如何解密私钥文件并使用 C 中的 openssl 调用对一些文本进行签名？

#include <stdio.h>
#include <openssl/evp.h>
#include <openssl/pem.h>

int main() {
    // 加载私钥文件
    EVP_PKEY *private_key = NULL;
    FILE *private_key_file = fopen("private_key.pem", "r");
    if (private_key_file == NULL) {
        printf("Failed to open private key file.\n");
        return 1;
    }
    private_key = PEM_read_PrivateKey(private_key_file, NULL, NULL, NULL);
    fclose(private_key_file);
    if (private_key == NULL) {
        printf("Failed to load private key.\n");
        return 1;
    }

    // 创建签名上下文
    EVP_MD_CTX *ctx = EVP_MD_CTX_new();
    if (ctx == NULL) {
        printf("Failed to create signature context.\n");
        EVP_PKEY_free(private_key);
        return 1;
    }

    // 设置签名算法
    const EVP_MD *md = EVP_get_digestbyname("SHA256");
    if (md == NULL) {
        printf("Invalid signature algorithm.\n");
        EVP_MD_CTX_free(ctx);
        EVP_PKEY_free(private_key);
        return 1;
    }

    // 使用私钥进行签名
    if (EVP_DigestSignInit(ctx, NULL, md, NULL, private_key) != 1) {
        printf("Failed to initialize signature operation.\n");
        EVP_MD_CTX_free(ctx);
        EVP_PKEY_free(private_key);
        return 1;
    }

    // 更新签名数据
    const char *data = "Hello, world!";
    if (EVP_DigestSignUpdate(ctx, data, strlen(data)) != 1) {
        printf("Failed to update signature data.\n");
        EVP_MD_CTX_free(ctx);
        EVP_PKEY_free(private_key);
        return 1;
    }

    // 完成签名
    unsigned char signature[EVP_MAX_MD_SIZE];
    size_t signature_len;
    if (EVP_DigestSignFinal(ctx, signature, &signature_len) != 1) {
        printf("Failed to finalize signature.\n");
        EVP_MD_CTX_free(ctx);
        EVP_PKEY_free(private_key);
        return 1;
    }

    // 打印签名结果
    printf("Signature: ");
    for (size_t i = 0; i < signature_len; i++) {
        printf("%02x", signature[i]);
    }
    printf("\n");

    // 清理资源
    EVP_MD_CTX_free(ctx);
    EVP_PKEY_free(private_key);

    return 0;
}