What is a Hardware Security Key?

Last updated May 28, 2019

In brief, a Hardware Security Key is a physical device that prevents unauthorized access to accounts by using public key cryptography.

Before describing how a hardware security key works and what it consists of, the question that needs to be answered first is: Why use it and why is it better than using a password (and other “second factors”)?

Firstly, let’s look at the “public key cryptography” part of the description. One of the problems with passwords is that they are in essence “symmetric” keys. This means the actual password has to be typed (or copied from a password manager) into a password form field of a browser (or application). From the form field it is then transferred to a server. The problem is that the OS, browser or even server is not necessarily secure - as many people who have been the victims of phishing attacks and ransom ware can testify. There are many opportunities for a hacker to obtain a copy of this password by using key loggers, browser plugins, posing as the real server or even hacking the server itself. (Also have a look at our blog post on Webauthn).

In contrast, a hardware security key uses a private key to digitally sign a random chunk of data to prove to the server that it has ownership of the private key. The server verifies this signature by using the public key. The private key is never transferred out of the security key so there is no opportunity for the hacker to obtain the private key.

From a hardware point of view, a well designed hardware security key like the MIRkey is in essence a simplified form of a hardware security module. This means the private keys are protected by using a secure element in secure silicon and the cryptographic operations are performed in a secure environment - no other software is allowed to execute in the secure environment. The only way to obtain the private key is to get physical access to the security key and even then it is very difficult, costly and time consuming to retrieve the private key from the device. This provides you with ample time to:

  • Notice that the key is missing and

  • de-register the security key before your account can be compromised.

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