February 24, 2019

316 words 2 mins read



Two-factor authentication on the command line

repo name rsc/2fa
repo link https://github.com/rsc/2fa
language Go
size (curr.) 11 kB
stars (curr.) 1018
created 2017-11-22
license BSD 3-Clause “New” or “Revised” License

2fa is a two-factor authentication agent.


go get -u rsc.io/2fa

2fa -add [-7] [-8] [-hotp] name
2fa -list
2fa name

2fa -add name adds a new key to the 2fa keychain with the given name. It prints a prompt to standard error and reads a two-factor key from standard input. Two-factor keys are short case-insensitive strings of letters A-Z and digits 2-7.

By default the new key generates time-based (TOTP) authentication codes; the -hotp flag makes the new key generate counter-based (HOTP) codes instead.

By default the new key generates 6-digit codes; the -7 and -8 flags select 7- and 8-digit codes instead.

2fa -list lists the names of all the keys in the keychain.

2fa name prints a two-factor authentication code from the key with the given name. If -clip is specified, 2fa also copies to the code to the system clipboard.

With no arguments, 2fa prints two-factor authentication codes from all known time-based keys.

The default time-based authentication codes are derived from a hash of the key and the current time, so it is important that the system clock have at least one-minute accuracy.

The keychain is stored unencrypted in the text file $HOME/.2fa.


During GitHub 2FA setup, at the “Scan this barcode with your app” step, click the “enter this text code instead” link. A window pops up showing “your two-factor secret,” a short string of letters and digits.

Add it to 2fa under the name github, typing the secret at the prompt:

$ 2fa -add github
2fa key for github: nzxxiidbebvwk6jb

Then whenever GitHub prompts for a 2FA code, run 2fa to obtain one:

$ 2fa github

Or to type less:

$ 2fa
268346	github
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