c语言EVPBytesToKey算法加密和解密过程使用sha256 迭代次数100次给出注释

/* 以下是C语言中EVPBytesToKey算法加密和解密过程，使用SHA256散列算法，迭代次数为100次 */

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

void main() { /* 设置需要加密的明文和秘钥 */ char *plaintext = "This is a plaintext."; char *key = "This is a key.";

/* 设置散列算法为SHA256 */
const EVP_MD *md = EVP_sha256();

/* 设置迭代次数为100 */
int iterations = 100;

/* 设置加密的密文和密文长度 */
unsigned char ciphertext[2048];
int ciphertext_len;

/* 设置解密的明文和明文长度 */
unsigned char decryptedtext[2048];
int decryptedtext_len;

/* 设置salt和iv（初始化向量） */
unsigned char salt[8] = { 0 };
unsigned char iv[16] = { 0 };

/* 调用EVP_BytesToKey函数进行密钥派生 */
EVP_BytesToKey(md, EVP_aes_256_cbc(), salt, (unsigned char *)key, strlen(key), iterations, ciphertext, iv);

/* 输出派生后的密钥 */
printf("Derived key: ");
for (int i = 0; i < EVP_CIPHER_key_length(EVP_aes_256_cbc()); i++) {
    printf("%02x", ciphertext[i]);
}
printf("\n");

/* 使用AES-256-CBC算法进行加密 */
EVP_CIPHER_CTX *ctx;
ctx = EVP_CIPHER_CTX_new();
EVP_EncryptInit_ex(ctx, EVP_aes_256_cbc(), NULL, ciphertext, iv);
EVP_EncryptUpdate(ctx, ciphertext, &ciphertext_len, (unsigned char *)plaintext, strlen(plaintext));
EVP_EncryptFinal_ex(ctx, ciphertext + ciphertext_len, &ciphertext_len);
EVP_CIPHER_CTX_free(ctx);

/* 输出加密后的密文 */
printf("Ciphertext: ");
for (int i = 0; i < ciphertext_len; i++) {
    printf("%02x", ciphertext[i]);
}
printf("\n");

/* 使用AES-256-CBC算法进行解密 */
ctx = EVP_CIPHER_CTX_new();
EVP_DecryptInit_ex(ctx, EVP_aes_256_cbc(), NULL, ciphertext, iv);
EVP_DecryptUpdate(ctx, decryptedtext, &decryptedtext_len, ciphertext, ciphertext_len);
EVP_DecryptFinal_ex(ctx, decryptedtext + decryptedtext_len, &decryptedtext_len);
EVP_CIPHER_CTX_free(ctx);

/* 输出解密后的明文 */
printf("Decrypted text: %s\n", decryptedtext);