Encryption And Decryption; Symmetric-Key Encryption - Red Hat CERTIFICATE SYSTEM 7.3 - ADMINISTRATION Administration Manual

Appendix B. Introduction to Public-Key Cryptography
• Encryption and decryption allow two communicating parties to disguise information they send to
each other. The sender encrypts, or scrambles, information before sending it. The receiver decrypts,
or unscrambles, the information after receiving it. While in transit, the encrypted information is
unintelligible to an intruder.
• Tamper detection allows the recipient of information to verify that it has not been modified in transit.
Any attempts to modify or substitute data are detected.
• Authentication allows the recipient of information to determine its origin by confirming the sender's
identity.
• Nonrepudiation prevents the sender of information from claiming at a later date that the information
was never sent.
B.2. Encryption and Decryption
Encryption is the process of transforming information so it is unintelligible to anyone but the intended
recipient. Decryption is the process of decoding encrypted information. A cryptographic algorithm,
also called a cipher, is a mathematical function used for encryption or decryption. Usually, two related
functions are used, one for encryption and the other for decryption.
With most modern cryptography, the ability to keep encrypted information secret is based not on
the cryptographic algorithm, which is widely known, but on a number called a key that must be used
with the algorithm to produce an encrypted result or to decrypt previously encrypted information.
Decryption with the correct key is simple. Decryption without the correct key is very difficult, if not
impossible.
The following sections cover using keys for encryption and decryption:
Section B.2.1, "Symmetric-Key Encryption"
•
Section B.2.2, "Public-Key Encryption"
•
Section B.2.3, "Key Length and Encryption Strength"
•
B.2.1. Symmetric-Key Encryption
With symmetric-key encryption, the encryption key can be calculated from the decryption key and vice
versa. With most symmetric algorithms, the same key is used for both encryption and decryption, as
Figure B.1, "Symmetric-Key
shown in
Figure B.1. Symmetric-Key Encryption
Implementations of symmetric-key encryption can be highly efficient, so that users do not experience
any significant time delay as a result of the encryption and decryption. Symmetric-key encryption also
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Encryption".