Question

我正在尝试创建类似shadowfile的txt文件，我正在使用crypt来生成哈希。我通过终端要求密码，我生产一个伪随机盐。我在crypt函数中给出了这两个值，但它每次都会创建一个不同的哈希值，或者根本不会创建任何哈希值，我无法得到我的代码有什么问题。

#include<stdio.h>
#include<cstdlib>
#include<iostream>
#include<fstream>
#include<ctime>
#include<crypt.h>
#include<unistd.h>


using namespace std;

/*====== READ STRING DYNAMICALLY ======*/

char* readFromTerminal() {

    int length = 0; //counts number of characters
    char c; //holds last read character
    char *input;

    input = (char *) malloc(sizeof (char)); //Allocate initial memory

    if (input == NULL) //Fail if allocating of memory not possible
    {
        printf("Could not allocate memory!");
        exit(1);
    }

    while ((c = getchar()) != '\n') //until end of line
    {
        realloc(input, (sizeof (char))); //allocate more memory
        input[length++] = c; //save entered character
    }

    input[length] = '\0'; //add terminator
    return input;
}

/*====== GENERATE PSEUDO RANDOM SALT VALUE ======*/

char* generateSalt() {

    const char alphanum[] =
            "0123456789"
            "!@#$%^&*"
            "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
            "abcdefghijklmnopqrstuvwxyz"; //salt alphanum

    int alphanumLength = sizeof (alphanum) - 1; // alphanum lenght

    char *salt; //salt string

    salt = (char *) malloc(sizeof (char)); //Allocate initial memory

    if (salt == NULL) //Fail if allocating of memory not possible
    {
        printf("Could not allocate memory!");
        exit(1);
    }

    srand(time(NULL));

    for (int i = 0; i < 21; i++) {
        realloc(salt, (sizeof (char))); //allocate more memory

        salt[i] = alphanum[rand() % alphanumLength]; //generate a random character from the alphanum
    }

    salt[21] = '\0'; //add terminator

    return salt;
}

/*====== MAIN ======*/
int main(int argc, char** argv) {

    char *username, *password, *salt, *hash;

    ofstream myshadow("myshadow.txt", ios::out);

    cout << "Enter your username: ";
    username = readFromTerminal();
    cout << "Enter your password: ";
    password = readFromTerminal();

    salt = generateSalt();
    hash = (char *) malloc(30 * sizeof (char)); //Allocate memory for hash
    hash = crypt(password, salt);

    myshadow << username << ":" << hash;
    return 0;
}

Answer 1

这里有很多需要改进的地方！

当C ++附带char *

std::string

您使用明确的malloc和realloc，让我们认为问题很快就会到来

手动内存管理需要非常谨慎的编程。错误是由realloc的错误使用引起的：size参数提供了新的总分配的大小，而不是增量。因此，您应该跟踪分配的大小，增加它并使用该新值调用realloc。由于realloc可能会返回一个新的内存块，因此您应该始终使用：

input = (char *) realloc(input, new_size);

BTW，generateSalt ...

中的等效问题

但由于std::getline，所有内容都已包含在C ++中！此外，<random>模块带有很棒的生成器，当旧的rand遭受多个默认设置时（只需谷歌搜索 rand vs. random ）

所以代码可以被删除到：

include<iostream>
#include<fstream>
#include<unistd.h>
#include <random>


using namespace std;

std::string generateSalt() {

    const char alphanum[] =
            "0123456789"
            "!@#$%^&*"
            "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
            "abcdefghijklmnopqrstuvwxyz"; //salt alphanum

    std::random_device rd;  //Will be used to obtain a seed for the random number engine
    std::mt19937 gen(rd()); //Standard mersenne_twister_engine seeded with rd()
    std::uniform_int_distribution<> dis(0, sizeof(alphanum)-1); //Uniform distribution on an interval
    char salt[22];          // 21 useful characters in salt (as in original code)
    for(char& c: salt) {
        c = alphanum[dis(gen)];
    }
    salt[21] = 0;
    return std::string(salt);
}

/*====== MAIN ======*/
int main(int argc, char** argv) {

    string username, password, salt, hash;

    ofstream myshadow("myshadow.txt", ios::out);

    cout << "Enter your username: ";
    if (! getline(cin, username)) return 1;
    cout << "Enter your password: ";
    if (! getline(cin, password)) return 1;

    salt = generateSalt();
    hash = crypt(password.c_str(), salt.c_str());

    myshadow << username << ":" << hash;
    return 0;
}

使用C ++字符串的另一个不错的副作用是自动处理分配和解除分配，无需调用free ......

c ++中的crypt返回不同的字符串（或根本没有字符串）

1 个答案: