How long before a challenge is brute forced?

[lil5]

This good to know when creating lifetime for a challenge

[dagnelies]

So, just to be clear, the challenge is just a random value, in our case with 18 bytes / 144 bit of entropy by default.

If the attacker has eavesdropped an authentication payload, and wants to "repeat" the login using the same payload, hence the same challenge, he would have to send on average roughly 10^43 requests to your server ...that's a lot of zeroes.