GnuPgbruteForce

Description

This is a simple tool to brute force GnuPG key passphrase. I tried 3 different approaches to solve this problem. The bash version, the dictionary version, and the go bruteforce version. The bash version was the first one I tried, but it was too slow, so I decided to use go. I tried to use a dictionary, but it was too big, and I was worried about the length of the password file. Finally, I used a go bruteforce version, and it worked.

Bash

In the beginning, I tried to use bash to decrypt the file. I created the generate_passwords.sh file to generate all the passwords with a maximum length of 4. It generates a file called passwords.txt with all the passwords. Then I created the decrypt.sh file to decrypt the file with the password passed as an argument.

echo "$password" | gpg --batch --yes --no-use-agent --passphrase-fd 0 -d "$encrypted_file" >/dev/null 2>/dev/null

It was slower than the go version, so I decided to use go.

Dictionary

In the dictionary folder, I downloaded some dictionaries. See in the folder for more information. In these files, I have a lot of passwords that were not useful for this problem. I made a bash script to clean the dictionary. The file is export_passwords.sh, and it is in the dictionary folder.

cd dictionary
./export_passwords.sh

It produces a file called passwords.txt with all the passwords useful. Right now it has the maximum length 4 otherwise it was too big.

This file contains the password

Then execute the dictionary.go to try to decrypt To execute it use the following commands:

go run dictionary/dictionary.go  -p=dictionary/archivo.pdf.gpg -pwdfile=dictionary/my_passwords.txt

I haven't used it because i was worried about the length of the password file, and I decided to use a brute force instead.

Go Bruteforce

This is a simple tool to brute force GnuPG key passphrase. It uses Go routines and channels to speed up the process. It was implemented with WaitGroups to wait for all the Go routines to finish.

Libraries

I tried to use a Sha256 library with "crypto/cipher" and "crypto/sha256" to decrypt directly the file, but I could not make it work, because I was missing the Nonce information. I tried to use gopenpgp, but it was slower than using "golang.org/x/crypto/openpgp" even if this library is deprecated. I tried also go-crypto, but it has a Bug, and it tells me that the password is correct even if it is wrong. To try it, there is the 'change_library' branch in this repository. It's inquisitive, and I don't know why it happens.

I used GitHub Copilot mainly to generate the comments, and I used also ChatGPT for some problems with Go routines and channels.

Usage

To run this program, you need to have installed GnuPG and Go. It has three parameters:

• p: Path to the file to decrypt.
  • Mandatory
• l: Length of the passphrase.
  • Optional
  • Default: 4
• chars: Characters to use in the brute force.
  • Optional
  • Default: "abcdefghijklmnopqrstuvwxyz"

cd bin
go run GnuPgbruteForce.go -p=cifradoAsimetrico.pdf.gpg -l=2 -chars="abcdefghijklmnopqrstuvwxyz"

Executable

The executables are in the bin folder, compiled for macOS and Linux OS. Maybe it won't work because I could not test it because I have an arch64 system. In that case, it can be compiled with the following command:

 GOOS=linux GOARCH=amd64 go build -o bin/app-amd64-linux main.go 

With GOOS and GOARCH you can specify the OS and architecture you want to compile for.

Results

The first time I found the archivo.pdf passphrase it took 1 hour and 43 minutes to find it. Then I changed the code, and I divided equally the passwords betewwn the workers, starting from a different index. This way, all the passwords with the last letters are tried much earlier. I found the password in 16 Minutes and 47 Seconds The passphrase was "sgrd"