Hash functions are important in data security. SHA-256 (Secure Hash Algorithm) converts text of any length to a 64-digit hexadecimal number. Play around with the hash generator here by copying and pasting text into it.
Here's a Shakespeare quote:
Life's but a walking shadow, a poor player, that struts and frets his hour upon the stage, and then is heard no more; it is a tale told by an idiot, full of sound and fury, signifying nothing.
The SHA-256 hash is:
CCF93A73CA8089926E3511F7FEDACB4450415E6726677BA071B9995FAF569F00
If you change a single character, the hash is completely different. If you take the end period off the quote, the hash becomes:
DD1912DD6274B91DCD3302D7C6C37FB52DCF7E0C516F39E6AD64ECB9FCBE9417
Hashes are "one-way" — it's easy to generate a hash from any text, but there is no know way to convert a hash back into the source text. In other words, if you are given this hash:
9A9680545E3BDDB29751764C55AA8519FC2FF55C9D7588C440C6E12261193FEC
The only way to get the source text is by guessing. How long would it take? The video above shows you that it would take a long time, indeed.
If this kind of thing interests you, I highly recommend Simon Singh's The Code Book, which clearly explains cryptographic principles.
