Symmetric-Key Encryption; Public-Key Encryption - Red Hat CERTIFICATE SYSTEM 8 - DEPLOYMENT Deployment Manual

Chapter 1. Introduction to Public-Key Cryptography
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.

1.1.1. 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 1.1, "Symmetric-Key Encryption".
shown in
Figure 1.1. 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
provides a degree of authentication, since information encrypted with one symmetric key cannot be
decrypted with any other symmetric key. Thus, as long as the symmetric key is kept secret by the two
parties using it to encrypt communications, each party can be sure that it is communicating with the
other as long as the decrypted messages continue to make sense.
Symmetric-key encryption is effective only if the symmetric key is kept secret by the two parties
involved. If anyone else discovers the key, it affects both confidentiality and authentication. A person
with an unauthorized symmetric key not only can decrypt messages sent with that key, but can encrypt
new messages and send them as if they came from one of the legitimate parties using the key.
Symmetric-key encryption plays an important role in SSL communication, which is widely used for
authentication, tamper detection, and encryption over TCP/IP networks. SSL also uses techniques of
public-key encryption, which is described in the next section.

1.1.2. Public-Key Encryption

Public-key encryption (also called asymmetric encryption) involves a pair of keys, a public key and
a private key, associated with an entity. Each public key is published, and the corresponding private
Section 1.3,
key is kept secret. (For more information about the way public keys are published, see
"Certificates and Authentication".) Data encrypted with a public key can be decrypted only with the
Figure 1.2, "Public-Key Encryption"
corresponding private key. shows a simplified view of the way
public-key encryption works.
Figure 1.2. Public-Key Encryption
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