ST STM32WL5 Series, Reference Manual, Page: 711 / 1454

RM0453 Rev 2 711/1454
RM0453 Public key accelerator (PKA)
721
When performing this operation following special cases should be noted:
•
For k = 0, this function returns a point at infinity, that is (0, 0) if curve parameter b is
nonzero and (0, 1) otherwise. For k different from 0 it might happen that a point at
infinity is returned. When the application detects this behavior a new computation
should be carried out.
•
For k < 0 (i.e. a negative scalar multiplication is required) multiplier absolute value
k = |-k| should be provided to the PKA. After the computation completion, the formula
-P = (x, -y) can be used to compute the y coordinate of the effective final result (the x
coordinate remains the same).
24.4.16 ECDSA sign
ECDSA signing operation (outlined in Section 24.3.5 ) is summarized in Table 162 (input
parameters) and in Table 163 (output parameters).
The application should check if the output error is equal to zero, if it is different from zero a
new k should be generated and the ECDSA sign operation should be repeated.
Table 161. ECC Fp scalar multiplication (Fast Mode)
Parameters with direction Value (Note) Storage Size
IN MODE 0x22 PKA_CR 6 bits
IN
Scalar multiplier k length
(In bits, not null,
8 < value < 640)
RAM@0x400
32 bits Modulus length
(In bits, not null,
8 < value < 640)
RAM@0x404
Curve coefficient a sign
0x0: positive
0x1: negative
RAM@0x408
IN
Curve coefficient |a| (Absolute value, |a| < p) RAM@0x40C
EOS
Curve modulus value p
(Odd integer prime,
0 < p < 2
640
)
RAM@0x460
Scalar multiplier k (0 ≤ k < 2
640
) RAM@0x508
Point P coordinate x
P
(x < p ) RAM@0x55C
Point P coordinate y
P
(y < p ) RAM@0x5B0
IN
Montgomery parameter
R
2
mod p
(mandatory) RAM@0x4B4
OUT
Result: k x P coordinate x (result < p ) RAM@0x55C
Result: k x P coordinate y (result < p ) RAM@0x5B0