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Even after using Linux for years, you would always learn something new everyday. In this short article, I would talk about how SSH public key authentication could bypass security policy.

Let's start with pluggable authentication module (PAM). By using Linux PAM, the system could use modules to enhance the security of a system. For example, PAM could setup security policy that a password has to meet certain length and complexity. Another use case of the PAM …

2FA or two factor authentication is a mechanism of using another means of user authentication besides solely rely on password. 2FA or MFA (multiple factor authentication) would greatly increase the security. These are the common 2FA deployed in many internet web sites:

• One time password send over E-mail or SMS
• TOTP (Time-based One-Time Password algorithm)
• U2F (Universal 2nd Factor)
• WebAuthn (FIDO2 Web Authentication)

Now, most popular social media web sites and e-commerce sites had already supported at least one or multiple 2FA …