CrackMe4

🔍 CrackMe4 – Reverse Engineering Writeup

⬇️ Download Analyzed File

🧩 Objective

Analyze the binary crackme4 to identify the correct password and understand the program’s logic.

🧪 Step 1: Initial Disassembly with objdump

objdump -d crackme4 | grep -A10 strcmp

We locate a call to strcmp@plt, indicating string comparison for password checking:

4006d5: call 400520 <strcmp@plt>
4006da: test %eax,%eax
4006dc: jne  4006ea <compare_pwd+0x70>

🧪 Step 2: Attempt to Run the Binary

ltrace ./crackme4

Initially failed due to missing permissions:

Can't execute `./crackme4': Permission denied

✅ Step 3: Grant Execute Permission

chmod +x crackme4

🧪 Step 4: Run with No Argument

ltrace ./crackme4

Output shows:

Usage : ./crackme4 password
This time the string is hidden and we used strcmp

🧪 Step 5: Run with Incorrect Password

ltrace ./crackme4 test123

Output:

strcmp("my_m0r3_secur3_pwd", "test123") = -7
printf("password \"test123\" not OK")

🎯 Step 6: Run with Correct Password

ltrace ./crackme4 my_m0r3_secur3_pwd

Output:

strcmp("my_m0r3_secur3_pwd", "my_m0r3_secur3_pwd") = 0
puts("password OK")

✅ Final Confirmation

./crackme4 my_m0r3_secur3_pwd

Result:

password OK

🧠 Conclusion

• 🔐 Correct Password: my_m0r3_secur3_pwd
• 🛠 Tools Used: objdump, ltrace, chmod
• 🧠 Skills Applied: Static + Dynamic Analysis, Binary Inspection