关于fread的问题

wh930603 2014-04-01 04:30:49

最近在写aes加密文件。用的是fread读取txt文件内的内容，而aes加密后会出现空字符，这样生成的加密文件就含有空字符。在解密的时候，在用fread的时候此时就会默认空字符是文档的结尾。这个如何解决？自己写个fread函数可行否？或者有更好的函数能解决这个问题？

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wh930603 2014-04-02

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谢谢上面的解答。自己确实是理解不深，学习之后，自己重新写了，已经解决问题了。

wh930603 2014-04-02

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嗯，受教了。学习到了，我自己在试试。

苍蝇①号 2014-04-01

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fread 不是可以操作二进制数据吗管它空不空呢

qq120848369 2014-04-01

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fread怎么可能以空字符为结尾呢。 AES加密是要做数据填充对齐的，加密后数据长度不变。解密后末尾的空字符应该忽略掉，对于加密字符串来说天然就被忽略了，对于二进制（可能含空字符），那可以通过一个单独的长度字段标识一下数据实际长度。

zhuobattle 2014-04-01

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引用 2 楼 wh930603 的回复:

[quote=引用 1 楼 zhao4zhong1 的回复:] 推荐使用WinHex软件查看硬盘或文件或内存中的原始字节内容。不要把 fopen("...","...");fscanf,fprintf,fgets,fgetc,fclose //读时把\r\n替换成\n，写时把\n替换成\r\n;读到\x1a就设置EOF;读写的内容当字符看待和 fopen("...","...b");fread,fwrite,fgetc,fclose //不作以上替换，遇到\x1a仍继续读;读写的内容当字节看待弄混了

fopen我是用的二进制打开的。另外因为fread读的文件是我自己fwrite写的。所以原始字节内容我知道是什么。[/quote] "aes加密后会出现空字符"你不是按照二进制数据处理的吗？哪来的字符概念，更何况哪来的空字符概念？加密后就当成二进制写入。

