Blog | G5 Cyber Security

Fastest SHA1 Hash Finder

G5 Cyber Security

TL;DR

Instead of trying random strings (brute-force), we’ll use a precomputed rainbow table to quickly find the input that produces a specific SHA1 hash. This is much faster for common hashes, but requires storage space for the table.

How it Works

A rainbow table stores precalculated SHA1 hashes and their corresponding inputs. When you have a target hash, you look it up in the table to find its original input. If found, you’ve cracked it! If not, brute-force is still an option but less likely needed.

Step-by-step Guide

  1. Choose or Create a Rainbow Table: Rainbow tables come in different sizes and coverage (the range of possible inputs they cover). Larger tables are more effective but take up more space. You can find pre-made tables online, or create your own using tools like Hashcat (see Step 5 for details).
  2. Install a Rainbow Table Lookup Tool: Tools like John the Ripper and Hashcat can efficiently search rainbow tables. 
    sudo apt install john # Example on Debian/Ubuntu
  3. Load the Rainbow Table into the Tool: The exact command depends on the tool. For John the Ripper: 
    john --format=sha1 rainbow_table.bin  # Replace rainbow_table.bin with your table's filename
  4. Run the Lookup: Provide the target SHA1 hash to the tool. 
    john --format=sha1 --wordlist=hash_to_crack.txt #Replace hash_to_crack.txt with a file containing your hashes, one per line

    Or directly on the command line:

    echo "your_target_hash" | john --format=sha1 -
  5. (Optional) Create Your Own Rainbow Table (Advanced): If you need to crack hashes not covered by existing tables, create your own. Hashcat is a powerful tool for this: 
    hashcat -m 0 rainbow_table.bin ?a?a?a?a?a?a  # Creates a table with 6-character alphanumeric passwords

    -m 0 specifies SHA1 hash type, and the ‘?’ characters define the password space.

  6. Interpret Results: If the tool finds a match, it will display the original input (password) that generated the target hash. If no match is found, the hash wasn’t in the table.

Important Considerations

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