3 Two-factor authentication
So, if a password isn’t secure enough, perhaps having two pieces of information is more secure? This is known as two-factor authentication and you’ve almost certainly used it without realising.
When you take money out of an ATM you have to give the bank two pieces of information – the first is the data stored on your bank card, the second is the PIN. Individually, neither can access your account, but when brought together they allow you to withdraw money.
Some banks have given similar two-factor authentication to online banking customers – in this case accounts need to be unlocked with the combination of a password and a four or six digit number generated on a hardware security token. If you use online banking and don’t have a hardware token it will be well worth finding out if your bank offers them to customers, and if they do not, consider switching to a more secure banking service.
Hardware security tokens
These devices contain a clock and a number generator which creates a new one-time password every minute or so. The bank synchronises the token with a master computer before issuing it to customers so the token and the master computer generate new passwords in time with one another. When the user is asked to enter the one-time password into their browser, they press a button on the token and enter the four or six digit number shown on the screen. The master computer will have also generated the same number. The two values are compared, and if they match, the user is allowed into their account.
Two-factor authentication on the web
A number of companies, including Apple, eBay, Google and Microsoft support two-factor authentication to improve the security for their web users. Rather than a single password, two-factor authentication requires the user to enter two pieces of information – their password and a changing value which is either sent by the website to their mobile phone, or generated by a companion application on the user’s own computer.
Depending on the site, it might be necessary to enter the two values every time (which is inconvenient), or after a period of inactivity, or it may be possible to tell the site that the computer which has already been authenticated should be trusted in future and a single password will be sufficient to allow you to use the site (although this raises a security weakness if the machine should be stolen).
Another place where you might have come across two-factor authentication is if you’ve ever connected to a virtual private network (VPN), which is a type of encrypted network connection. (You will cover VPNs in more detail in Week 5.)
The organisation that owns the network you are connecting to will give you a card or device, often called a VPN token, that can be used to generate a sequence of random characters. When you try to connect to the VPN, you will first be asked for your password (the secret based on something you know) and then will be challenged to provide some information from the VPN token (the secret based on something you have).