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REDDIT

Collision Resistance of HMACs

F
Feb 4, 2026 · 17:41

Hi everyone. I am studying HMACs and I just wanted to double-check: the collision resistance of an HMAC checksum is roughly half of the bit size of the checksum itself, right?

So for example HMAC-SHA-256 has a collision resistance of 128 bits due to the birthday paradox.

Please let me know if there is anything wrong with my analysis. I thank all for all advances in response!