ABSTRACT
In this chapter, the authors study several signature schemes, but first they discuss some fundamental differences between conventional and digital signatures. They cover various signature schemes based on the Factoring and Discrete Logarithm problems, including the Digital Signature Standard. The authors introduce the notion of security for signature schemes and how hash functions are used in conjunction with signature schemes. Hence, they do not seem to represent a threat to the security of the ElGamal Signature Scheme, provided that a secure hash function is used as described in the chapter. However, the Schnorr Signature Scheme integrates a hash function directly into the signing algorithm. Many people suggested that the modulus size not be fixed, so that larger modulus sizes could be used if desired. Certificates can be distributed or redistributed to anyone, and possession of a certificate does not imply ownership of it.
