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Calculate the parameters from E:
EP = E
–1
mod(P – 1) EQ = E
–1
mod(Q – 1) Rval = P
–1
mod(Q)
In this computation, the following parameters need to be provided:
X the input number (pointed by {nu1XBase,2*u2ModLength +16})
P and Q the primes (pointed by {nu1ModBase,2*u2ModLength +8}).
EP and EQ the reduced exponents (pointed by {pfu1ExpBase,2*u2ExpLength +8})
Rval and Precomp (pointed by{nu1PrecompBase,RAndPrecompLen})
Blinding the exponent blinding value (provided inu1Blinding)
The length RAndPrecompLen depends on the lengths and options chosen; its calculus is detailed in
Options below.
The service for this operation is CRT.
Note:  The minimum value for u2ModLength is 12 bytes. Therefore, the significant length of P or Q must
be at least three 32-bit words.
43.3.5.4.4 Parameters Definition
The following table shows the parameter block for the CRT service.
Many parameters have complex placement in memory; therefore, detailed figures are provided in CRT
Service Placement below.
Table 43-62. CRT Service Parameters
Parameter Type Direction Location Data Length Before
Executing the
Service
After
Executing
the Service
u2Options u2 I Options (see
below)
Options (see
below)
nu1ModBase nu1 I Crypto
RAM
2*u2ModLength
+ 8
Base of P, Q Base of P, Q
untouched
u2ModLength u2 I Length of P or Q
greater than or
equal to 12
Length of P or
Q
nu1XBase (see
Note 1)
nu1 I Crypto
RAM
2*u2ModLength
+ 16
Base of X Base of X
Filled with the
result
nu1PrecompBase nu1 I Crypto
RAM
See Options
below
Base of Rvalue
and Pre
computations
workspace
Corrupted
pfu1ExpBase (see
Note 2)
pfu1 I Any place 2*u2ExpLength
+ 8
Base of EP, EQ Base of EP,
EQ untouched
u2ExpLength u2 I Significant length
of EP or EQ
Significant
length of EP
or EQ
SAM D5x/E5x Family Data Sheet
Public Key Cryptography Controller (PUKCC)
© 2019 Microchip Technology Inc.
Datasheet
DS60001507E-page 1502