| Lesson 4 | Encryption and decryption |
| Objective | Define encryption and decryption. |
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
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 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
