stm32上的rsa加密

在STM32上进行RSA加密需要用到数学计算，因此需要使用一些数学库。下面是一个使用Mbed TLS库进行RSA加密的示例代码：

#include "mbedtls/rsa.h"
#include "mbedtls/pk.h"
#include "mbedtls/entropy.h"
#include "mbedtls/ctr_drbg.h"
#include "mbedtls/error.h"

#define PUBLIC_KEY \
    "-----BEGIN PUBLIC KEY-----\n" \
    "MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEA2ZpBzgeA+c3qKdC2Rz/g\n" \
    "l70e1x3H4CE1hO9Y2IYJv1zJ1L51yCgXDWlZjY4Ov6y3E3xNzn8V+XcO0g6g1Ll6\n" \
    "NVzQmEa4z2YHx2fkvE0k6mZ4n28L/8JqT4yJx5dC+QFjR1GC4W3tqzAI9TnBdX5m\n" \
    "yVzvNTXl2CGq3dJ4UfLJiJmL3hXtC7YdL6kQkKoQll7WJZ1vO/syD4yXzt4/4e74\n" \
    "zf4fJ+3rK3x3jRSkF9klzXs6fVYdJ7vBw8mVhJ3k6UfNQ9O6uR5H8OjJGdRdQ3R5\n" \
    "0uVzqRJFgCj5mijN6AKI3qPb8y5a5lXHhJYU+IR3G9DhZ9v5a8QIv5O3vMqF9h5C\n" \
    "uQIDAQAB\n" \
    "-----END PUBLIC KEY-----\n"

int main(void)
{
    int ret;

    // 初始化随机数生成器
    mbedtls_entropy_context entropy;
    mbedtls_entropy_init(&entropy);
    mbedtls_ctr_drbg_context ctr_drbg;
    mbedtls_ctr_drbg_init(&ctr_drbg);
    const char *pers = "rsa_genkey";
    mbedtls_ctr_drbg_seed(&ctr_drbg, mbedtls_entropy_func, &entropy, (const unsigned char *)pers, strlen(pers));

    // 解析公钥
    mbedtls_pk_context pk;
    mbedtls_pk_init(&pk);
    ret = mbedtls_pk_parse_public_key(&pk, (const unsigned char *)PUBLIC_KEY, strlen(PUBLIC_KEY) + 1);
    if (ret != 0) {
        printf("mbedtls_pk_parse_public_key returned -0x%x\n", -ret);
        return 1;
    }

    // 生成随机数作为加密的明文
    unsigned char plain_text[16];
    mbedtls_ctr_drbg_random(&ctr_drbg, plain_text, sizeof(plain_text));

    // 加密
    unsigned char cipher_text[128];
    mbedtls_rsa_context *rsa = mbedtls_pk_rsa(pk);
    ret = mbedtls_rsa_pkcs1_encrypt(rsa, mbedtls_ctr_drbg_random, &ctr_drbg, MBEDTLS_RSA_PUBLIC, sizeof(plain_text), plain_text, cipher_text);
    if (ret != 0) {
        printf("mbedtls_rsa_pkcs1_encrypt returned -0x%x\n", -ret);
        return 1;
    }

    // 输出加密结果
    printf("Plain text: ");
    for (int i = 0; i < sizeof(plain_text); i++) {
        printf("%02x ", plain_text[i]);
    }
    printf("\nCipher text: ");
    for (int i = 0; i < mbedtls_rsa_get_len(rsa); i++) {
        printf("%02x ", cipher_text[i]);
    }
    printf("\n");

    // 清理
    mbedtls_pk_free(&pk);
    mbedtls_ctr_drbg_free(&ctr_drbg);
    mbedtls_entropy_free(&entropy);

    return 0;
}

其中，`PUBLIC_KEY`是RSA公钥的PEM格式字符串。首先需要初始化随机数生成器，然后解析公钥。生成随机数作为明文，然后调用`mbedtls_rsa_pkcs1_encrypt()`函数进行加密。加密后的密文长度与RSA密钥长度相等。最后清理使用的资源。