flagcapt 0.3

A tool for solving cryptographic challenges in CTFs

🛡️ Fl4gC4pt - CTF Crypto Solver & Decoder Tool

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            ╚═╝     ══════╝╚═╝  ╚═╝   ╚═════╝         ╚═════╝  ═╝  ╚═╝  ╚═╝        ╚═╝     
            ・┆✦ʚ♡ɞ✦ ┆・ Fl4gC4pt by 1DH4M ・┆✦ʚ♡ɞ✦ ┆・

Fl4gC4pt is a powerful command-line tool written in Python to help you decrypt, decode, and solve various cryptographic challenges often encountered in Capture The Flag (CTF) competitions.

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Features

• RSA decryption (manual or automatic factorization via FactorDB)
• AES decryption (CBC/ECB modes)
• XOR bruteforce and known key decryption
• Classical Ciphers: Caesar, ROT13, Vigenère
• Base64 decoding
• Binary, Hex, ASCII conversions
• Reverse strings
• Wiener Attack & Low Exponent RSA Attack

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Installation from GitHub Repository

Clone the repository:

git clone https://github.com/El-Mehdi-Dridi/Flag-Capt.git

Navigate to the flagcapt directory:

cd FlagCapt

Install the required Python packages:

pip install -r requirements.txt

⚠️ Python 3.6+ is required.

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Usage

Run the tool via CLI:

flagcapt <method> -[options]

flagcapt --help                         

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            ╚═╝     ══════╝╚═╝  ╚═╝   ╚═════╝         ╚═════╝  ═╝  ╚═╝  ╚═╝        ╚═╝     
            ・┆✦ʚ♡ɞ✦ ┆・ Fl4gC4pt by 1DH4M ・┆✦ʚ♡ɞ✦ ┆・

[*] Just Wait H4CK3R ☆.𓋼𓍊 𓆏 𓍊𓋼𓍊.☆ : 100%|██████████████████████████████████ 100%
usage: flagcapt.py [-h] [-n NUMBER] [-e EXPONENT] [-c CIPHER] [-f FILE] [-p PRIME1] [-q PRIME2] [-s SHIFT] [-k KEY] [-i IV] [-m MODE] [--low-exponent-attack] [--wiener-attack] [--bruteforce] [--prefix PREFIX] method

positional arguments:
  method                Decryption method to use. Supported methods:
                          - rsa: RSA decryption
                          - factor: Factorize a number
                          - xor: XOR decryption
                          - cesar: Caesar cipher decryption
                          - rot13: ROT13 cipher decryption
                          - aes: AES decryption
                          - base64: Base64 decoding
                          - binary: Binary to string conversion
                          - hex: Hexadecimal to string conversion
                          - ascii: ASCII to string conversion
                          - vigenere: Vigenere cipher decryption
                          - reverse: Reverse string decryption

options:
  -h, --help            show this help message and exit
  -n, --number NUMBER   Modulus (n) for RSA decryption or factorization
  -e, --exponent EXPONENT
                        Exponent for RSA decryption
  -c, --cipher CIPHER   Cipher text to decrypt
  -f, --file FILE       File containing the cipher text or RSA parameters
  -p, --prime1 PRIME1   First prime for RSA decryption
  -q, --prime2 PRIME2   Second prime for RSA decryption
  -s, --shift SHIFT     Shift value for Caesar cipher
  -k, --key KEY         Key for AES or XOR decryption
  -i, --iv IV           Initialization vector for AES decryption
  -m, --mode MODE       Mode for AES decryption (e.g., CBC, ECB)
  --low-exponent-attack
                        Perform low exponent attack on RSA
  --wiener-attack       Perform Wiener's Attack on RSA
  --bruteforce          Perform XOR brute force decryption
  --prefix PREFIX       Known prefix of the flag for XOR decryption

Common Arguments

Option	Description
-c, --cipher	Cipher text or encoded input
-k, --key	Key for AES, XOR, or Vigenère
-s, --shift	Shift for Caesar cipher
-n, --number	RSA modulus n
-e, --exponent	RSA exponent e
-p, --prime1	Prime p (for RSA)
-q, --prime2	Prime q (for RSA)
-i, --iv	Initialization vector for AES
-f, --file	Read cipher text from file
--low-exponent-attack	Low exponent RSA attack (e = 3)
--wiener-attack	Wiener attack on RSA

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Available Methods

Method	Description
rsa	Decrypt RSA using p, q, e, and cipher
factor	Get p & q from n via FactorDB
xor	XOR decryption (with key or bruteforce)
cesar	Caesar cipher decryption
rot13	ROT13 decoder
aes	AES CBC/ECB decryption
base64	Decode base64 strings
binary	Binary to string
hex	Hex to string
ascii	ASCII values to string
vigenere	Vigenère decryption
reverse	Reverse the string

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📌 Examples

RSA Decryption

Typical RSA

flagcapt rsa -e 65537 -c 15752613524540611205355101441647970957140019284625297899850 -n 37400945029259002357443060764390969896841289525047883637759
[*] Just Wait H4CK3R ☆.𓋼𓍊 𓆏 𓍊𓋼𓍊.☆ : 100%|██████████████████████████████████ 100%
[CALCULING P] 82350732498477128986705241687
[CALCULING q] 454166513090222231786915976857
[*] Flag Found [*]: Flag{Fl4g_C4pT_by_1DH4M} [*]

Wiener Attack

flagcapt rsa -n < modulus > -e <exponent> -c <cipher> --wiener-attack

Low Exponent Attack

flagcapt rsa -f rsa.txt --low-exponent-attack                                             

XOR Decryption

With known key

flagcapt xor -c "ciphertext_here" -k "key"

With known perfix

flagcapt xor -f flag.txt --prefix "prefix"

BruteForce

flagcapt  xor -f flag.txt --bruteforce 

AES Decryption

CBC mode

flagcapt  aes -c "cipher" -k "key" -i "iv" --mode CBC

ECB mode

flagcapt  aes -c "cipher" -k "key" -i "iv" --mode CBC

👨‍💻 Author

Created by 1DH4M on 04/2025