![]() For example, one-time codes sent via email or SMS are, strictly speaking, 2-step verification, as getting those codes isn’t directly tied to something you have. The difference between two-factor authentication and 2-step verification is nuanced, as explained in this diagram. Two-factor authentication might also verify something you are: a biometric-such as your fingerprint or face-using a phone, computer, or external device. Some people also include one-time codes sent to your phone over SMS or by email as two-factor authentication as well but, strictly speaking, those are a form of 2-step verification, as I’ll discuss below. The something you have could be a number of different things: an OTP (one-time password, typically 6-8 digits) from your authenticator app or a key fob, a push verification done through your smartphone, or a USB security key you plug into your computer. There’s often some confusion on this term but, to put it simply, two-factor authentication verifies something you know-usually your username and password- along with either “something you have” or “something you are”. Multi-factor 2FA / two-factor authentication / second-factor authentication In this blog, I will attempt to clarify the terms you need to know and explain how they relate to each other. However, the terminology around these things often appears intentionally confusing. If a time delay is required, a VerificationWindow object can be provided that describes the acceptable range of values to check.Web Authentication, security keys, one-time passwords, and the like have been top of mind as increased phishing attacks and rapid explosion of remote work has made stronger security controls critical. Simply omitting the optional parameter will cause this default behavior. The default is that no delay will be accepted and the code must match the current code in order to be considered a match. The actual step where the match was found will be reported in the aforementioned output parameter. This parameter allows you to define the window of steps that are considered acceptable. The VerifyTotp method takes an optional VerificationWindow parameter. The exact text in the RFC is "We RECOMMEND that at most one time step is allowed as the network delay." RFC 6238 Section 5.2 defines the recommended conditions for accepting a TOTP validation code. This library will only go so far as to determine that there was a valid code provided given the current time and the key, not that it was truly used one time as this library has no persistence. It is up to the consumer of this library to ensure that only one match for a given time step window is actually accepted. The output parameter reports the specific time window where the match occured for persistance comparison in future verification attempts. RFC 6238 Section 5.2 states that a code must only be accepted once. ![]() This is provided so that the caller of the function can persist/check that the code has only been validated once. ![]() There is an output long called timeWindowUsed. ![]() If the overload that doesn't take a timestamp is called, DateTime.UtcNow will be used as the comperand. Public bool VerifyTotp ( string totp, out long timeWindowUsed, VerificationWindow window = null ) public bool VerifyTotp ( DateTime timestamp, string totp, out long timeWindowUsed, VerificationWindow window = null ) ![]()
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