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Circumvent Exact Online 2FA to avoid entering PIN-code every ten minutes

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Summary

This note presents a number of easy steps to circumvent the entry every ten minutes of a 2FA PIN-code on Exact Online when used with Invantive Control for Excel and other interactive Invantive apps.

The steps can be used with or without Invantive Authenticator.

This poses a limited additional security risk since connected apps can already work without a PIN-code after initial entry, using a refresh token.

Exact Online 2FA and Invantive Control

Starting May 25, Exact Online is requiring the use of 2FA for all users. When properly implemented, you can achieve strong authentication with 2FA on Exact Online. Strong authentication is required by law for reasons such as irreversible financial transactions and data traceable to individuals. For a proper implementation, you must isolate the storage of the secret used to generate the 2FA PIN-code from the your normal working environment. Generating the 2FA PIN-codes on a mobile phone achieves this largely. This is similar to the Vasco hardware tokens previously used by Exact Online, but these came with a charge of EUR 5 per hardware token per month.

There are many apps available on Exact Online. Some apps apply the so-called "Implicit Grant" in adherence to the OAuth recommendations. This typically holds for apps running on devices untrusted by the owner of the application, such as Invantive Control on your PC or an iPhone app.

However, at this moment the use of Implicit Grant also requires you to re-enter a new PIN-code every ten minutes. For Invantive and other app suppliers there is no supported way of avoiding this hassle during your use of our applications. This note presents a number of easy steps to circumvent this problem.

Jump directly to the steps to execute or continue reading the background.

Additional security recommendations for Exact Online can be found in another note.

How 2FA Works

The implementation of Exact Online is based upon an industry standard for Time-based One-Time Passwords (TOTP). During the TOTP registration, your mobile device or chosen program exchange a shared secret. This shared secret is contained in the QR-code on the TOTP registration page:

exact-online-qr-scan

The QR-code next to the red (1) has been completely blurred since a QR-code is extremely insensitive to transmission errors. Truly a miraculous algorithm made by mathematicians.

Using this QR-code, the Exact Online app shares a secret like the following with your phone:

otpauth://totp/ExactOnline%3aMYLOGINCODE?secret=ALONGTEXTOFDIGITSANDCHARACTERS&issuer=Exact%20Online

This secret can also be seen when you click on "Can't scan the QR-code" at the red (2) below the QR-code:

exact-online-shared-secret

An algorithm takes the pre-shared secret and the current world time rounded down to 30 second precision and calculates the PIN-code. This PIN-code calculation takes place at both ends of the communication: at the side of the user and at the side of Exact Online. A user is allowed access when both entries match.

Such a pre-shared secret can also be used with Invantive Authenticator.

It is either very hard or impossible to derive the pre-shared secret even with a large number of PIN-codes and associated timestamps available.

Alternative implementations found in the cloud market do not share the secret with you, but put the secret keys on a closed environment to which the user has no access. This closed environment upon user request communicates the PIN-code to you using a separate channel such as SMS (preferably, such as Dropbox) or mail (well... sometimes an attack vector).

Circumvent Exact Online 2FA for apps

New releases of Invantive applications for running on your devices support two additional approaches to log in on Exact Online:

Using a refresh token, client secret, client ID and redirect URI.

Using the user, password and pre-shared TOTP secret.

Log in using Refresh Token

Although all our products support for use on your devices support both approaches, we recommend the use of a refresh token with server-oriented products like Invantive Data Replicator or Invantive Data Hub. These products typically run unattended on a server using a dedicated Exact Online account. Contact our support to upgrade and together generate a client ID, client secret and refresh token using the pre-authentication site cloud.invantive.com.

Please store your credentials carefully, since they allow access to your Exact Online data with the same privileges as the user. Also, subsequent assistance is only offered based upon a consulting rate. As an alternative, you can generate a new refresh token using the documentation.

Server products such as Invantive Data Access Point have come to support Exact Online 2FA too, both for normal use as well as with Ajax, but they require the use of your own client ID and secret. If you base an application on Invantive products, please ALWAYS make sure you either DON'T persistently store refresh token or store them encrypted according to the law.

Log in interactively using TOTP Secret

You should perform the following steps to log in to Invantive Control and other interactive apps using the credentials of your user account:

Re-generate the QR-code and click on the red (2) as shown above or extract the secret key from the QR-code image otherwise using a trusted decryptor.

Store the TOTP secret key under lock & key and consider it part of your password.

Upon log in to Invantive Control, provide your user name (1), password (2) and secret TOTP key (3) in the login box:

exact-online-totp-secret-login

Note that the secret key can currently be stored unencrypted on your device in settings.xml. Therefor ensure application of other security measures such as using the device only inside a secured building or protect access to Windows by a log on code and password and hard disk encryption. We will improve this mechanism in a future release.

Note that Exact Online as far as known does not impose location-based access controls on all apps and interactive use. Store your credentials safely and use them only in trusted environments with trusted apps! Check that the apps you use are provided by suppliers located within your own legislation region (country or European Union as long as that still holds) or considered comparable with your legislation and in which law is actually enforced.