This can be a particular problem if the attacker breaches a large authentication database. 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. The code is generated using HMAC (sharedSecret, timestamp), where the timestamp changes every 30 seconds. To authenticate using TOTP (time-based one-time password) the user enters a 6-8 digit code that changes every 30 seconds. 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. OATH is an organization that specifies two open authentication standards: TOTP and HOTP. 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. ![]() HOTPs are generated by combining a secret key or seed with a counter and using a one-way cryptographic hash function to produce 160-bit code, which is then shortened to a six or eight-digit OTP.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. The counter on the token is generated when the button is pressed, while the counter on the server is incremented only when an OTP is successfully validated. The counter is stored in the token, on the server. Moving factor: The moving factor in an event-based OTP is the counter (which counts the number of OTPs generated).Secret key or seed: This is only known by the user’s token and the server that validates submitted OTP codes.HOTPs depends on two pieces of information: The secret key is then stored by the token and the server and never shared again. This key, sometimes known as “the seed”, is a value that the OTP token and the server exchange only once during the initialization of the token. It verifies a user’s identity by requiring them to enter a unique code in addition to their password.Īt the very heart of the HOTP is a secret key. Hash-based one-time passwords (HOTP) are generated using a cryptographic hash function.
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