The mailbox previously trusted the client-supplied envelope ID and SentAt,
which enabled two attacks:
- replay via re-broadcast: a malicious relay could resubmit the same
ciphertext under multiple IDs, causing the recipient to receive the
same plaintext repeatedly;
- timestamp spoofing: senders could back-date or future-date messages
to bypass the 7-day TTL or fake chronology.
Store() now recomputes env.ID as hex(sha256(nonce||ct)[:16]) and
overwrites env.SentAt with time.Now().Unix(). Both values are mutated
on the envelope pointer so downstream gossipsub publishes agree on the
normalised form.
Also documents /relay/send as non-E2E — the endpoint seals with the
relay's own key, which breaks end-to-end authenticity. Clients wanting
real E2E should POST /relay/broadcast with a pre-sealed envelope.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
