Datasheet

• PointABase
• PointPublicKeyGen
• AWorkBase
43.3.6.13.5 Options
The options are set by the u2Options input parameter, which is composed of:
• the mandatory windows sizes WA (window for Point A) and WB (window for Point Public Key)
• the indication of the presence of the Point Signature in system RAM
Important: Please check precisely if the Point Signature is in Crypto RAM. If this is the case
the PUKCL_ZPECCMUL_SCAL_IN_CLASSIC_RAM must not be used.
The u2Options number is calculated by an “Inclusive OR” of the options. Some Examples in C language
are:
• // Point Signature in system RAM
// The Point A window size is 3
// The Point Public Key window size is 4
PUKCL(u2Options) = PUKCL_ZPECCMUL_SCAL_IN_CLASSIC_RAM |
PUKCL_ZPECCMUL_WINSIZE_A_VAL_TO_OPT(3) |
PUKCL_ZPECCMUL_WINSIZE_B_VAL_TO_OPT(4);
• // Point Signature in the Cryptographic RAM
// The Point A window size is 2
// The Point Public Key window size is 5
PUKCL(u2Options) = PUKCL_ZPECCMUL_WINSIZE_A_VAL_TO_OPT(2) |
PUKCL_ZPECCMUL_WINSIZE_B_VAL_TO_OPT(5);
For this service, many window sizes are possible. The window sizes in bits are those of the windowing
method used for the scalar multiplying.
The choice of the window sizes is a balance between the size of the parameters and the computation
time:
• Increasing the window size increases the precomputation table size.
• Increasing the window size to the optimum reduces the computation time.
The following table details the estimated windows WA and WB optimum and possible for some curves.
Table 43-90. ZpEcDsaQuickVerify Service Estimated WA and WB Window Size
Curve Size (bits) Optimum Window size Possible Window Sizes (WA, WB) or (WB, WA)
192 5 5, 5
256 5 5, 5
384 6 5, 5
521 6 4, 5
SAM D5x/E5x Family Data Sheet
Public Key Cryptography Controller (PUKCC)
© 2019 Microchip Technology Inc.
Datasheet
DS60001507E-page 1540