authelia/docs/configuration/one-time-password.md

layout	title	parent	nav_order
default	Time-based One-Time Password	Configuration	16

Time-based One-Time Password

The OTP method Authelia uses is the Time-Based One-Time Password Algorithm (TOTP) RFC6238 which is an extension of HMAC-Based One-Time Password Algorithm (HOTP) RFC4226. You have the option to tune the settings of theTOTP generation, and you can see a full example of TOTP configuration below, as well as sections describing them.

Configuration

totp:
  disable: false
  issuer: authelia.com
  algorithm: sha1
  digits: 6
  period: 30
  skew: 1
  secret_size: 32

Options

disable

type: boolean {: .label .label-config .label-purple } default: false {: .label .label-config .label-blue } required: no {: .label .label-config .label-green }

This disables One-Time Password (TOTP) if set to true.

issuer

type: string {: .label .label-config .label-purple } default: Authelia {: .label .label-config .label-blue } required: no {: .label .label-config .label-green }

Applications generating one-time passwords usually display an issuer to differentiate applications registered by the user.

Authelia allows customisation of the issuer to differentiate the entry created by Authelia from others.

algorithm

type: string {: .label .label-config .label-purple } default: sha1 {: .label .label-config .label-blue } required: no {: .label .label-config .label-green }

Important Note: Many TOTP applications do not support this option. It is strongly advised you find out which applications your users use and test them before changing this option. It is insufficient to test that the application can add the key, it must also authenticate with Authelia as some applications silently ignore these options. Bitwarden is the only one that has been tested at this time. If you'd like to contribute to documenting support for this option please see Issue 2650.

The algorithm used for the TOTP key.

Possible Values (case-insensitive):

• sha1
• sha256
• sha512

Changing this value only affects newly registered TOTP keys. See the Registration section for more information.

digits

type: integer {: .label .label-config .label-purple } default: 6 {: .label .label-config .label-blue } required: no {: .label .label-config .label-green }

Important Note: Some TOTP applications do not support this option. It is strongly advised you find out which applications your users use and test them before changing this option. It is insufficient to test that the application can add the key, it must also authenticate with Authelia as some applications silently ignore these options. Bitwarden is the only one that has been tested at this time. If you'd like to contribute to documenting support for this option please see Issue 2650.

The number of digits a user needs to input to perform authentication. It's generally not recommended for this to be altered as many TOTP applications do not support anything other than 6. What's worse is some TOTP applications allow you to add the key, but do not use the correct number of digits specified by the key.

The valid values are 6 or 8.

Changing this value only affects newly registered TOTP keys. See the Registration section for more information.

period

type: integer {: .label .label-config .label-purple } default: 30 {: .label .label-config .label-blue } required: no {: .label .label-config .label-green }

The period of time in seconds between key rotations or the time element of TOTP. Please see the input validation section for how this option and the skew option interact with each other.

It is recommended to keep this value set to 30, the minimum is 15.

Changing this value only affects newly registered TOTP keys. See the Registration section for more information.

skew

type: integer {: .label .label-config .label-purple } default: 1 {: .label .label-config .label-blue } required: no {: .label .label-config .label-green }

The number of one time passwords either side of the current valid one time password that should also be considered valid. The default of 1 results in 3 one time passwords valid. A setting of 2 would result in 5. With the default period of 30 this would result in 90 and 150 seconds of valid one time passwords respectively. Please see the input validation section for how this option and the period option interact with each other.

Changing this value affects all TOTP validations, not just newly registered ones.

secret_size

type: integer {: .label .label-config .label-purple } default: 32 {: .label .label-config .label-blue } required: no {: .label .label-config .label-green }

The length in bytes of generated shared secrets. The minimum is 20 (or 160 bits), and the default is 32 (or 256 bits). In most use cases 32 is sufficient. Though some authenticators may have issues with more than the minimum. Our minimum is the recommended value in RFC4226, though technically according to the specification 16 bytes (or 128 bits) is the minimum.

Registration

When users register their TOTP device for the first time, the current issuer, algorithm, and period are used to generate the TOTP link and QR code. These values are saved to the database for future validations.

This means if the configuration options are changed, users will not need to regenerate their keys. This functionality takes effect from 4.33.0 onwards, previously the effect was the keys would just fail to validate. If you'd like to force users to register a new device, you can delete the old device for a particular user by using the authelia storage totp delete <username> command regardless of if you change the settings or not.

Input Validation

The period and skew configuration parameters affect each other. The default values are a period of 30 and a skew of 1. It is highly recommended you do not change these unless you wish to set skew to 0.

These options affect security by changing the length of time a one-time password is valid for. The formula to calculate the effective validity period is period + (period * skew * 2). For example period 30 and skew 1 would result in 90 seconds of validity, and period 30 and skew 2 would result in 150 seconds of validity.

System time accuracy

It's important to note that if the system time is not accurate enough then clients will seemingly not generate valid passwords for TOTP. Conversely this is the same when the client time is not accurate enough. This is due to the Time-based One Time Passwords being time-based.

Authelia by default checks the system time against an NTP server on startup. This helps to prevent a time synchronization issue on the server being an issue. There is however no effective and reliable way to check the clients.

Encryption

The TOTP secret is encrypted in the database in version 4.33.0 and above. This is so a user having access to only the database cannot easily compromise your two-factor authentication method.

This may be inconvenient for some users who wish to export TOTP keys from Authelia to other services. As such there is a command specifically for exporting TOTP configurations from the database. These commands require the configuration or at least a minimal configuration that has the storage backend connection details and the encryption key.

Export in Key URI Format:

$ authelia storage totp export --format uri

Export as CSV:

$ authelia storage totp export --format csv

Help:

$ authelia storage totp export --help