Cryptography (also known as cryptology; comes from Greek κρυπτός, kryptos, "hidden, secret"; and γράφω, gráphō, "I write", or -λογία, -logia, respectively) is the practice and study of hiding information. It is sometimes called code breaking, but this is not really a correct name. It is the science used to try to keep information secret and safe. Modern cryptography is a mix of mathematics, computer science, and electrical engineering. Cryptography is used in ATM (bank) cards, computer passwords, and shopping on the internet.
Using Cryptography [change]
When a message is sent using cryptography, it is changed (or encrypted) before it is sent. The change makes the message hard to read. If someone wants to read it, they need to change it back (or decrypt it). How to change it back is a secret. Both the person that sends the message and the one that gets it should know the secret way to change it, but other people should not be able to.
Types of Cryptography [change]
Different types of cryptography can be easier or harder to use and can hide the secret better or worse.
In symmetric cryptography, both the sender and receiver share a secret which is often called a key. The sender uses the key in a certain way to hide the message. Then, the receiver will use the same key in the opposite way to reveal the message. Most types of cryptography are symmetric.
Asymmetric cryptography is harder to use. Each person who wants to use asymmetric cryptography uses a secret number, and a different number that they can tell everyone. If someone else wants to send this person a message, they'll use the number they've been told to hide the message. Now the message cannot be revealed, even by the sender, but the receiver can easily reveal the message with his secret number. This way, nobody else needs to know the secret.
The details of asymmetric cryptography make it less useful than symmetric cryptography for actually sending messages. Instead, it is often used for computer signatures, when a computer must know that a file was sent from a certain sender. For example, computer software companies that release updates for their software may want to sign those updates to prove that the update was made by them, so that hackers cannot make their own updates that would cause harm.
Computers can do hard math very fast, and because of this they can do very strong encryption. Examples are computer algorithms like RSA, AES, Blowfish, and many others. Using good algorithms like these can make it very hard to read the information that is sent.
People are better at patterns, changing order of words or letters, and using words with different meanings. Because people are slower than computers, any cryptography they use can probably be broken if enough of the secret way to change it is known.
- Liddell and Scott's Greek-English Lexicon. Oxford University Press. (1984)
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