The Key

Abstract

This chapter will introduce the key, which is perhaps one of the most important aspects of any cryptographic system. A system is only as secure as the key. This was noted by Auguste Kerckhoffs in the nineteenth century and has since become known as Kerchoffs’ principle. Random values, secrets, keys, physically unclonable functions (PUFs), and trusted key storage will be covered in this chapter along with functions used to create, update, or freshen keys. Other important characteristics to be discussed include key length, key lifetime, key backup, key destruction, key recovery, and key revocation. An introduction to security equivalence is also provided since this relies heavily on key length. Various methods for storage of keys will be outlined along with a discussion of trusted platform modules (TPMs). In addition, a networks on chip (NoC) view of keys and their storage and use are also provided.

The specific value of keys may also be constrained by the cryptographic application in which they are used. For example, typically there are fewer constraints on symmetric keys as compared with public–private key pairs where special mathematical properties are required. Various techniques for generating keys and tests for randomness will be discussed in this chapter. In cryptographic theory, there are two general types of keys, symmetric keys and public (or asymmetric) keys (see Chaps. 4 and 5). There are different approaches to implementing public key schemes such as those based upon integer factorization (such as RSA), discrete logarithms (DSA, ElGamal), both discussed in Chap. 4 and Elliptical curve discrete logarithms (ECC), discussed in Chap. 5. Key distribution center, or KDC, key translation center, or KTC, and certificate authorities (CA) are third parties or trusted sources and are discussed further in Chap. 4. A more in-depth discussion of other key systems, such as identity key systems, can be found in Menezes et al. (1996). This chapter will discuss key generation and characteristics including key length, an important parameter dictating security, as well as how keys are restricted to be used with different sets of applications.