initial

2/Basics3/README

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+Welcome to basics3!
+-----
+We encrypted the flag, but we lost our decryption routine.
+We only remember the key we used: 02723
+You will find the encryption software in your home directory.
+Can you recover the flag?
+
+
+Hints
+-----
+Code may do weird things, you don't have to understand all of it if you
+can calculate the same result or the input for some result (without knowing exactly what happens).

2/Basics3/flag.enc

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+2c 1d 5d b1 67 85 0f 52 69 93 1c 2d 79 f0 4b c2 
+64 bd 0f da 95 88 16 0c 2f 5e 9e 68 ee f4 1e b6 
+b8 a7 7d 43 a8 00 51 c4 fe 54 10 26 f1 d3 2b 

2/Basics3/test.c

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+#include <stdint.h>
+#include <stdio.h>
+#include <sys/types.h>
+
+char test[] = "hacklab{                           ";
+
+unsigned int start_key=2723;
+
+//paste flag.enc here (add ", 0x")
+char text[] = {0x2c, 0x1d, 0x5d, 0xb1, 0x67, 0x85, 0x0f, 0x52, 0x69, 0x93, 0x1c, 0x2d, 0x79, 0xf0, 0x4b, 0xc2, 0x64, 0xbd, 0x0f, 0xda, 0x95, 0x88, 0x16, 0x0c, 0x2f, 0x5e, 0x9e, 0x68, 0xee, 0xf4, 0x1e, 0xb6, 0xb8, 0xa7, 0x7d, 0x43, 0xa8, 0x00, 0x51, 0xc4, 0xfe, 0x54, 0x10, 0x26, 0xf1, 0xd3, 0x2b};
+
+typedef uint8_t byte;
+byte scramble_key(unsigned int *key_input){
+  *key_input = (*key_input * 0x41c64e6d + 0x3039) % 0x80000000;
+  return *(byte *)((long)key_input + 3) ^
+         (byte)*key_input ^ *(byte *)((long)key_input + 1) ^ *(byte *)((long)key_input + 2);
+}
+
+void encrypt(uint32_t key,char *text,ulong len)
+{
+  byte bVar1;
+  uint32_t local_1c [4];
+  int i;
+  
+  local_1c[0] = key;
+  for (i = 0; (ulong)(long)i < len; i = i + 1) {
+    bVar1 = scramble_key(local_1c);
+    text[i] = bVar1 ^ text[i];
+    text[i] = text[i] + 'O';
+  }
+  return;
+}
+void decrypt(uint32_t key,char *text,ulong len)
+{
+  byte bVar1;
+  uint32_t local_1c [4];
+  int i;
+  
+  local_1c[0] = key;
+  for (i = 0; (ulong)(long)i < len; i = i + 1) {
+    bVar1 = scramble_key(local_1c);
+    text[i] = text[i] - 'O';
+    text[i] = bVar1 ^ text[i];
+  }
+  return;
+}
+
+
+int main(int argc, char** args){
+    decrypt(start_key, text, sizeof(text));
+    for(uint8_t i=0; i<sizeof(text); i++)
+        printf("%c", text[i]);
+}