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ecdhp256

Core Description

This core implements the scalar point multiplier for ECDSA curve P-384. It can be used during generation of public keys, the core can also be used as part of the signing operation, it can also do ECDH key exchange.

API Specification

The core interface is similar to other Cryptech cores. FMC memory map looks like the following:

0x0000 | NAME0
0x0004 | NAME1
0x0008 | VERSION

0x0020 | CONTROL
0x0024 | STATUS

0x0200 | K00
0x0204 | K01
...
0x022C | K11

0x0240 | XIN00
0x0244 | XIN01
...
0x026C | XIN11

0x0280 | YIN00
0x0284 | YIN01
...
0x02AC | YIN11

0x02C0 | XOUT00
0x02C4 | XOUT01
...
0x02EC | XOUT11

0x0300 | YOUT00
0x0304 | YOUT01
...
0x032C | YOUT11

The core has the following registers:

Implementation Details

The top-level core module contains block memory buffers for input and output operands and the base point multiplier, that reads from the input buffer and writes to the output buffers.

The base point multiplier itself consists of the following:

The "worker" unit can execute five basic operations:

There are two primary microprograms, that the worker runs: curve point doubling and addition of curve point to the base point. Those microprograms use projective Jacobian coordinates, so one more microprogram is used to convert the product into affine coordinates with the help of modular inversion unit.

Note, that the core is supplemented by a reference model written in C, that has extensive comments describing tricky corners of the underlying math.

Vendor-specific Primitives

Cryptech Alpha platform is based on Xilinx Artix-7 200T FPGA, so this core takes advantage of Xilinx-specific DSP slices to carry out math-intensive operations. All vendor-specific math primitives are placed under /rtl/lowlevel/artix7, the core also offers generic replacements under /rtl/lowlevel/generic, they can be used for simulation with 3rd party tools, that are not aware of Xilinx-specific stuff. Selection of vendor/generic primitives is done in ecdsa_lowlevel_settings.v, when porting to other architectures, only those four low-level modules need to be ported.

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