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RsaCtfTool.py — RSA attack tool for CTF challenges - recover private keys from weak public keys and/or decrypt data.

Submitted by: @import:tldr-pages·Mar 2, 2026·

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Problem

How to use the RsaCtfTool.py command: RSA attack tool for CTF challenges - recover private keys from weak public keys and/or decrypt data. More information: <https://github.com/RsaCtfTool/RsaCtfTool#usage>.

Solution

RsaCtfTool.py — RSA attack tool for CTF challenges - recover private keys from weak public keys and/or decrypt data. More information: <https://github.com/RsaCtfTool/RsaCtfTool#usage>.

Recover a private key from a public key file:

RsaCtfTool.py --publickey {{path/to/key.pub}} --private

Decrypt a file using a public key:

RsaCtfTool.py --publickey {{path/to/key.pub}} --decryptfile {{path/to/ciphered_file}}

Decrypt a specific ciphertext string:

RsaCtfTool.py --publickey {{path/to/key.pub}} --decrypt "{{ciphertext}}"

Dump RSA key components (e.g., modulus, exponent) from a key file:

RsaCtfTool.py --dumpkey --key {{path/to/key.pub}}

Run a specific attack (e.g., Fermat factorization) to recover the private key:

RsaCtfTool.py --publickey {{path/to/key.pub}} --private --attack fermat

Generate a public key from modulus (n) and exponent (e):

RsaCtfTool.py --createpub -n {{modulus}} -e {{exponent}}

Attempt all available attacks to recover the private key:

RsaCtfTool.py --publickey {{path/to/key.pub}} --private --attack all

Code Snippets

Recover a private key from a public key file

RsaCtfTool.py --publickey {{path/to/key.pub}} --private

Decrypt a file using a public key

RsaCtfTool.py --publickey {{path/to/key.pub}} --decryptfile {{path/to/ciphered_file}}

Decrypt a specific ciphertext string

RsaCtfTool.py --publickey {{path/to/key.pub}} --decrypt "{{ciphertext}}"

Dump RSA key components (e.g., modulus, exponent) from a key file

RsaCtfTool.py --dumpkey --key {{path/to/key.pub}}

Run a specific attack (e.g., Fermat factorization) to recover the private key

RsaCtfTool.py --publickey {{path/to/key.pub}} --private --attack fermat

Context

tldr-pages: common/RsaCtfTool.py

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