ST STM32L4+ Series Reference Manual page 1175

RM0432 Public key accelerator (PKA) applied to STM32L4P5xx and STM32L4Q5xx only
36.4.3 Modular addition
Modular addition operation consists in the computation of A + B mod n. Operation
instructions are summarized in
Parameters with direction
IN
OUT
36.4.4 Modular subtraction
Modular subtraction operation consists in the following computations:
•
If A ≥ B result equals A - B mod n
•
If A < B result equals A + n - B mod n
Operation instructions are summarized in
Parameters with direction
IN
OUT
36.4.5 Modular and Montgomery multiplication
In order to be more efficient when performing a sequence of multiplications the PKA
accelerates multiplication which has input and outputs in the Montgomery domain. The two
main uses of this operation are:
•
Map a value from natural domain to Montgomery domain and vice-versa
•
Perform a modular multiplication A x B mod n
The method to perform above operations are described below. Note that "x" function is this
operation, and A, B, C operands are in the natural domain.
Table
Table 244. Modular addition
MODE 0x0E
Operand length (In bits, not null)
Operand A (0 ≤ A < n)
Operand B (0 ≤ B < n)
Modulus value n (n < 2
Result: A+B mod n (0 ≤ result < n)
Table 245. Modular subtraction
MODE 0x0F
Operand length (In bits, not null)
Operand A (0 ≤ A < n)
Operand B (0 ≤ B < n)
Modulus value n (n < 2
Result: A-B mod n (0 ≤ result < n)
244.
Value (Note)
3136
)
Table 245.
Value (Note)
3136
)
RM0432 Rev 6
Storage
PKA_CR 6 bits
RAM@0x404 32 bits
RAM@0x8B4
RAM@0xA44
RAM@0xD5C
RAM@0xBD0
Storage
PKA_CR 6 bits
RAM@0x404 32 bits
RAM@0x8B4
RAM@0xA44
RAM@0xD5C
RAM@0xBD0
1175/2301
Size
ROS
Size
ROS
1196