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我正在尝试创建一个简单的应用程序来加密和解密一个小于 10 字节的小文件。我正在使用 C 的 OpenSSL API（AES-128 ecb 加密），当我加密字符串并将其保存到文件时遇到了一个奇怪的“错误”。

unsigned char buffer[256];
unsigned char rcv[256];
char my_string[]={"123456"};

int bil = aes_encrypt(my_string, strlen(my_string), "1", NULL, buffer);

FILE* fp =fopen("encrypted_file","w");
write(fileno(fp),buffer,bil);
fclose(fp);

aes_decrypt(buffer, bil, "1", NULL, rec);

printf("%s\n",rec); /* Correct: Prints 123456 */

这里的问题是，如果我从文件中读取密文，虽然它正是我之前保存的那个，但它似乎没有被正确解密。

FILE* fp =fopen("encrypted_file","r");

int bil = read(fileno(fp),buffer,256); /* The buffer contains the exact cipher that was created by the aes_encrypt in the first place */
fclose(fp);

int y = aes_decrypt(buffer, bil, "1", NULL, rec);

printf("%s\n",rec);  /* Emptry string */

加解密函数如下图所示：

加密：

int
aes_encrypt(unsigned char *plaintext, int plaintext_len, unsigned   char *key,
unsigned char *iv, unsigned char *ciphertext){
    EVP_CIPHER_CTX* ctx;

    int len;
    int ciphertext_len;

    ctx = EVP_CIPHER_CTX_new();
    EVP_EncryptInit_ex(ctx, EVP_aes_128_ecb(), NULL, key, iv);
    EVP_EncryptUpdate(ctx, ciphertext, &len, plaintext, plaintext_len);

    ciphertext_len = len;
    EVP_EncryptFinal_ex(ctx, ciphertext + len, &len);
    ciphertext_len += len;
    EVP_CIPHER_CTX_free(ctx);
    return ciphertext_len;
}`

解密：

int
aes_decrypt(unsigned char *ciphertext, int ciphertext_len, unsigned char *key,
unsigned char *iv, unsigned char *plaintext){
    EVP_CIPHER_CTX *ctx;
    int len;
    int plaintext_len;

    ctx = EVP_CIPHER_CTX_new();
    EVP_DecryptInit_ex(ctx, EVP_aes_128_ecb(), NULL, key, iv);
    EVP_DecryptUpdate(ctx, plaintext, &len, ciphertext, ciphertext_len);

    plaintext_len = len;

    EVP_DecryptFinal_ex(ctx, plaintext + len, &len);
    plaintext_len += len;

    EVP_CIPHER_CTX_free(ctx);

    plaintext[plaintext_len] = '\0';

    return plaintext_len;
}
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