Introduction to cyber security: stay safe online
Introduction to cyber security: stay safe online

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Introduction to cyber security: stay safe online

1.1 What happens when you enter a password?

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When a user connects to the server for the first time, they may be asked to create a password so they can get access to the services available on the server. In this case, the user types in a simple password. To keep things easy, we're using the very simple-- and very bad-- password "apple." Your own passwords should be much harder to guess. The user's password is sent over the network and is stored in a database on the server. At some later date, the user wants to access the server again. They're asked for their password, and type in "apple." The password is sent over the network and compared to the stored password-- also "apple"-- in the server's database. If the two match, they're given access.
Any data passing over a network can be stored or intercepted. It's very easy to copy data on a network, so an attacker could make their own copy of the password. Once they have that, they can then log into the server masquerading as the original user. A second problem is that the database itself might be stolen from the server by hackers-- or even a disgruntled employee. If this were to happen, all of the passwords belonging to all of the users could be misused.
To prevent passwords being stolen in transit, we use a secure network link between the user's computer and the server which hides data using strong cryptography. One type of secure link is called SSL, which you'll have used, perhaps without knowing it, when shopping online.
It's much harder to stop the server's database being stolen. But we can obscure passwords using a technique called hashing. Hashing is a mathematical technique that scrambles a password to produce a so-called hash. So when the user creates a password, server turns the password into a hash. And rather than storing the password in the database, we store the hash. So when the user logs in next time, they enter their password, which is sent over the network. The server creates a new hash from the password and compares it to the stored hash. If the two hashes match, then the user is allowed into the computer. Crucially, hashing only works one way. It's not possible to simply undo the hashing to recover the original password. Even if the database is stolen, the attackers only have the hashed passwords, rather than the passwords themselves. If the attackers want to find out the original passwords, they'll have to hash every possible password and compare them to the list of stored hashes. This is an enormously time-consuming process.
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When a user enters a password it is matched against the password stored by that website. If the passwords match, the user is granted access.

There are a couple of potential weaknesses with this approach that you can probably recognise:

  1. The password is transmitted as plaintext (what you see is exactly what you get; it isn’t hidden in any way) – it could be intercepted as it travels across the network.
  2. The password is stored as plaintext – an attack on the server could not only reveal the user’s password, but all the passwords for all the users of the system.

The first problem is usually overcome by encrypting the communication between the user and the server. The most common form of encryption is the SSL standard (Secure Socket Layer). You’ll recognise that SSL is being used when you see ‘https’ at the beginning of a web page address instead of ‘http’, and by a padlock symbol in your browser. (You’ll look at encryption and SSL more fully in Week 4.)

The second problem can also be solved using a technique called hashing. A hash is the result of processing plaintext to create a unique, fixed length identifier – you’ll find out more in Week 5. It cannot be used to reconstruct the original data – even if the hash falls into hostile hands. In this scheme, a hashing function is used to create a hash of a password, which is stored on the server – the password itself is discarded. When the user enters a password, this is sent over the network and hashed on the server using a copy of the same hashing function. The resulting hash is compared to the hash stored on the password server. Only if they match will the user be granted access. Some implementations of this scheme will hash the user’s password before sending it across the network to be compared with the hash stored on the server.

Almost all online services and computer systems store passwords as hashes – but surprisingly, errors still happen. The problems described in the following case study could have been avoided if hashing had been used.

Case study _unit3.1.1 Case study: RockYou

The game and advertising company RockYou suffered a major security breach in 2009 when 32 million user accounts were compromised, revealing that not only did the company store passwords in plaintext, it encouraged insecure passwords by only requiring them to be five alphanumeric characters long.

RockYou’s problems were made worse when it became clear that they had known that their database was vulnerable to an attack for more than ten years. The company had previously been criticised on privacy grounds for sending emails containing complete lists of their advertising partners, and for poor security in issuing passwords through insecure email.

Even when hashing and encrypted communications are used, there are still ways in which attackers can successfully learn your password.

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