赵4老师 2014-04-01

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仅供参考

#pragma comment(lib, "crypt32.lib")
#pragma comment(lib, "advapi32.lib")
#define _WIN32_WINNT 0x0400
#include <stdio.h>
#include <windows.h>
#include <wincrypt.h>
#define MY_ENCODING_TYPE  (PKCS_7_ASN_ENCODING | X509_ASN_ENCODING)
#define KEYLENGTH  0x00800000
void HandleError(char *s);
//--------------------------------------------------------------------
//  These additional #define statements are required.
#define ENCRYPT_ALGORITHM CALG_RC4
#define ENCRYPT_BLOCK_SIZE 8
//   Declare the function EncryptFile. The function definition
//   follows main.
BOOL EncryptFile(
    PCHAR szSource,
    PCHAR szDestination,
    PCHAR szPassword);
//--------------------------------------------------------------------
//   Begin main.
void main(void) {
    CHAR szSource[100];
    CHAR szDestination[100];
    CHAR szPassword[100];
    printf("Encrypt a file. \n\n");
    printf("Enter the name of the file to be encrypted: ");
    scanf("%s",szSource);
    printf("Enter the name of the output file: ");
    scanf("%s",szDestination);
    printf("Enter the password:");
    scanf("%s",szPassword);
    //--------------------------------------------------------------------
    // Call EncryptFile to do the actual encryption.
    if(EncryptFile(szSource, szDestination, szPassword)) {
        printf("Encryption of the file %s was a success. \n", szSource);
        printf("The encrypted data is in file %s.\n",szDestination);
    } else {
        HandleError("Error encrypting file!");
    }
} // End of main
//--------------------------------------------------------------------
//   Code for the function EncryptFile called by main.
static BOOL EncryptFile(
    PCHAR szSource,
    PCHAR szDestination,
    PCHAR szPassword)
//--------------------------------------------------------------------
//   Parameters passed are:
//     szSource, the name of the input, a plaintext file.
//     szDestination, the name of the output, an encrypted file to be
//         created.
//     szPassword, the password.
{
    //--------------------------------------------------------------------
    //   Declare and initialize local variables.
    FILE *hSource;
    FILE *hDestination;
    HCRYPTPROV hCryptProv;
    HCRYPTKEY hKey;
    HCRYPTHASH hHash;
    PBYTE pbBuffer;
    DWORD dwBlockLen;
    DWORD dwBufferLen;
    DWORD dwCount;
    //--------------------------------------------------------------------
    // Open source file.
    if(hSource = fopen(szSource,"rb")) {
        printf("The source plaintext file, %s, is open. \n", szSource);
    } else {
        HandleError("Error opening source plaintext file!");
    }
    //--------------------------------------------------------------------
    // Open destination file.
    if(hDestination = fopen(szDestination,"wb")) {
        printf("Destination file %s is open. \n", szDestination);
    } else {
        HandleError("Error opening destination ciphertext file!");
    }
    //以下获得一个CSP句柄
    if(CryptAcquireContext(
                &hCryptProv,
                NULL,               //NULL表示使用默认密钥容器，默认密钥容器名
                //为用户登陆名
                NULL,
                PROV_RSA_FULL,
                0)) {
        printf("A cryptographic provider has been acquired. \n");
    } else {
        if(CryptAcquireContext(
                    &hCryptProv,
                    NULL,
                    NULL,
                    PROV_RSA_FULL,
                    CRYPT_NEWKEYSET))//创建密钥容器
        {
            //创建密钥容器成功，并得到CSP句柄
            printf("A new key container has been created.\n");
        } else {
            HandleError("Could not create a new key container.\n");
        }
    }
    //--------------------------------------------------------------------
    // 创建一个会话密钥（session key）
    // 会话密钥也叫对称密钥，用于对称加密算法。
    // （注: 一个Session是指从调用函数CryptAcquireContext到调用函数
    //   CryptReleaseContext 期间的阶段。会话密钥只能存在于一个会话过程）
    //--------------------------------------------------------------------
    // Create a hash object.
    if(CryptCreateHash(
                hCryptProv,
                CALG_MD5,
                0,
                0,
                &hHash)) {
        printf("A hash object has been created. \n");
    } else {
        HandleError("Error during CryptCreateHash!\n");
    }
    //--------------------------------------------------------------------
    // 用输入的密码产生一个散列
    if(CryptHashData(
                hHash,
                (BYTE *)szPassword,
                strlen(szPassword),
                0)) {
        printf("The password has been added to the hash. \n");
    } else {
        HandleError("Error during CryptHashData. \n");
    }
    //--------------------------------------------------------------------
    // 通过散列生成会话密钥
    if(CryptDeriveKey(
                hCryptProv,
                ENCRYPT_ALGORITHM,
                hHash,
                KEYLENGTH,
                &hKey)) {
