🔐 RSA Even-N Cracker Tool

A Python tool to exploit the weak RSA case where N is even (p = 2, q = N/2). It works with local files or directly with remote CTF challenge servers (netcat-style).

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📦 Requirements

• Python 3.8+
• No external libraries (only Python standard library).

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⚙️ Usage

1. Crack from a file

python3 rsa_evenN_cracker_tool.py input.txt

The file may contain:

N=12345678901234567890
e=65537
c=98765432109876543210

or Python-style:

N = 12345678901234567890
e = 65537
c = 98765432109876543210

or with colons:

N: 12345678901234567890
e: 65537
cyphertext: 98765432109876543210

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2. Crack from a challenge server (netcat mode)

Connect to a remote challenge server like with nc host port:

python3 rsa_evenN_cracker_tool.py -n verbal-sleep.picoctf.net 53671

The tool will capture the output (e.g. N: ..., e: ..., cyphertext: ...), factor N, compute d, and print the plaintext.

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3. Output control

• Pretty output (default):

  == Case #1 ==
  N (even) = ...
  e = 65537
  q = N//2 = ...
  phi = ...
  m (int) = ...
  plaintext (utf-8): picoCTF{flag_here}
  

• Raw plaintext only (good for piping):

  python3 rsa_evenN_cracker_tool.py input.txt -r

• Escape non-UTF8 bytes:

  python3 rsa_evenN_cracker_tool.py input.txt -r -x

• Verbose (debug) mode — show the raw captured server/file text before parsing:

  python3 rsa_evenN_cracker_tool.py -n verbal-sleep.picoctf.net 53671 -v

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📝 Examples

From file

python3 rsa_evenN_cracker_tool.py encrypt.txt

Output:

== Case #1 ==
N (even) = 188548530
e = 65537
q = N//2 = 94274265
phi = 94274264
m (int) = 1122334455
plaintext (utf-8): picoCTF{tw0_1$_pr!m378257f39}

From server

python3 rsa_evenN_cracker_tool.py -n verbal-sleep.picoctf.net 53671 -r

Output:

picoCTF{flag_here}

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🚨 Limitations

• Only solves RSA when N is even (p=2).
• If N is odd (normal RSA), the script will refuse to solve.
• In netcat mode, the tool only receives data — it does not automatically send the cracked flag back to the server (you copy-paste manually).

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🔖 Flags & Options

Option	Description
file	Input file containing N/e/c values
-n host port	Connect to a challenge server (netcat mode)
-r	Print only plaintext (raw mode)
-x	Escape invalid UTF-8 characters
-v	Show raw captured text (useful for debugging parsing)

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