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MPC185 Security Processor Technical Summary

MOTOROLA

cryptographic function. For example, at the highest level, the accelerator performs modular exponentiations

to support RSA and performs point multiplies to support ECC. At the lower levels, the PKEU can perform

simple operations such as modular multiplies.

7.1.1 Elliptic Curve Operations

The PKEU has its own data and control units, including a general-purpose register file in the

programmable-size arithmetic unit. The field or modulus size can be programmed to any value between 160

bits and 512 bits in programmable increments of 8, with each programmable value i supporting all actual

field sizes from i*8 -7 to i*8. The result is hardware supporting a wide range of cryptographic security.

Larger field / modulus sizes result in greater security but lower performance; processing time is determined

by field or modulus size. For example, a field size of 160 is roughly equivalent to the security provided by

1024 bit RSA. A field size set to 208 roughly equates to 2048 bits of RSA security.

The PKEU contains routines implementing the atomic functions for elliptic curve processing—point

arithmetic and finite field arithmetic. The point operations (multiplication, addition and doubling) involve

one or more finite field operations which are addition, multiplication, inverse, and squaring. Point add and

double each use of all four finite field operations. Similarly, point multiplication uses all EC point operations

as well as the finite field operations. All these functions are supported both in modular arithmetic as well as

polynomial basis finite fields.

7.1.2 Modular Exponentiation Operations

The PKEU is also capable of performing ordinary integer modulo arithmetic. This arithmetic is an integral

part of the RSA public key algorithm; however, it can also play a role in the generation of ECC digital

signatures and Diffie-Hellman key exchanges.

Modular arithmetic functions supported by the MPC185’s PKEU include the following:

R 2 mod N

A’ E mod N

(A

(A

(A + B) mod N

(A – B) mod N

Where the following variable definitions: A’ = AR mod N, N is the modulus vector, A and B are input

multiple of 32.

The PKEU can perform modular arithmetic on operands up to 2048 bits in length. The modulus must be

larger than or equal to 129 bits. The PKEU uses the Montgomery modular multiplication algorithm to

perform core functions. The addition and subtraction functions exist to help support known methods of the

Chinese Remainder Theorem (CRT) for efficient exponentiation.

7.2 Data Encryption Standard Execution Unit (DEU)

The DES Execution Unit (DEU) performs bulk data encryption/decryption, in compliance with the Data

Encryption Standard algorithm (ANSI x3.92). The DEU can also compute 3DES and extension of the DES

Freescale Semiconductor, Inc.

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