RSA Security 5.2.2 manual Parameter Generation, Phase

Cryptography Overview

•Phase 1

•Phase 2

Phase 1

Alice

Private value

Public value

Phase 2

Alice

Agreed upon

key

Parameters

Bob

Private value

Public value

Bob

=Agreed upon

key

Figure 3-12The Diffie-Hellman Key Agreement Protocol

Parameter Generation

A central authority selects a prime number p of length k bytes, and an integer g greater than 0 but less than p, called the base. The central authority may optionally select an integer l, the private-value length in bits, that satisfies 2l–1≤ p.

Phase 1

Each of the two parties executing the Diffie-Hellman protocol does the following:

1.Each party, i, i = 1 or 2, randomly generates a private value, which is a number, xi,

greater than 0 but less than the prime. If the central authority has specified the length l, the private value shall satisfy 2l–1≤ xi < 2l.

2.Each party computes a public value yi = gxi mod p.

C h a p t e r 3 C r y p t o g r a p h y 6 3