nouveau challenges

rootme/challenges/cryptanalyse/code-pseudo-random-number-generator/random_generator/crypt.c

@@ -0,0 +1,93 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <time.h>
+
+#define KEY_SIZE 32
+#define BUFF_SIZE 1024
+
+unsigned int holdrand = 0;
+
+static void Srand (unsigned int seed) {
+  holdrand = seed;
+}
+
+static int Rand (void) {
+  return(((holdrand = holdrand * 214013L + 2531011L) >> 16) & 0x7fff);
+}
+
+char* genere_key(void) {
+  int i;
+  static char key[KEY_SIZE+1];
+  const char charset[] = 
+    "abcdefghijklmnopqrstuvwxyz"
+    "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
+    "123456789";
+  
+  for(i = 0; i < KEY_SIZE; i++) {
+    key[i] = charset[Rand() % (sizeof(charset) - 1)];
+  }
+  key[KEY_SIZE] = '\0';
+
+  return key;
+}
+
+void crypt_buffer(unsigned char *buffer, size_t size, char *key) {
+  size_t i;
+  int j;
+
+  j = 0;
+  for(i = 0; i < size; i++) {
+    if(j >= KEY_SIZE)
+      j = 0;
+    buffer[i] ^= key[j];
+    j++;
+  }
+}
+
+void crypt_file(FILE *in, FILE *out) {
+  unsigned char buffer[BUFF_SIZE];
+  char *key;
+  size_t size;
+
+  key = genere_key();
+
+  printf("[+] Using key : %s\n", key);
+
+  do {
+    size = fread(buffer, 1, BUFF_SIZE, in);
+    crypt_buffer(buffer, size, key);
+    fwrite(buffer, 1, size, out);
+
+  }while(size == BUFF_SIZE);  
+}
+
+int main(int argc, char **argv) {
+  char path[128];
+  FILE *in, *out;
+
+  Srand(time(NULL));
+
+  if(argc != 2) {
+    printf("[-] Usage : %s <file>\n", argv[0]);
+    return EXIT_FAILURE;
+  }
+
+  snprintf(path, sizeof(path)-1, "%s.crypt", argv[1]);
+
+  if((in = fopen(argv[1], "r")) == NULL) {
+    perror("[-] fopen (in) ");
+    return EXIT_FAILURE;
+  }
+
+  if((out = fopen(path, "w")) == NULL) {
+    perror("[-] fopen (out) ");
+    return EXIT_FAILURE;
+  }
+
+  crypt_file(in, out);
+
+  printf("[+] File %s crypted !\n", path);
+  printf("[+] DONE.\n");
+  return EXIT_SUCCESS;
+}