kertakoodit

Kertakoodit are temporary, single-use codes that services issue to authenticate a user or authorize an action. They are designed to minimize the risk of credential theft by requiring a code that is valid only for one login, transaction, or short time window.

Kertakoodit can be generated in several ways. Time-based one-time passwords use a shared secret and the current time to produce a code that typically expires after a short period, often 30 or 60 seconds. Event-based codes are generated in response to a specific event, such as pressing a button on a hardware token. Most codes are numeric and commonly consist of six to eight digits, though lengths may vary by system.

Common delivery methods include authenticator apps that generate codes on a user’s device, SMS or email messages that carry the code, and hardware tokens or security keys that display or reproduce a code. Users may also scan a QR code to configure their device with the appropriate secret key for generating future codes. Standalone services, such as banks or online platforms, frequently combine kertakoodit with a username and password as part of two-factor authentication.

Standards and implementations exist to promote interoperability. The HOTP and TOTP methods, developed under the OATH project, specify how one-time codes should be produced and verified. TOTP is defined in RFC 6238, while HOTP is described in RFC 4226.

Security considerations include the risk of phishing, SIM-swapping when codes are delivered by SMS, and the potential for code reuse if not properly invalidated. Kertakoodit are a common layer of defense but are most effective when combined with strong authentication practices and user awareness.