2 cissp ® Official Study Guide Eighth Edition

Chapter 
7

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In Chapter 6, “Cryptography and Symmetric Key Algorithms,” 
we introduced basic cryptography concepts and explored a 
variety of private key cryptosystems. These symmetric cryp-
tosystems offer fast, secure communication but introduce the substantial challenge of key 
exchange between previously unrelated parties.
This chapter explores the world of asymmetric (or public key) cryptography and the 
public-key infrastructure (PKI) that supports worldwide secure communication between 
parties that don’t necessarily know each other prior to the communication. Asymmetric 
algorithms provide convenient key exchange mechanisms and are scalable to very large 
numbers of users, both challenges for users of symmetric cryptosystems.
This chapter also explores several practical applications of asymmetric cryptography: 
securing email, web communications, electronic commerce, digital rights management, and 
networking. The chapter concludes with an examination of a variety of attacks malicious 
individuals might use to compromise weak cryptosystems.
Asymmetric Cryptography
The section “Modern Cryptography” in Chapter 6 introduced the basic principles behind 
both private (symmetric) and public (asymmetric) key cryptography. You learned that sym-
metric key cryptosystems require both communicating parties to have the same shared 
secret key, creating the problem of secure key distribution. You also learned that asym-
metric cryptosystems avoid this hurdle by using pairs of public and private keys to facilitate 
secure communication without the overhead of complex key distribution systems. The secu-
rity of these systems relies on the difficulty of reversing a one-way function.
In the following sections, we’ll explore the concepts of public key cryptography in 
greater detail and look at three of the more common public key cryptosystems in use today: 
Rivest–Shamir–Adleman (RSA), El Gamal, and the elliptic curve cryptography (ECC).