Einmalcodes

EinmalCodes is a term used to describe one-time use authentication codes, commonly used as a second factor or as a primary credential in access-control systems. They are designed to be valid for a single login or transaction and are typically six to eight digits long. Codes may be delivered or generated by various means, including authenticator apps, hardware tokens, SMS, or email, and are often configured on a user’s device or a physical token.

Most EinmalCodes rely on a shared secret between the client and the authentication server. Time-based one-time passwords (TOTP) compute the code from the current time and the secret, while counter-based HOTP uses a moving factor such as login attempts. Verification on the server checks the code against expected values and rejects it after expiration or reuse. In multi-factor setups, a valid code is often combined with a password or biometric factor.

Delivery methods and interoperability vary. Authenticator apps implement TOTP/HOTP per standards developed by the Open AuTHentication (OATH) initiative, with RFC 4226 (HOTP) and RFC 6238 (TOTP) as common references. Hardware tokens, FIDO-style devices, and certain push-based approaches provide additional options. QR codes are frequently used to configure apps or devices quickly.

Security considerations are central to EinmalCodes. They reduce risks associated with static passwords but are not immune to interception or phishing, especially when delivered via SMS. Phishing-resistant methods, device binding, proper server-side protections, and rate limiting improve security. Codes should be short-lived and revocable when devices are lost or compromised.

Usage and adoption span online banking, enterprise VPNs, consumer web services, and government applications. EinmalCodes remain a core component of many multifactor authentication strategies and continue to evolve with new hardware and protocol innovations.