在需要验证可信来源时，需要用到签名验签。因此，需要使用私钥加密，公钥解密，取得被加密的信息。这就会使用到私钥加密，公钥解密的场景了。

参考：
https://github.com/openssl/openssl/issues/20493
https://blog.csdn.net/wq897387/article/details/114129820

使用 openssl-1.1.1 版本，3.x版本API不一样。

#include <stdio.h>
#include <string.h>
#include <stdint.h>
#include "openssl/ssl.h"
#include "openssl/pem.h"
#include "openssl/rsa.h"
#include "openssl/bio.h"

#define ENC_PADDING_TYPE  RSA_PKCS1_PADDING

int encrypt(uint8_t *data, int len, uint8_t *out)
{
    int ret = 0;
    uint8_t buff[8192] = {0};
    RSA *rsa = NULL;
    BIO *bio = NULL;
    int len1 = 0;

    FILE *f = fopen("private.pem", "r");
    if (!f) {
        printf("Open private.pem error\n");
        return -1;
    }

    len1 = fread(buff, 1, sizeof(buff), f);
    fclose(f);

    bio = BIO_new_mem_buf(buff, len1);
    if (!bio) {
        printf("BIO_new_mem_buf error\n");
        return -1;
    }

    rsa = PEM_read_bio_RSAPrivateKey(bio, &rsa, NULL, NULL);
    if (!rsa) {
        printf("PEM_read_bio_PrivateKey error\n");
        return -1;
    }

    ret = RSA_private_encrypt(len, data, out, rsa, ENC_PADDING_TYPE);
    if (!ret) {
        printf("RSA_private_encrypt error\n");
        RSA_free(rsa);
        BIO_free_all(bio);
        return -1;
    }

    RSA_free(rsa);
    BIO_free_all(bio);
    return 0;
}

int decrypt(uint8_t *data, uint8_t *out)
{
    int ret = 0;
    uint8_t buff[8192] = {0};
    RSA *rsa = NULL;
    BIO *bio = NULL;

    FILE *f = fopen("public.pem", "r");
    if (!f) {
        printf("Open public.pem error\n");
        return -1;
    }

    fread(buff, 1, sizeof(buff), f);
    fclose(f);

    bio = BIO_new_mem_buf(buff, -1);
    if (!bio) {
        printf("BIO_new_mem_buf error\n");
        return -1;
    }

    rsa = PEM_read_bio_RSA_PUBKEY(bio, &rsa, NULL, NULL);
    if (!rsa) {
        printf("PEM_read_bio_RSA_PUBKEY error\n");
        return -1;
    }

    ret = RSA_public_decrypt(256, data, out, rsa, ENC_PADDING_TYPE);
    if (!ret) {
        printf("RSA_public_decrypt error\n");
        RSA_free(rsa);
        BIO_free_all(bio);
        return -1;
    }

    RSA_free(rsa);
    BIO_free_all(bio);
    return 0;
}

int main(int argc, char **argv)
{
    const char text[8192] = "Hello world11111111111111111";
    uint8_t enc[8192] = {0};
    uint8_t dec[8192] = {0};

    printf("Text: %s\n", text);
    encrypt(text, strlen(text), enc);

    decrypt(enc, dec);
    printf("Decrypt: %s\n", dec);
    return 0;
}

运行结果：