5812-DS00-R datasheet(37/84 Pages) BOARDCOM

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Advance Data Sheet

BCM5812

3/11/03

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5812-DS01-405-R

Cryptographic Operations

Page 29

Figure 26: Diffie-Hellman Secret Key

The modulus must be input in the command context as a BigNum in the same manner as for Diffie-Hellman generate. The

first Input fragment chain entry buffer address specifies the input secret, and the second input fragment chain entry buffer

contains the peer entity’s public value. The shared secret is output to the output fragment address in the packet descriptor

structure. All of these are BigNum values.

All output buffers must be sized for the appropriate parameter argument parameter field size in Table 10.

The lengths of the Diffie-Hellman generate and shared secret command contexts depend upon the parameter field sizes,

and range from 82 to 524 bytes.

RSA

The RSA public key algorithm is used for digital signature authentication and key exchange in IKE, SSL, and TLS. It also

widely used in a number of other applications, such as Public Key Infrastructure (PKI) products. RSA is a two-key system,

with a public key that can be used to either encrypt a value so that only the holder of the private key can decrypt it, or to

decrypt a value that only the holder of the private key could have encrypted [17][19].

RSA uses the product of two large primes, p and q, which must remain secret. The public key consists of n = p * q, and a

public exponent e that is relatively prime to (p-1)*(q-1). The public key operation encrypts a message m by exponentiating

it modulo n, so that the encrypted value x = me mod n. The private key consists of the modulus and a decrypting exponent,

d, that is the inverse of e, d = e-1 mod (p-1)(q-1). Knowing p and q, it is straight forward to compute d, but otherwise quite

difficult. Decryption is simply m = xd mod n.

LENGTH

OPCODE

MODULUS

64-256

Bytes

MODULUS LENGTH

EXPONENT LENGTH

COMMAND CONTEXT ADDRESS

NEXT INPUT FRAGMENT CHAIN ENTRY

RESERVED

INPUT FRAGMENT LENGTH

INPUT FRAGMENT ADDRESS

RESERVED

NEXT OUTPUT FRAGMENT CHAIN ENTRY

RESERVED

OUTPUT BUFFER LENGTH

OUTPUT FRAGMENT ADDRESS

NEXT INPUT FRAGMENT CHAIN ENTRY

RESERVED

FRAGMENT LENGTH

INPUT FRAGMENT ADDRESS

Input Public Value

Input Secret

Output Shared Secret

Packet Descriptor

Command Context

LENGTH

OPCODE

MODULUS

64-256

Bytes

MODULUS LENGTH

EXPONENT LENGTH

COMMAND CONTEXT ADDRESS

NEXT INPUT FRAGMENT CHAIN ENTRY

RESERVED

INPUT FRAGMENT LENGTH

INPUT FRAGMENT ADDRESS

RESERVED

NEXT OUTPUT FRAGMENT CHAIN ENTRY

RESERVED

OUTPUT BUFFER LENGTH

OUTPUT FRAGMENT ADDRESS

NEXT INPUT FRAGMENT CHAIN ENTRY

RESERVED

FRAGMENT LENGTH

INPUT FRAGMENT ADDRESS

NEXT INPUT FRAGMENT CHAIN ENTRY

RESERVED

FRAGMENT LENGTH

INPUT FRAGMENT ADDRESS

Input Public Value

Input Secret

Output Shared Secret

Packet Descriptor

Command Context

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