Supported ICs

Ameba SoC	RTL8721Dx	RTL8726E	RTL8720E	RTL8730E
Supported	N	Y	Y	Y

Introduction

The ECDSA supports all curves under 256-bit. But in our ROM code, only 8 kinds of curves are supported:

SECP256K1
SECP256R1
CURVE25519
SECP192K1
SECP224K1
SECP192R1
SECP224R1
BP256R1

The ECDSA has the features of key pair generation, ECDH key agreement, signature generation, public key signature verification, and basic function.

Note

The ECDSA can be accessed by NP and AP, but if multi-cores call the API to operate the ECDSA simultaneously, it will cause ECDSA function error.
Users must implement protective measures to ensure that only one core operates ECDSA at a certain time.

ECDSA OTP

The ECDSA engine can download the private key in two ways:

The user passes the private key into the API, and the function will write the private key into the registers of ECDSA.
The ECDSA automatically downloads the ECDSA OTP key.

The OTP physical map can store two keys for ECDSA to use as private keys, which can only be accessed by ECDSA trigger and will not be tampered with or read by attackers. The premise is that the private key needs to be programmed into OTP physical map.

OTP key	Address	Size	Default	Description
ECDSA_PRI_KEY1	Physical Map 0x280	32 bytes	Each Byte 0xFF	If OTPKEY=1, load this key for ECDSA engine as private key.
ECDSA_PRI_KEY2	Physical Map 0x2A0	32 bytes	Each Byte 0xFF	If OTPKEY=2, load this key for ECDSA engine as private key.
ECDSA_PRI_KEY1_Read_Protection	Physical Map 0x366[2]	1 bit	1	0: Enable read protection for ECDSA Key1 to prevent from being read out. 1: Disable read protection for ECDSA Key1.
ECDSA_PRI_KEY1_Write_Protection	Physical Map 0x366[3]	1 bit	1	0: Enable write protection for ECDSA Key1 to prevent from being programmed to all 0 by hacker. 1: Disable write protection for ECDSA Key1.
ECDSA_PRI_KEY2_Read_Protection	Physical Map 0x366[4]	1 bit	1	0: Enable read protection for ECDSA Key2 to prevent from being read out. 1: Disable read protection for ECDSA Key2.
ECDSA_PRI_KEY2_Write_Protection	Physical Map 0x366[5]	1 bit	1	0: Enable write protection for ECDSA Key2 to prevent from being programmed to all 0 by hacker. 1: Disable write protection for ECDSA Key2.

The process of programming OTP physical map is as follows:

Generate the key.

Write the key into OTP physical map by the command efuse wraw <address> <length> <data>

Suppose this is your private key, it is displayed in the u8 type array as:

u8 key1[32]= {
0xff, 0xee, 0xdd, 0xcc, 0xbb, 0xaa, 0x99, 0x88, 0x77, 0x66, 0x55, 0x44, 0x33, 0x22, 0x11, 0x00,
0xef, 0xcd, 0xab, 0x89, 0x67, 0x45, 0x23, 0x01, 0xef, 0xcd, 0xab, 0x89, 0x67, 0x45, 0x23, 0x01
};

Using the following command to program ECDSA Key1:

efuse wraw 0x280 20 ffeeddccbbaa99887766554433221100efcdab8967452301efcdab8967452301

Use the following command to read OTP key back to check if it is written correctly. If not match, re-write it.
```
efuse rraw 0x280
```
Enable ECDSA Key Read Protection and Write Protection to prevent key exposure and tampering after the written ECDSA key is confirmed.

ECDSA Key Buffer Order

The key buffer parameter of ECDSA follows the small endian mode. For example, if the key is:

0x0123456789abcdef0123456789abcdef00112233445566778899aabbccddeeff

You need to put it into an array in u8 format, like this:

u8 key1[32]={
   0xff, 0xee, 0xdd, 0xcc, 0xbb, 0xaa, 0x99, 0x88, 0x77, 0x66, 0x55, 0x44, 0x33, 0x22, 0x11, 0x00,
   0xef, 0xcd, 0xab, 0x89, 0x67, 0x45, 0x23, 0x01, 0xef, 0xcd, 0xab, 0x89, 0x67, 0x45, 0x23, 0x01
};

At this point, the array address can be API parameter.

If you program it into OTP as ECDSA_PRI_KEY1, the memory layout is:

0x280	ff	ee	dd	cc	bb	aa	99	88	77	66	55	44	33	22	11	00
0x290	ef	cd	ab	89	67	45	23	01	ef	cd	ab	89	67	45	23	01

Usage

Enabling Clock for ECDSA Engine

Make sure that the function and clock of the ECDSA are enabled; otherwise, the function will hang.
```
RCC_PeriphClockCmd(APBPeriph_ECDSA, APBPeriph_CLOCK_NULL, ENABLE);
```
Starting ECDSA Engine Calculation

Initialize the parameters and call xxx() to start ECDSA engine calculation.