Ecc Fp Modular Add; Modular Add Register Usage - Motorola DigitalDNA MPC180E User Manual

7.3.4 ECC F Modular Add
p
Modular addition may be performed on any two vectors loaded into A (A0-A3) and B
(B0-B3), where both of these vectors are less than the value stored in the modulus register
N (N0-N3). The results are stored in the respective B register. For ECC functionality, this
function is used by the point add and point double routines but is available to the host
interface - typically for higher-level ECC-related functions. This function operates with a
minimum of four digits (Modsize = 3).
Prior to initiating this function, the A, B and N register pointers must be set in the control
register which indicate which sub-registers (e.g A0, B0, A1, B1, etc.) are the targeted
operands. See Table 7-2 for a detailed description. Once this is performed, the host
processor may successfully initiate this function.
Computation C = D + E mod N, where D, E, and C are integers and are less than N
Entry name modularadd
Entry address 0x008(modularadd)
Pre-conditions A0-3 = D (integer, exact A-location pre-selected in Control Register)
B0-3 = E (integer, exact B-location pre-selected in Control Register)
N0-3 = prime p (modulus) of the ECC system
Post-conditions B0-3 = results of modular addition stored where the B operand was located
Unless explicitly noted, all other registers are not guaranteed to be any particular value.
Special The function operates the same regardless of whether or not the operands are in the Montgomery
conditions residue system.
Initial Condition
modulus N (if N0 selected)
PRELIMINARY—SUBJECT TO CHANGE WITHOUT NOTICE
Table 7-8. Modular Add
B3
B2
B1
B0
E (if B0 selected)
A3
A2
A1
D (if A0 selected)
A0
N3
N2
N1
N0
'1' - ECC enabled ECC
EXP(k)
XYZ
'0' - F enabled F2M
p
regAsel
set (00, 01, 10, 11)
regBsel
set (00, 01, 10, 11)
regNsel
set (00, 01, 10, 11)
Modsize
set
EXP(k)_SIZE
Figure 7-7. Modular Add Register Usage
Chapter 7. Public Key Execution Unit
Modular Add
Final Condition
?
?
?
C (if B0 selected)
?
?
?
modulus N (if N0 selected)
same
same
same
same
same
same
ECC Routines
7-13