It all begins with mathematics really - the one true scientific language, so they say. Cryptography has been around as early as 4000 years ago, doing what it still does today - ensuring that secrets stay secret.
The early Egyptians used it to keep their esoteric religious knowledge to themselves. The ancient Chinese employed it to keep their secrets to the higher social class. Julius Caesar depended on it to ensure that his own couriers would not read his messages.
It comes from the Greek word Kryptos, meaning 'hidden', and that's its purpose - to hide information so that it cannot be compromised.
Today it's a core technology of the Information Age, the mathematical science (and some would say art) of scrabbling information in such a way as to be undecipherable to all except those whom it is intended for.
It is the building block of secure data transmission between parties in a potentially hostile environment, and though it is not enough by itself, do not underestimate its necessity.
Through cryptography, information (whether text or numerical data) undergoes a transformation that makes it appear like gibberish. Anyone who intercepts it would see a bunch of numbers that don't make any kind of sense at all. The only way for someone to make sense of it would be to know what kind of transformation was applied in order to change the gibberish back to understandable information again.
Read more about PKI in Asia.