PBKDF2 iterations reduced 10x - weakens anonymity against brute-force attacks

[amaydixit11]

Issue

The anonymization system intentionally reduced PBKDF2 iterations for "speed":

• generateAnonymousIdentity in lib/anonymization.ts:35: reduced from 100,000 to 10,000 iterations
• Double hashing in lib/supabase-auth.ts:72: reduced from 50,000 to 5,000 iterations

Why this matters

The anonymization system's security model depends on the PBKDF2 hash being computationally infeasible to brute-force. If an attacker obtains the database (which contains verification_hash and salt), they can attempt to reverse the hash by trying common email patterns:

• student@iitbh.ac.in
• professor@iitbh.ac.in
• Common name patterns at IIT Bhilai

At 10,000 iterations, this is 10x faster to brute-force than the originally intended 100,000. Combined with the small email space (all IIT Bhilai students), a targeted attack could deanonymize users.

Fix

1. Restore 100,000 iterations for generateAnonymousIdentity
2. Restore 50,000 iterations for the double-hash verification
3. If speed is a concern, consider client-server split: do the slow hash server-side only