![]() Instead they assume the standard settings and generate tokens based on that, giving wrong tokens, no error messages and a bad user experience. My investigations show that many common mobile authenticator apps accept QR codes for hash algorithms, periods and number of digits they don’t support. Varying the number of digits is not mentioned in the TOTP standard apart from in the Java reference implementation, but it’s mentioned as an extension in the underlying HMAC-Based One-Time Password Algorithm (HOTP) standard ( RFC 4226) in Appendix E.1:Ī simple enhancement in terms of security would be to extract more digits from the HMAC-SHA-1 value.įor instance, calculating the HOTP value modulo 10^8 to build an 8-digit HOTP value would reduce the probability of success of the adversary from sv/10^6 to sv/10^8. The digits parameter may have the values 6 or 8, and determines how long of a one-time passcode to display to the user. The HMAC-SHA-1 hash function is the default but HMAC-SHA-256 and HMAC-SHA-512 are also allowed. The QR code encodes text on the so called Key URI format as per a Google Authenticator wiki article: TOTP standard recommends a default time-step size of 30 seconds. The de-facto standard is to transfer TOTP parameters including the secret (key) using a QR code. Thanks, git log -S Conclusion -walk-reflogs -patch! I got the idea for this blog post and now I’ve finally executed it and compared eight different TOTP apps for the two mobile platforms:ĮDIT: This section except for the last paragraph was accidentally deleted before publication and was restored two hours later. In October 2017 when I evaluated HashiCorp Vault for generating and storing TOTP secrets for a system at work I realized that the Android version and iOS version of Google Authenticator differed a lot when it comes to which modes are supported. The method is called Time-Based One-Time Password Algorithm (TOTP) and is standardized in RFC 6238. You probably use an “authenticator app” such as Google Authenticator to enable two-step verification (sometimes called two-factor authentication, 2FA, or multi-factor authentication, MFA) for an online account. See more details in Checking Out.Many Common Mobile Authenticator Apps Accept QR Codes for Modes They Don't Support You can checkout the project's source code from the Git repository.
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