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RSA Routines
7.4.3 RSA Montgomery Modular Multiplication
((A × B × R
-2
The (A × B × R
) mod N calculation is similar to the standard 'R
multiplication except an additional R is divided out. This function is particularly helpful
when using the Chinese Remainder Theorem. This function operates with a minimum of
five digits (Modsize = 4). The complete set of I/O conditions is shown below:
Table 7-20. Modular Multiplication (with double reduction)
Computation
C = A * B * R
number of digits of the modulus vector
Entry name
modularmultiply2
Entry address
0x00b(modularmultiply2)
Pre-conditions
A0-3 = A
B0-3 = B
N0-3 = modulus
Post-conditions
A0-3 = A operand is preserved
B0-3 = results of modular multiplication stored where the B operand was located
Unless explicitly noted, all other registers are not guaranteed to be any particular value.
Special
—
conditions
Initial Condition
Figure 7-19. Modular Multiplication (with double reduction) Register Usage
7-28
PRELIMINARY—SUBJECT TO CHANGE WITHOUT NOTICE
-2
) mod N)
Modular Multiply (with double reduction)
-2
mod N, where A, B, and C are integers less than N and R
B3
B2
B1
B0
B(⇑)
A3
A2
A1
A(⇑)
A0
N3
N2
N1
N0
modulus N(⇑)
ECC
'0' - ECC disabled
EXP(k)
XYZ
F2M
'0' - integer-modulo-n enabled
regAsel
set (00)
regBsel
set (00)
regNsel
set (00)
Modsize
set
EXP(k)_SIZE
MPC180E Security Processor User's Manual
-1
16D
= 2
Final Condition
C(⇑)
A(⇑)
modulus N(⇑)
same
same
same
same
same
same
' Montgomery
where D is the
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