aes-256-cbc加密/解密密钥不起作用

Question

我做了一个简单的文件加密/解密器。它将模式和要操作的文件作为参数。加密时，它生成随机字符串并使用该字符串加密文件。解密文件时，它会提示用户输入密码，并在解密时使用该密码。

我的问题是，解密时得到的不是明文，而是胡言乱语，尽管我小心翼翼地将相同的密钥写入输入。

unsigned char constkey[] = "asd123";

非常感谢James K Polk提供的加密/解密代码！

#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <openssl/evp.h>
#include <openssl/aes.h>
#include <time.h>
#include <errno.h>

#ifndef TRUE
#define TRUE 1
#endif

#ifndef FALSE
#define FALSE 0
#endif


/* Encrypt or decrypt, depending on flag 'should_encrypt' */
void en_de_crypt(int should_encrypt, FILE *ifp, FILE *ofp, unsigned char *ckey, unsigned char *ivec) {

    const unsigned BUFSIZE=4096;
    unsigned char *read_buf = malloc(BUFSIZE);
    unsigned char *cipher_buf;
    unsigned blocksize;
    int out_len;
    EVP_CIPHER_CTX ctx;

    EVP_CipherInit(&ctx, EVP_aes_256_cbc(), ckey, ivec, should_encrypt);
    blocksize = EVP_CIPHER_CTX_block_size(&ctx);
    cipher_buf = malloc(BUFSIZE + blocksize);

    while (1) {

        // Read in data in blocks until EOF. Update the ciphering with each read.

        int numRead = fread(read_buf, sizeof(unsigned char), BUFSIZE, ifp);
        EVP_CipherUpdate(&ctx, cipher_buf, &out_len, read_buf, numRead);
        fwrite(cipher_buf, sizeof(unsigned char), out_len, ofp);
        if (numRead < BUFSIZE) { // EOF
            break;
        }
    }

    // Now cipher the final block and write it out.

    EVP_CipherFinal(&ctx, cipher_buf, &out_len);
    fwrite(cipher_buf, sizeof(unsigned char), out_len, ofp);

    // Free memory

    free(cipher_buf);
    free(read_buf);
}

int rand_string(char *str, size_t size)
{
    size_t n;
    const char charset[] = "ABCDEFGHIJKLMNOPQRSTUWVXYZO1234567890";

    for (n = 0; n < size; n++) {
        int key = rand() % (int) (sizeof charset - 1);
        str[n] = charset[key];
    }

    str[size] = '\0';
    return 0;
}

void copyfile(FILE* from, FILE* to)
{
    fseek(from, 0, SEEK_END);
    long filesize = ftell(from);
    fseek(from, 0, SEEK_SET);
    char b[2];
    long a;

    for(a=0; a<filesize; a++)
    {
        fread(b, 1, 1, from);
        fwrite(b, 1, 1, to);
    }
}

int main(int argc, char *argv[]) {

    if (argc != 3) { printf("usage: %s mode file\n", argv[0]); return 0; }

    unsigned char ivec[] = "dontusethisinput";
    FILE *fIN, *fOUT;

    if (!strcmp(argv[1],"e"))
    {
        srand(time(NULL)); /* seed random */

        char passkey[6];
        rand_string(passkey,5); /* generate random password */

        if((fIN = fopen(argv[2], "rb")) == NULL){ printf("ERROR: %s\n", strerror(errno)); return 0; }
        fOUT = fopen("tempfile", "wb+");

        en_de_crypt(TRUE, fIN, fOUT, (unsigned char*)passkey, ivec); /* encrypt the file */

        fclose(fIN);
        fclose(fOUT);

        if((fIN = fopen(argv[2], "wb+")) == NULL){ printf("ERROR: %s\n", strerror(errno)); return 0; }
        fOUT = fopen("tempfile", "rb");

        copyfile(fOUT, fIN); /* replace the file with encrypted one */

        fclose(fIN);
        fclose(fOUT);

        printf("file encrypted with key [%s]\n", passkey);
    }
    else if(!strcmp(argv[1],"d"))
    {
        char key[6];
        printf("Password: ");
        fgets(key, 6, stdin); /* prompt for the key */
        key[5] = '\0';

        if((fIN = fopen(argv[2], "rb")) == NULL){ printf("ERROR: %s\n", strerror(errno)); return 0; }
        fOUT = fopen("tempfile", "wb+");

        en_de_crypt(FALSE, fIN, fOUT, (unsigned char*)key, ivec); /* decrypt the file */

        fclose(fIN);
        fclose(fOUT);

        if((fIN = fopen(argv[2], "wb+")) == NULL){ printf("ERROR: %s\n", strerror(errno)); return 0; }
        fOUT = fopen("tempfile", "rb");

        copyfile(fOUT, fIN); /* replace the file with decrypted one */

        fclose(fIN);
        fclose(fOUT);

        printf("file decrypted with key [%s]\n",key);
    }
    else { printf("invalid mode\n"); return 0; }

    remove("tempfile");
    return 0;
}

Answer 1

我跟踪问题到密码，因为当我使用常量密码时，一切都完美无缺地工作，比如

无符号char constkey[]=“asd123”；

并将其用于加密和解密。

用正确的键长尝试。