Datasheet

• CarryOperand (provided through the Carry Options and Carry values)
Important: Even if neither accumulation nor subtraction is specified, the nu1ZBase must
always be filled and point to a Crypto RAM space. It this case, nu1ZBase can point to the same
space as the nu1RBase.
If using the big modular reduction option, the Multiply operation is followed by a reduction (see 43.3.5.1
Modular Reduction). In this case, the length of Cns is 64 bytes.
If using the modular reduction option, the Multiply operation is followed by a reduction (see 43.3.5.1
Modular Reduction). In this case the following parameters must be additionally provided:
• N—the modulus (pointed by {nu1ModBase,u2Modlength +4})
• Cns—the reduction constant
– In case of Big reduction, Cns is pointed by {nu1CnsBase,64bytes}.
– In case of Fast or Normalized reduction, Cns is pointed by (pointed by
{nu1CnsBase,u2ModLength+ 8})
Note:
The result buffer R must first be padded with zero bytes until its length is sufficient to perform the
reduction (2*u2ModLength + 8) to be used by the Modular Reduction service as an input parameter.
The result of the reduction is written in the area X pointed by {nu1XBase, u2ModLength + 4}.
For example, if u2ModLength, u2XLength and u2YLength are 0x80 bytes, the length of the R space is
2*(u2ModLength + 4) = 0x108 bytes because of the constraints of modular reduction.
In case of Fast or Normalized Reduction, the length of the result is u2ModLength + 4 so 0x84 bytes.
Thus, the zone X has a length of 0x84 bytes (at least). The multiplication of X by Y provides a result of
length 0x100 bytes in the zone R so the 8 MSB bytes must be previously padded with zero bytes (in
offsets 0x100 to 0x107).
43.3.4.9.4 Parameters Definition
Table 43-25. Fmult 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)
Specific/Gf2n
CarryIn
Bits I – – GF(2n) Bit and
Carry In
–
Specific/
CarryOut Zero
Violation
Bits I – – – Carry Out, Zero
Bit and Violation
Bit filled
according to the
result
nu1ModBase nu1 I Crypto
RAM
u2ModLength + 4 Base of N Base of N
untouched
SAM D5x/E5x Family Data Sheet
Public Key Cryptography Controller (PUKCC)
© 2019 Microchip Technology Inc.
Datasheet
DS60001507E-page 1465