5812-DS01-R datasheet(27/84 Pages) BOARDCOM

27 / 84 page

Advance Data Sheet

BCM5812

3/11/03

B roa dcom Co rpo rat ion

Document

5812-DS01-405-R

Cryptographic Operations

Page 19

Figure 18: SSL/TLS DES/3DES Command Context

The same packet descriptor and fragment processing formats are used as for IPsec as well.

ARCFOUR

The BCM5812 provides ARCFOUR, a stream cipher that is compatible with the RSA Security RC4ΤΜ algorithm.

ARCFOUR is described in Applied Cryptography, Second Edition [17], in terms of pseudo-code using a 256 byte ARCFOUR

state array and two variables, i and j.

Initialize the ARCFOUR state array S such that S[n]=n. Set variables i and j to 0,

Initialize another 256 byte array such that K[n] contains the n-th byte of the key. If the key contains fewer than 256 bytes,

continue by putting the first key byte in the next K entry, and so forth, until K is filled.

Perform the following once, to set up the ARCFOUR state using the key, where swap exchanges the byte values for the

specified pair of elements:

for (i=0; i<256; i++){

j = (j+S[i]+K[i]) & 0xff;

swap(S[i],S[j]);

}

Use the ARCFOUR state array to generate the next keystream byte, O:

i = (i+1) & 0xff;

j = (j+S[i]) & 0xff;

swap(S[i],S[j]);

O = S[(S[i]+S[j]) & 0xff];

Exclusive-or O with input data to encipher the next byte in the cleartext stream, or to decipher the next byte in the

ciphertext stream.

Figure 19 shows the Command Context used by the BCM5812 for ARCFOUR. The BCM5812 provides sub-operations for

combining the initial ARCFOUR state key step along with encipherment, or just encipherment using a continued ARCFOUR

state. Options control whether the BCM5812 writes back the ARCFOUR state or generates keystream only, without input

data. These options are described in Table 6 on page 20. The command context length is always 268 bytes.

This command uses MCR1@. The Opcode for this command is 0x04.

LENG TH

OP CO DE

DES KEY 1

RESERVED

FLAGS

DES KEY 2

DES KEY 3

8 B ytes

15 1 4 13

Reserved

fla gs

BYTE 3

BYTE 4

BYTE 1

BYTE 2

BYTE 7

BYTE 8

BYTE 5

BYTE 6

DES Key Bit and Byte O rder

132

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