Since the server is responsible for generating the tokens, the first problem we have is sharing the secret key with the client. It’s a token that’s shared between a server and client so we can be sure the client has somehow been granted access. The secret key is probably something you’ve encountered in one form or another on some corner of the internet. The HOTP algorithm depends on two pieces of information in order to produce a token we can reliably use – a moving factor and a secret key. Hmac-based One-Time Password algorithm (HOTP) The answer lies in the HMAC-based One-Time Password algorithm. How can we ensure we only ever generate a unique token? You may already have spotted the giant bottleneck in implementing a robust OTP system. Regardless of how it’s implemented, such a password should only ever be valid for a single use case, then gets disregarded. One Time PasswordĪ one-time password is a kind of token (a code or word) that can only be used once. This is the traditional method of logging in that you’re probably used to.īefore we get lost in a whole mess of new words, let’s break down some of the important vocabulary that will make it much easier to discuss upcoming concepts. Single-factor authentication refers to the kind of login that only requires a username (or email) and password. Two-factor authentication (often abbreviated TFA or 2FA) is a method of authenticating clients that involves ‘two factors’ when verifying a user – a password and something the user can physically access – like a fingerprint or a random SMS code (or even better, a one-time password!). This can be a particular problem if the attacker breaches a large authentication database.There’s probably no better time to integrate two-factor authentication into your a than today. An attacker with access to this shared secret could generate new, valid TOTP codes at will. TOTP credentials are also based on a shared secret known to both the client and the server, creating multiple locations from which a secret can be stolen. Due to the short window in which TOTP codes are valid, attackers must proxy the credentials in real time. However, users must enter TOTP codes into an authentication page, which creates the potential for phishing attacks. Unlike passwords, TOTP codes are single-use, so a compromised credential is only valid for a limited time. But a single leap second does not cause the integer part of Unix time to decrease, and C T is non-decreasing as well so long as T X is a multiple of one second. When a leap second is inserted into UTC, Unix time repeats one second. T X is the length of one time duration (e.g.T 0 is the epoch as specified in seconds since the Unix epoch (e.g.T is the current time in seconds since a particular epoch,.C T is the count of the number of durations T X between T 0 and T,.TOTP uses the HOTP algorithm, replacing the counter with a non-decreasing value based on the current time:Ĭ T = ⌊ T − T 0 T X ⌋, Some authenticators allow values that should have been generated before or after the current time in order to account for slight clock skews, network latency and user delays. T X, an interval which will be used to calculate the value of the counter C T (default is 30 seconds).īoth the authenticator and the authenticatee compute the TOTP value, then the authenticator checks whether the TOTP value supplied by the authenticatee matches the locally generated TOTP value.T 0, the Unix time from which to start counting time steps (default is 0),.To establish TOTP authentication, the authenticatee and authenticator must pre-establish both the HOTP parameters and the following TOTP parameters: In May 2011, TOTP officially became RFC 6238. This version incorporates all the feedback and commentary that the authors received from the technical community based on the prior versions submitted to the IETF. In 2008, OATH submitted a draft version of the specification to the IETF. It complements the event-based one-time standard HOTP, and it offers end user organizations and enterprises more choice in selecting technologies that best fit their application requirements and security guidelines. Through the collaboration of several OATH members, a TOTP draft was developed in order to create an industry-backed standard. TOTP is the cornerstone of Initiative for Open Authentication (OATH), and is used in a number of two-factor authentication (2FA) systems. As an extension of the HMAC-based one-time password algorithm (HOTP), it has been adopted as Internet Engineering Task Force (IETF) standard RFC 6238. Time-based one-time password ( TOTP) is a computer algorithm that generates a one-time password (OTP) using the current time as a source of uniqueness.
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