[sdevlin]

Where are you getting that number?

[tptacek]

The Noise framework documentation. I know there's "a" number for GCM, but I always forget what it is, so I keep going back to Noise.

[sdevlin]

I don't think their bound is related to nonce-management issues. From the documentation:

> The GCM security limit is 2^56 bytes because:

> This is 2^52 AES blocks (each block is 16 bytes). The limit is based on the risk of birthday collisions being used to rule out plaintext guesses. The probability an attacker could rule out a random guess on a 2^56 byte plaintext is less than 1 in 1 million (roughly (2^52 * 2^52) / 2^128).

[tptacek]

Yep. I'm wrong. I'll stop sourcing that number from Noise. :)

(Clarified offline: I'm thinking of the 32 bit counter in GCM, which will wrap in tens of gigabytes worth of bytes under a single nonce. Not a TLS issue, a concern for custom protocols.)