CISSP考试指南笔记：3.14 加密的方法

Symmetric vs. Asymmetric Algorithms

Cryptography algorithms are either symmetric algorithms, which use symmetric keys (also called secret keys), or asymmetric algorithms, which use asymmetric keys (also called public and private keys).

Symmetric Cryptography

In a cryptosystem that uses symmetric cryptography, the sender and receiver use two instances of the same key for encryption and decryption. So the key has dual functionality, in that it can carry out both encryption and decryption processes. Symmetric keys are also called secret keys, because this type of encryption relies on each user to keep the key a secret and properly protected.

The following list outlines the strengths and weakness of symmetric key systems:

Strengths:

• Much faster (less computationally intensive) than asymmetric systems.
• Hard to break if using a large key size.

Weaknesses:

• Requires a secure mechanism to deliver keys properly.
• Each pair of users needs a unique key, so as the number of individuals increases, so does the number of keys, possibly making key management overwhelming.
• Provides confidentiality but not authenticity or nonrepudiation.