Migrating from Classical Cryptography

If you’re currently using Ed25519 for signatures or X25519 for key exchange, @brivora/crypto provides a smooth upgrade path to hybrid PQC.

Step 1: Upgrade existing Ed25519 keys

import { crypto } from '@brivora/crypto';

const upgraded = await crypto.upgradeKey({
  publicKey: existingEd25519PublicKey,
  secretKey: existingEd25519SecretKey,
});

// upgraded.identity -- new hybrid PQC identity
// upgraded.migration -- signed proof linking old key to new key

Step 2: Verify the upgrade

const { valid } = await crypto.verify(upgraded.migration, oldPublicKey);
// valid === true -- the upgrade is cryptographically linked to the old key

Step 3: Distribute the migration proof

Publish the migration proof so that anyone who trusted your old Ed25519 key can verify that your new hybrid PQC key is legitimate. The proof is signed by both the old and new keys.

Migration strategy

Phase	Action	Duration
1. Upgrade	Generate hybrid identities for all existing keys	Hours
2. Dual mode	Accept both old Ed25519 and new hybrid signatures	Weeks-months
3. Cutover	Require hybrid signatures, deprecate classical-only	When ready

Backward compatibility

During migration, hybrid mode ensures:

• Old systems can still verify Ed25519 signatures from hybrid keys
• New systems get full PQC protection
• No breaking changes to existing verification flows