MOTOROLA

MPC180 Security Processor Technical Summary

5

Public Key Execution Unit (PKEU)

producing n sets of encrypted (ciphertext) blocks. Decryption is handled in the reverse manner. The

ciphertext blocks are processed one at a time by a DES module in the recipient’s system. The same key is

used, and the DEU manages the key processing internally so that the plaintext blocks are recovered.

The DES/3DES execution unit supports the following modes:

•

ECB (electronic code book)

•

CBC (cipher block chaining)

In addition to these modes, the DEU can compute Triple-DES. Triple-DES is an extension to the DES

algorithm in which every 64-bit input block is processed three times. There are several ways that Triple-DES

can be computed. The DES accelerator on the MPC180 supports two key (K1, K2, K1) or three key (K1,

K2, K3) Triple-DES.

THe MPC180 supports two of the modes of operation defined for Triple-DES (see draft ANSI Standard

X9.52-1998):

•

TECB (Triple DES analogue of ECB)

•

TCBC (Triple DES analogue of CBC)

6.3 ARC Four Execution Unit (AFEU)

The AFEU processes an algorithm that is compatible with the RC4 stream cipher from RSA Security, Inc.

The RC4 algorithm is byte-oriented; therefore, a byte of plaintext is encrypted with a key to produce a byte

of ciphertext. The key is variable length, and the AFEU supports 40-bit to 128-bit key lengths, providing a

wide range of security levels. RC4 is a symmetric algorithm, so each of the two communicating parties share

the same key.

AFEU processing begins after this shared session key is agreed upon. The plaintext message to be encrypted

is logically partitioned into n sets of 8-bit blocks. In practice, the host processor groups 4 bytes at a time into

32-bit blocks and write that data to the AFEU. The AFEU internally processes each word one byte at a time.

The AFEU engine processes each block in turn, byte by byte, producing n sets of encrypted (ciphertext)

blocks. Decryption is handled in the reverse manner. The ciphertext blocks are processed one at a time by

an AFEU in the recipient’s system. The same key is used, and the AFEU manages the key processing

internally so that the plaintext blocks are recovered.

The AFEU accepts data in 32-bit words per write cycle and produces 4 bytes of ciphertext for every 4 bytes

of plaintext. Before any processing occurs, the key data is written to the AFEU, after which an initial

permutation on the key happens internally. After the initial permutation is finished, processing on 32-bit

words can begin.

6.4 Message Authentication Unit (MAU)

The MAU can perform SHA-1, MD5 and MD4, three of the most popular public message digest algorithms.

At its simplest, the MAU receives 16 32-bit registers containing a message, and produces a hashed message

of 128 bits for MD4/MD5 and 160 bits for SHA-1. The MAU also includes circuitry to automate the process

of generating an HMAC (hashed message authentication code) as specified by RFC 2104. The HMAC can

be built upon any of the hash functions supported by MAU.