Non Repudiation is your virtual John Hancock. It's a way of virtually stamping any data or document with "I am who I say I am". Only way to break this would be if the private key owners' private key became compromised. Which at that point you got bigger problems than Non Repudiation.

Password spraying is a type of brute-force attack in which a malicious actor uses a single password against targeted user accounts before moving on to attempt a second password, and so on. This technique allows the actor to remain undetected by avoiding rapid or frequent account lockouts. https://us-cert.cisa.gov/ncas/current-activity/2019/08/08/acsc-releases-advisory-password-spraying-attacks#:~:text=Password%20spraying%20is%20a%20type,rapid%20or%20frequent%20account%20lockouts.