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2024-01-09 14:57:00 つかさの投稿 kyuizu@fedibird.com

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あと otpauth uri で桁数は指定されてるのでユーザーが気にする必要がないところでもある

TOTPがベースにしてるHOTPで6桁か8桁にしてね、7桁は脆弱だよって言ってるので大体桁数の指定がされてるもんだと思っていいよ

2024-01-09 14:22:50 zundaの投稿 zundan@mastodon.zunda.ninja

RFC 6238にはTOTPの桁数は規定されていないし参考の実装は8桁を生成しているように見える🤔

TOTP: Time-Based One-Time Password Algorithm
https://datatracker.ietf.org/doc/html/rfc6238

RFC 6238: TOTP: Time-Based One-Time Password Algorithm

RECOMMENDだから必ずそうとは限らないけど大体猶予を設けてるわね

This limit can be set both forward and backward from the calculated time step on receipt of the OTP value. If the time step is 30 seconds as recommended, and the validator is set to only accept two time steps backward, then the maximum elapsed time drift would be around 89 seconds, i.e., 29 seconds in the calculated time step and 60 seconds for two backward time steps.

This would mean the validator could perform a validation against the current time and then two further validations for each backward step (for a total of 3 validations). Upon successful validation, the validation server can record the detected clock drift for the token in terms of the number of time steps. When a new OTP is received after this step, the validator can validate the OTP with the current timestamp adjusted with the recorded number of time-step clock drifts for the token.

RFC 6238: TOTP: Time-Based One-Time Password Algorithm https://www.rfc-editor.org/rfc/rfc6238#section-6

RFC 6238: TOTP: Time-Based One-Time Password Algorithm
2024-01-09 14:10:23 kgtkrの投稿 me@mstdn.kgtkr.net

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