![]() An example of this type of algorithm, credited to Leslie Lamport, uses a one-way function (call it f is a cryptographic hash function, which is generally the case, it is assumed to be a computationally intractable task. Some applications can be used to keep time-synchronized OTP, like Google Authenticator or a password manager.Įach new OTP may be created from the past OTPs used. An example of a time-synchronized OTP standard is Time-based One-Time Password (TOTP). This token may be a proprietary device, or a mobile phone or similar mobile device which runs software that is proprietary, freeware, or open-source. On these OTP systems, time is an important part of the password algorithm, since the generation of new passwords is based on the current time rather than, or in addition to, the previous password or a secret key. ![]() Inside the token is an accurate clock that has been synchronized with the clock on the proprietary authentication server. It might look like a small calculator or a keychain charm, with an LCD that shows a number that changes occasionally. Using a mathematical algorithm where the new password is based on a challenge (e.g., a random number chosen by the authentication server or transaction details) and/or a counter.Ī time-synchronized OTP is usually related to a piece of hardware called a security token (e.g., each user is given a personal token that generates a one-time password).Using a mathematical algorithm to generate a new password based on the previous password (OTPs are effectively a chain and must be used in a predefined order).Based on time-synchronization between the authentication server and the client providing the password (OTPs are valid only for a short period of time).Various approaches for the generation of OTPs include: Generation Ĭoncrete OTP algorithms vary greatly in their details. In some mathematical algorithm schemes, it is possible for the user to provide the server with a static key for use as an encryption key, by only sending a one-time password. Finally, in some systems, OTPs are printed on paper that the user is required to carry. Yet other systems generate OTPs on the server-side and send them to the user using an out-of-band channel such as SMS messaging. Other systems consist of software that runs on the user's mobile phone. Some systems use special electronic security tokens that the user carries and that generate OTPs and show them using a small display. There are also different ways to make the user aware of the next OTP to use. A number of OTP systems also aim to ensure that a session cannot easily be intercepted or impersonated without knowledge of unpredictable data created during the previous session, thus reducing the attack surface further. A second major advantage is that a user who uses the same (or similar) password for multiple systems, is not made vulnerable on all of them, if the password for one of these is gained by an attacker. This means that a potential intruder who manages to record an OTP that was already used to log into a service or to conduct a transaction will not be able to use it, since it will no longer be valid. The most important advantage addressed by OTPs is that, in contrast to static passwords, they are not vulnerable to replay attacks. Many systems that use OTPs do not securely implement them, and attackers can still learn the password through phishing attacks to impersonate the authorized user. ![]() On the downside, OTPs can be intercepted or rerouted, and hard tokens can get lost, damaged, or stolen. OTPs have been discussed as a possible replacement for, as well as an enhancer to, traditional passwords. This is necessary because otherwise, it would be easy to predict future OTPs by observing previous ones. OTP generation algorithms typically make use of pseudorandomness or randomness to generate a shared key or seed, and cryptographic hash functions, which can be used to derive a value but are hard to reverse and therefore difficult for an attacker to obtain the data that was used for the hash. OTPs avoid several shortcomings that are associated with traditional (static) password-based authentication a number of implementations also incorporate two-factor authentication by ensuring that the one-time password requires access to something a person has (such as a small keyring fob device with the OTP calculator built into it, or a smartcard or specific cellphone) as well as something a person knows (such as a PIN). MasterCard SecureCode uses OTAC to confirm a user's identity One time authorization code as used in Yammer's desktop clientĪ one-time password ( OTP), also known as a one-time PIN, one-time authorization code ( OTAC) or dynamic password, is a password that is valid for only one login session or transaction, on a computer system or other digital device.
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