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## Encryption and decryption (Definition)

In *cryptography*, a message that humans can read is called *plaintext*, or cleartext. As shown in the image below,
the process of scrambling a message to make it unreadable by humans is called *encryption*, and the resulting message is called *ciphertext*.

The reverse process, called decryption, takes an encrypted (or ciphertext) message and restores it to the original plaintext - decryption unscrambles the message.

### Ciphers and keys

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Lesson 4 | Encryption and decryption |

Objective | Define encryption and decryption. |

The reverse process, called decryption, takes an encrypted (or ciphertext) message and restores it to the original plaintext - decryption unscrambles the message.

A cryptographic *algorithm* is a procedure that uses a *cipher* to encrypt and decrypt plaintext messages. A cipher is a mathematical function.
The *keys* are the numbers or values that are used in this mathematical function, or cipher.

The key is simply a binary number, represented in hexadecimal. Keys usually use only the characters: 0-9 and A-F.
The characters that make up the key are usually grouped in pairs, or fours. To the human eye, a key might look something like this:

All modern encryption algorithms use a key to decrypt a ciphertext message.

As you can imagine, most attacks on cryptographic systems, called*cryptanalysis, focus on finding that encryption key. *

In the next lesson, you will identify various methods of attacking encrypted data.

Click the link below to review the implementation of encryption by matching terms with their definitions.**Encryption Types Methods**

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All modern encryption algorithms use a key to decrypt a ciphertext message.

As you can imagine, most attacks on cryptographic systems, called

In the next lesson, you will identify various methods of attacking encrypted data.

Click the link below to review the implementation of encryption by matching terms with their definitions.