5812-DS00-R datasheet(34/84 Pages) BOARDCOM

34 / 84 page

BCM5812

Advance Data Sheet

3/11/03

B roa dcom Co rpo rat ion

Page 26

Cryptographic Operations

Document

5812-DS01-405-R

Figure 24: Counter Mode

In counter mode, the BCM5812 takes the initial count value from the IV field. Each subsequent block is incremented by one

in the least significant bit position.

DIFFIE-HELLMAN

The Diffie-Hellman public key algorithm is used for key agreement in a number of protocols, including IKE, SSL, and TLS. It

is based on the difficulty of calculating discrete logarithms in a finite field, and typically involves the following steps [17]:

Alice and Bob agree on parameters for a group, defined in terms of a large prime base, N, and a generator, g. The

generator is such that each x less than N generates a different value (y = gx mod N).

Alice chooses a secret random number, xa and sends Bob, yA = g

xa mod N over a public channel.

Bob does the same thing, choosing his secret number xb, and sends Alice yB = g

xb mod N.

Alice exponentiates Bob’s public number and computes (yb

xa mod N), which equals (gxa)xbmod N

Bob similarly computes (ya

xb mod N), which equals (gxb)xamod N, the shared secret.

The BCM5812 provides separate Diffie-Hellman operation codes for generating the public key and for generating the secret

key. Figure 25 on page 28 shows the command context, packet descriptor structure, input, and output data for Diffie-

Hellman public key generate. This command uses opcode 0x01, and MCR2@.

5812-DS00-R Datenblatt(PDF) 34 Page - Broadcom Corporation.