信息安全作业：如何暴力破解smime.p7m密钥？求推荐工具

Great question—since your instructor mentioned the key is simple (short or common), here are some tried-and-true tools tailored for brute-forcing password-protected S/MIME .p7m files, along with basic workflows to get you started:

1. OpenSSL (Built-in, No Extra Installs) #

Most Unix-like systems (and Windows via WSL or pre-built binaries) come with OpenSSL pre-installed. It can directly attempt to decrypt .p7m files, so you can wrap it in a simple shell script to iterate through password lists or brute-force short combinations.

Example script for testing a password list:

#!/bin/bash
PASSWORD_LIST="simple_passwords.txt"  # Your list of common/short passwords
INPUT_FILE="smime.p7m"
OUTPUT_FILE="decrypted_content.txt"

while read -r pass; do
    echo "Testing password: $pass"
    # Suppress error output to keep the console clean
    openssl smime -decrypt -in "$INPUT_FILE" -out "$OUTPUT_FILE" -passin pass:"$pass" 2>/dev/null
    if [ $? -eq 0 ]; then
        echo "✅ Success! Found password: $pass"
        exit 0
    fi
done < "$PASSWORD_LIST"

echo "❌ Password not found in the provided list."

For brute-forcing short numeric/alpha combinations, you can expand the script with nested loops (e.g., for 1-3 character passwords).

2. John the Ripper (Specialized Password Cracker) #

John is a widely used, open-source password cracking tool with dedicated modules for S/MIME. It’s optimized for speed and supports both wordlists and incremental brute-force modes.

Steps to use:

• First, convert your .p7m file into a format John can parse using the smime2john script (included with most John installations):

  smime2john smime.p7m > smime_hash.txt
  

• Then run John with a wordlist or brute-force mode:

  # Use a pre-made common password list
  john --wordlist=common_words.txt smime_hash.txt
  
  # Brute-force 1-4 character passwords (perfect for your instructor's "simple key" hint)
  john --incremental=All --min-length=1 --max-length=4 smime_hash.txt
  

3. Hashcat (GPU-Accelerated Speed) #

If you have a GPU, Hashcat will drastically speed up brute-force attempts. It supports S/MIME password cracking via mode 14600.

Basic workflow:

• Extract the hash from your .p7m file (you can use OpenSSL for this):

  openssl smime -decrypt -in smime.p7m -out /dev/null -passin pass:x 2>&1 | grep -oP 'salted__\K.*' | xxd -r -p > smime_hash.bin
  

• Run Hashcat with a wordlist or brute-force:

  # Use a wordlist for common passwords
  hashcat -m 14600 smime_hash.bin common_passwords.txt
  
  # Brute-force 1-4 character combinations using all printable characters
  hashcat -m 14600 -a 3 --increment --increment-min 1 --increment-max 4 smime_hash.bin ?a?a?a?a
  

Important Ethical Note #

Since this is a class assignment, you obviously have explicit permission to work with this file. But always remember: unauthorized cracking of encrypted files is illegal and unethical in any other context.

内容的提问来源于stack exchange，提问作者mihaha