.\" Copyright (c) 2022, 2023 Omar Polo <op@omarpolo.com>
.\"
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.Dd May 27, 2023
.Dt TOTP 1
.Os
.Sh NAME
.Nm totp
.Nd time-based one time password generator
.Sh SYNOPSIS
.Nm
.No < Ns Ar secret
.Sh DESCRIPTION
.Nm
is a time-based one time password generator
.Pq TOTP .
It reads a secret from standard input and prints the generated password,
a numeric code, to standard output.
The secret is usually provided by the authenticator
.Pq for e.g.\& a website
and is either a base32-encoded string or a
.Sq otpauth://
URI.
Blanks in the secret string are ignored, but only one line is read.
.Pp
.Nm
uses a period of 30 seconds, HMAC-SHA1 and generates six digits long
codes, unless the URL specifies otherwise.
.Sh EXIT STATUS
.Ex -std
.Sh EXAMPLES
.Nm
is meant to be used with
.Xr plass 1
or similar application: the secret is stored safely in the password
store and then given to
.Nm
using a pipe:
.Bd -literal -offset indent
$ plass cat 2fa/codeberg/op | totp
722524
.Ed
.Sh SEE ALSO
.Xr plass 1
.Sh STANDARDS
.Nm
follows the algorithm outlined in RFC 6238
.Dq TOTP: Time-Based One-Time Password Algorithm
and uses the base32 encoding as defined in RFC 3548
.Dq The Base16, Base32, and Base64 Data Encodings .
.Sq otpauth://
URIs are parsed as per the
.Dq Key URI Format
proposed by Google Authenticator.
.Sh AUTHORS
.An -nosplit
The
.Nm
utility was written by
.An Omar Polo Aq Mt op@omarpolo.com .