Datasheet

43.3.6.6.9 Status Returned Values
Returned Status Importance Meaning
PUKCL_OK – The computation passed without problem.
43.3.6.7 Projective to Affine Coordinates Conversion
43.3.6.7.1 Purpose
This service is used to perform a point coordinates conversion from projective representation to affine.
43.3.6.7.2 How to Use the Service
43.3.6.7.3 Description
The operation performed is:

  
=

Pr    

 Pr 
2

  
=

 Pr 

 Pr 
3
In this computation, the following parameters need to be provided:
• A the input point is filled in projective coordinates (X,Y,Z) or affine coordinates for X and Y, and
setting Z to 1(pointed by {nu1PointABase,3*u2ModLength + 12}). The Point A can be the point at
infinity. In this case, the u2Status returned is PUKCL_POINT_AT_INFINITY.
• Cns the Fast Modular Constant filled (pointed by {nu1CnsBase,u2ModLength +8})
• P the modulus filled (pointed by {nu1ModBase,u2ModLength +4})
• The workspace not initialized (pointed by {nu1WorkSpace, 4*u2ModLength +48}
The result is the point A with its (X,Y) coordinates converted to affine, and the Z coordinate set to 1. The
service for this operation is ZpEcConvProjToAffine.
Important: Before using this service, ensure that the constant Cns has been calculated with
the Setup of the fast Modular Reductions service.
43.3.6.7.4 Parameters Definition
Table 43-77. ZpEccConvAffineToProjective Service Parameters
Parameter Type Direction Location Data Length Before
Executing the
Service
After Executing
the Service
nu1ModBase nu1 I Crypto
RAM
u2ModLength + 4 Base of
modulus P
Base of modulus
P
nu1CnsBase nu1 I Crypto
RAM
u2ModLength + 8 Base of Cns Base of Cns
u2ModLength u2 I – – Length of
modulus P
Length of
modulus P
SAM D5x/E5x Family Data Sheet
Public Key Cryptography Controller (PUKCC)
© 2019 Microchip Technology Inc.
Datasheet
DS60001507E-page 1524