Up until very recently people's wealth, mostly coins and jewels, was kept safe under lock and key. Rich medieval families would keep a strong box with a large key, both of which were carefully hidden in different places. Later the box may have been kept in a bank. In either case, potential thieves would need to find both the box and the key. A similar principle was used for sending secret diplomatic and military messages. The messages were written in code with both the sender and the receiver having the key to the code. Thus, while the message could be discovered its meaning could only be found if the 'key' was also known. And so began a long-running battle between code-makers who tried to make better keys, and code-breakers who sought ways of finding them. Nowadays, cryptography is central to how our money is kept secure, even though we may not be aware of it. Our money is no longer in a tangible form, but in the form of information kept with our banks. To keep everyone involved happy, the messages initiated by our plastic cards have to be sent and received safely and the entire operation must be carried out with a high level of confidentiality and security.