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* Cryptography is the science and art of transforming messages to make them secure and immune to attack.
* Encryption renders a message (plaintext) unintelligible to unauthorized personnel.
* Decryption transforms an intentionally unintelligible message (ciphertext) into meaningful information.
* Cryptography algorithms are classified as either symmetric-key methods or public-key methods.
* In symmetric-key cryptography the same secret key is used by the sender and the receiver.
* Substitution ciphers are either monoalphabetic or polyalphabetic.
* The P-box, S-box, and product block are methods used by block ciphers.
* DES is a symmetric-key method adopted by the U.S. government, but it has been replaced by Triple DES or other methods.
* Operation modes to handle long messages include ECB mode, CBC mode, CFM, and CSM.
* In public-key cryptography, the public key is used by the sender to encrypt the message; the private key is used by the receiver to decrypt the message.
* One of the commonly used public-key cryptography methods is the RSA algorith.