Why is the email hashed and then encrypted? Isn’t encryption enough?
This is a privacy-by-design decision:
- Even though metadata is encrypted with XSalsa20-Poly1305 (very secure), the email is first hashed with SHA-256 before being encrypted.
- This double protection ensures that even if encryption is broken in the future (e.g. via quantum computing), the original email is still not directly exposed.
- It also allows the user to verify ownership by hashing their own email and comparing it with the decrypted value, without revealing it in cleartext.
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