https://github.com/nymann/crackme-zed-frequency

Solution for zed-zahir's ZED-Frequency
https://github.com/nymann/crackme-zed-frequency

Last synced: 24 days ago
JSON representation

Solution for zed-zahir's ZED-Frequency

• Host: GitHub
• URL: https://github.com/nymann/crackme-zed-frequency
• Owner: nymann
• Created: 2022-04-20T14:55:46.000Z (over 2 years ago)
• Default Branch: master
• Last Pushed: 2024-07-03T07:19:25.000Z (5 months ago)
• Last Synced: 2024-10-10T18:44:23.490Z (about 1 month ago)
• Language: Python
• Homepage: https://crackmes.one/crackme/5ed17e1633c5d449d91ae68e
• Size: 17.6 KB
• Stars: 0
• Watchers: 1
• Forks: 0
• Open Issues: 3
• Metadata Files:
  • Readme: README.md

Awesome Lists containing this project

README

        
# Crackme Zed Frequency

### How to test solution

```sh

# git clone the repo, then:

docker build -t license -f docker/Dockerfile .

docker run -it license

```

Write up

```c

int main(int argc,char **argv)

{

  int character;

  FILE *key_file_stream;

  long in_FS_OFFSET;

  int i;

  int local_b4;

  uint auStack168 [28];

  char local_38 [26];

  undefined local_1e;

  long local_10;

  local_10 = *(long *)(in_FS_OFFSET + 0x28);

  if (argc < 2) {

    printf("usage: %s \n",*argv);

                    /* WARNING: Subroutine does not return */

    exit(1);

  }

  key_file_stream = fopen(argv[1],"rt");

  for (i = 0; i < 0x1a; i = i + 1) {

    // initialize the first 26 elements in the array to 0 */

    auStack168[i] = 0;

  }

  // for each character in the file

  while (character = fgetc(key_file_stream), character != -1) {

    // If character is not lowercase a to z

    if ((character < 0x61) || (0x7a < character)) {

      // If character is uppercase A to Z

      if ((0x40 < character) && (character < 0x5b)) {

        // Set austack[char - 'A'] = austack[char - 'A'] + 1 */

        auStack168[character + -0x41] = auStack168[character + -0x41] + 1;

      }

    }

    else {

      // character is lowercase [a;z]

      auStack168[character + -0x61] = auStack168[character + -0x61] + 1;

    }

  }

  printf("the generated key is: ");

  // print the first 26 characters of the generated key */

  for (local_b4 = 0; local_b4 < 0x1a; local_b4 = local_b4 + 1) {

    printf("%d",(ulong)auStack168[local_b4]);

    local_38[local_b4] = (char)auStack168[local_b4] + '0';

  }

  local_1e = 0;

  putchar(10); // Print newline character \n to stdout

  character = strcmp(local_38,"01234567890123456789012345");

  if (character == 0) {

    puts("you succeed!!");

  }

  else {

    puts("you failed!!");

  }

  if (local_10 == *(long *)(in_FS_OFFSET + 0x28)) {

    return 0;

  }

                    /* WARNING: Subroutine does not return */

  __stack_chk_fail();

}

```

So the logic goes something like this:

- Given a keyfile

- For each character in the keyfile

- If the character is alpha lowercase

  - `output[letter - 'a'] += 1`

- If the character is alpha uppercase

  - `output[letter - 'A'] += 1`

- If the character is not a letter

  - do nothing

Now the final sequence:

- For each integer in the `output` array

- `key += chr(integer + '0')`

- If the key matches "01234567890123456789012345"

  - "you succeed!!"