        printf("An encryption key is derived from the password hash. \n");
    } else {
        HandleError("Error during CryptDeriveKey!\n");
    }
    //--------------------------------------------------------------------
    // Destroy the hash object.
    CryptDestroyHash(hHash);
    hHash = NULL;
    //--------------------------------------------------------------------
    //  The session key is now ready.
    //--------------------------------------------------------------------
    // 因为加密算法是按ENCRYPT_BLOCK_SIZE 大小的块加密的，所以被加密的
    // 数据长度必须是ENCRYPT_BLOCK_SIZE 的整数倍。下面计算一次加密的
    // 数据长度。
    dwBlockLen = 1000 - 1000 % ENCRYPT_BLOCK_SIZE;
    //--------------------------------------------------------------------
    // Determine the block size. If a block cipher is used,
    // it must have room for an extra block.
    if(ENCRYPT_BLOCK_SIZE > 1)
        dwBufferLen = dwBlockLen + ENCRYPT_BLOCK_SIZE;
    else
        dwBufferLen = dwBlockLen;
    //--------------------------------------------------------------------
    // Allocate memory.
    if(pbBuffer = (BYTE *)malloc(dwBufferLen)) {
        printf("Memory has been allocated for the buffer. \n");
    } else {
        HandleError("Out of memory. \n");
    }
    //--------------------------------------------------------------------
    // In a do loop, encrypt the source file and write to the source file.
    do {
        //--------------------------------------------------------------------
        // Read up to dwBlockLen bytes from the source file.
        dwCount = fread(pbBuffer, 1, dwBlockLen, hSource);
        if(ferror(hSource)) {
            HandleError("Error reading plaintext!\n");
        }
        //--------------------------------------------------------------------
        // 加密数据
        if(!CryptEncrypt(
                    hKey,           //密钥
                    0,              //如果数据同时进行散列和加密，这里传入一个
                    //散列对象
                    feof(hSource),  //如果是最后一个被加密的块，输入TRUE.如果不是输.
                    //入FALSE这里通过判断是否到文件尾来决定是否为
                    //最后一块。
                    0,              //保留
                    pbBuffer,       //输入被加密数据，输出加密后的数据
                    &dwCount,       //输入被加密数据实际长度，输出加密后数据长度
                    dwBufferLen))   //pbBuffer的大小。
        {
            HandleError("Error during CryptEncrypt. \n");
        }
        //--------------------------------------------------------------------
        // Write data to the destination file.
        fwrite(pbBuffer, 1, dwCount, hDestination);
        if(ferror(hDestination)) {
            HandleError("Error writing ciphertext.");
        }
    } while(!feof(hSource));
    //--------------------------------------------------------------------
    //  End the do loop when the last block of the source file has been
    //  read, encrypted, and written to the destination file.
    //--------------------------------------------------------------------
    // Close files.
    if(hSource)
        fclose(hSource);
    if(hDestination)
        fclose(hDestination);
    //--------------------------------------------------------------------
    // Free memory.
    if(pbBuffer)
        free(pbBuffer);
    //--------------------------------------------------------------------
    // Destroy session key.
    if(hKey)
        CryptDestroyKey(hKey);
    //--------------------------------------------------------------------
    // Destroy hash object.
    if(hHash)
        CryptDestroyHash(hHash);
    //--------------------------------------------------------------------
    // Release provider handle.
    if(hCryptProv)
        CryptReleaseContext(hCryptProv, 0);
    return(TRUE);
} // End of Encryptfile
//--------------------------------------------------------------------
//  This example uses the function HandleError, a simple error
//  handling function, to print an error message to the standard error
//  (stderr) file and exit the program.
//  For most applications, replace this function with one
//  that does more extensive error reporting.
void HandleError(char *s) {
    fprintf(stderr,"An error occurred in running the program. \n");
    fprintf(stderr,"%s\n",s);
    fprintf(stderr, "Error number %x.\n", GetLastError());
    fprintf(stderr, "Program terminating. \n");
    exit(1);
} // End of HandleError

wh930603 2014-04-01

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引用 1 楼 zhao4zhong1 的回复:

推荐使用WinHex软件查看硬盘或文件或内存中的原始字节内容。不要把 fopen("...","...");fscanf,fprintf,fgets,fgetc,fclose //读时把\r\n替换成\n，写时把\n替换成\r\n;读到\x1a就设置EOF;读写的内容当字符看待和 fopen("...","...b");fread,fwrite,fgetc,fclose //不作以上替换，遇到\x1a仍继续读;读写的内容当字节看待弄混了

fopen我是用的二进制打开的。另外因为fread读的文件是我自己fwrite写的。所以原始字节内容我知道是什么。

赵4老师 2014-04-01

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推荐使用WinHex软件查看硬盘或文件或内存中的原始字节内容。不要把 fopen("...","...");fscanf,fprintf,fgets,fgetc,fclose //读时把\r\n替换成\n，写时把\n替换成\r\n;读到\x1a就设置EOF;读写的内容当字符看待和 fopen("...","...b");fread,fwrite,fgetc,fclose //不作以上替换，遇到\x1a仍继续读;读写的内容当字节看待弄混了

fread函数的用法