehydration is part of:
  • SDK workflows using decryptPIIMap() and rehydrate()
  • CLI workflows using rehydra rehydrate
  • Agent and plugin flows that restore values locally before tool execution

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Next Steps

Encryption & Security

Learn how piiMap data and keys are handled.

Anonymization & Pseudonymization

See how reversible and irreversible modes differ.