Chapter 7. Public Key Execution Unit
7-27
PRELIMINARY—SUBJECT TO CHANGE WITHOUT NOTICE
RSA Routines
7.4.2 RSA Montgomery Modular Multiplication
(
(A
×
B
×
R
-1
) mod N
)
The (A
×
B
×
R
-1
) mod N calculation is the core function of the PKEU. It is used to assist
the exponentiation routine in completing its operation though it is also available to the host
processor - typically to put messages into the Montgomery format. This function operates
with a minimum of five digits (Modsize = 4). The complete set of I/O conditions is shown
below:
Figure 7-18. Modular Multiplication Register Usage
Prior to initiating this function, the A and B 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.
Table 7-19. Modular Multiplication
Modular Multiply
Computation
C = A * B * R
-1
mod N, where A, B, and C are integers less than N and R = 2
16D
where D is the
number of digits of the modulus vector
Entry name
modularmultiply
Entry address
0x00a(modularmultiply)
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
Typically, though it is not mandatory, the operands will be in the Montgomery residue system. The only
time this would not be the case is when manually placing a value into the Montgomery residue system.
N1
N2
N3
A0
A1
A2
A3
B0
B1
B2
B3
Initial Condition
Final Condition
N0
C(
⇑
)
B(
⇑
)
modulus N(
⇑
)
modulus N(
⇑
)
A(
⇑
)
XYZ
F2M
EXP(k)
regAsel
regBsel
regNsel
‘0’ - integer-modulo-n enabled
same
set (00)
set (00)
set (00)
same
same
same
Modsize
EXP(k)_SIZE
set
same
A(
⇑
)
ECC
same
‘0’ - ECC disabled
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Freescale Semiconductor, Inc.
For More Information On This Product,
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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.
..