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RSA tool for ctf - uncipher data from weak public key and try to recover private key Automatic selection of best attack for the given public key

Attacks :

  • Weak public key factorization
  • Wiener's attack
  • Hastad's attack (Small public exponent attack)
  • Small q (q < 100,000)
  • Common factor between ciphertext and modulus attack
  • Fermat's factorisation for close p and q
  • Gimmicky Primes method
  • Past CTF Primes method
  • Self-Initializing Quadratic Sieve (SIQS) using Yafu
  • Common factor attacks across multiple keys
  • Small fractions method when p/q is close to a small fraction
  • Boneh Durfee Method when the private exponent d is too small compared to the modulus (i.e d < n^0.292)
  • Elliptic Curve Method


usage: [-h] (--publickey PUBLICKEY | --createpub | --dumpkey) [--uncipher UNCIPHER] [--verbose] [--private] [--n N] [--e E] [--ecmdigits DIGITS] [--key KEY]

Mode 1 - Attack RSA (specify --publickey)

  • publickey : public rsa key to crack. You can import multiple public keys with wildcards.
  • uncipher : cipher message to decrypt
  • private : display private rsa key if recovered

Mode 2 - Create a Public Key File Given n and e (specify --createpub)

  • n - modulus
  • e - public exponent

Mode 3 - Dump the public and/or private numbers from a PEM/DER format public or private key (specify --dumpkey)

  • key - the public or private key in PEM or DER format

Uncipher file :

./ --publickey ./ --uncipher ./ciphered\_file

Print private key :

./ --publickey ./ --private

Attempt to break multiple public keys with common factor attacks or individually - use quotes around wildcards to stop bash expansion

./ --publickey "*.pub" --private

Generate a public key :

./ --createpub --n 7828374823761928712873129873981723...12837182 --e 65537

Dump the parameters from a key:

./ --dumpkey --key ./

Factor with ECM when you know the approximate length in digits of a prime:

./ --publickey --ecmdigits 25 --verbose --private

Examples :

  •, weak_public.cipher : weak public key
  •, wiener.cipher : key vulnerable to Wiener's attack
  •, small_exponent.cipher : key with e=3, vulnerable to Hastad's attack
  •, small_q.cipher : public key with a small prime
  •, close_primes.cipher : public key with primes suceptible to fermat factorization
  • : public key with a gimmick prime
  • : public key with another vulnerability to fermat factorization
  • : public key with a prime from a past CTF
  • 256bit public key that is factored in 30 seconds with SIQS
  • a public key with a prime that is described as an expression on
  • a public key where p/q is close to a small fraction
  • a public key factorable using boneh_durfee method
  • and Public keys that share a common factor
  • Public key with a 25 digit prime factorable with ECM method in around 2 minutes (use --ecmdigits 25 to test)


MacOS-specific Instructions

If pip install -r "requirements.txt" fails to install requirements accessible within environment, the following command may work.

easy_install `cat requirements.txt`


  • Implement multiple ciphertext handling for more attacks
  • Implement support for MultiPrime RSA (see 0ctf 2016)
  • Possibly implement Msieve support...
  • Some kind of polynomial search...
  • Brainstorm moar attack types!
  • Saw a CTF where the supplied N was a 2048 bit prime. Detect this and solve using phi = (n - 1) * (n - 1) which seemed to work for that CTF
  • Pollards p-1 for relatively smooth numbers
  • Replicate all functionality of
  • Support more types of expression based primes from


RSA CTF Tool - Tool to attack RSA public keys and ciphertexts in common ways



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