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Encryption is the process of converting data into secret, incomprehensible code such that only intended parties are capable of understanding the information. The process of encryption transforms the original data, known as plaintext, into a secret code known as ciphertext. The opposite process, known as decryption, transforms the ciphertext back into plaintext.

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Encryption is used by almost every digital device and service in order to protect data against unauthorized parties or malicious attackers. Strong encryption allows users to safely browse the internet, securely protect their data with passwords, and message one another in privacy.

There are many types of encryption schemes, each with different levels of security. In most cases, one or more keys are used to encrypt and decrypt the data. The type and number of keys required depends on the encryption scheme. Some encryption schemes are thought to be secure against even quantum computers, while others have been proven insecure against regular computers or human calculations.

For example, the Caesar cipher, thought to be used by Julius Caesar, is now known to be easily cracked using letter frequency analysis, while the Enigma used during World War II was cracked by Alan Turing’s invention of modern computers. The Advanced Encryption Standard (AES) is thought to be secure and is currently used by the NSA.

Most modern encryption uses asymmetric encryption. Asymmetric encryption allows a user to encrypt data using a public key, while only the corresponding private key can be used to decrypt the data. This allows two parties to communicate securely and privately over public and insecure channels.

For example, if Alice wishes to send a message to Bob, Bob generates a private key and uses this private key to generate a public key. He sends this public key to Alice, not caring who else sees the public key. Alice can then use the public key to encrypt her message, and send the encrypted message or ciphertext to Bob, again not caring who else sees the ciphertext. Along the way, no third party is capable of reading or altering the original message. Assuming Bob kept his private key secure, only Bob can decipher and read the message.