![]() A one-time password in HOTP can stay valid until it’s used to authenticate, providing plenty of time for potential hackers to carry out an attack. ![]() In TOTP, a new password is generated every 30 seconds while in HOTP, a new password is generated only after it has been used. It’s noteworthy that TOTPs are more secure than HOTPs. The robustness of a hash function is that you cannot reproduce the original parameters that went into it if you only have the output. The process involves a hash function that takes an arbitrary length input and produces a short, fixed-length string of characters. ![]() The TOTP algorithm is technically a variation of the HMAC-Based One-Time Password (HOTP) algorithm, where the counter is replaced with the current time value. Time-based one-time passwords use the current time and a shared secret to generate a unique password. TOTPs are usually enabled via authentication apps and the generated passwords are only valid for a certain period of time, usually 30 to 60 seconds. This method is commonly used for two-factor authentication (2FA) to provide an additional layer of security. It is a temporary passcode, generated by an algorithm, that uses the current time of day as one of its factors for authentication. All Microcosm OTP tokens are OATH-compliant.A time-based one-time password (TOTP) is a type of one-time password that uses the current time as a source of uniqueness. The HOTP and TOTP standards are produced by OATH, the Initiative for Open Authentication. Cards can be a more convenient option as they can be stored with other cards in a wallet or purse, or in the back of a mobile phone case. Traditional key fob OTP tokens are getting smaller and Microcosm has now introduced the OTP Card - a credit card sized OTP token with EPD display. There is also more choice of form-factor with TOTP tokens. Importantly, the validating server must be able to cope with potential for time-drift with TOTP tokens in order to minimise any impact on users. ChoiceĬhoosing between HOTP and TOTP purely from a security perspective clearly favours TOTP. In contrast, in TOTP there is only one valid OTP at any given time - the one generated from the current UNIX time. Importantly though, the larger the window the greater the chance of an adversary guessing one of the accepted OTPs through a brute-force attack. The larger the validation window the less likely the chance of needing to re-sync the token with the server, which is inconvenient for the user. So clearly in HOTP there is a trade-off to make. If the token counter is outside of the range allowed by the server, the validation fails and the token must be re-synchronised. This is range is referred to as the validation window. Specifically, they will accept an OTP that is generated by a counter that is within a set number of increments from the previous counter value stored on the server. For this reason, HOTP validating servers accept a range of OTPs. This is because the button on the token can be pressed, thus incrementing the counter on the token, without the resulting OTP being submitted to the validating server. In HOTP there are a number of valid "next OTP" codes. Comparisonīoth OTP schemes offer single-use codes but the key difference is that in HOTP a given OTP is valid until it is used, or until a subsequent OTP is used. This means that each OTP is valid for the duration of the timestep. TOTP uses time in increments called the timestep, which is usually 30 or 60 seconds. Time-based OTP (TOTP for short), is based on HOTP but where the moving factor is time instead of the counter. This produces a 160-bit value which is then reduced down to the 6 (or 8) decimal digits displayed by the token. HOTP uses the SHA-1 hash function in the HMAC. To calculate an OTP the token feeds the counter into the HMAC algorithm using the token seed as the key. The counter in the token increments when the button on the token is pressed, while the counter on the server is incremented only when an OTP is successfully validated. The counter is stored in the token and on the server. The second piece of information is the moving factor which, in event-based OTP, is a counter. The first is the secret key, called the "seed", which is known only by the token and the server that validates submitted OTP codes. View our range of OTP cards and tokens HOTP: Event-based One-Time PasswordĮvent-based OTP (also called HOTP meaning HMAC-based One-Time Password) is the original One-Time Password algorithm and relies on two pieces of information. The security of OTP is based on fact that the codes are constantly changing and that they are single-use, hence the name. In both HOTP and TOTP the token (ie, the OTP generator) generates a numeric code, usually 6 or 8 digits. HOTP and TOTP are the two main standards for One-Time Password but what do they mean from a security perspective, and why would you choose one over the other?
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