Can you crack this SHA1 hash?

Solution: Crack SHA1 Hash

This challenge demonstrates various methods for cracking SHA1 hashes, a fundamental skill in password security assessment and penetration testing.

Method 1: Online Rainbow Tables

The fastest approach is using online hash databases that contain precomputed SHA1 hashes:

1. Copy the hash: 8eec7bc461808e0b8a28783d0bec1a3a22eb0821
2. Visit an online hash cracker like CrackStation (crackstation.net), HashKiller, or MD5Decrypt
3. Paste the hash into the search field
4. The service will look up the hash in its database of precomputed values
5. The plaintext will be revealed instantly if it exists in the database

Why this works: Many online services maintain massive databases of common passwords, dictionary words, and their corresponding hashes. This makes cracking common passwords nearly instantaneous.

Method 2: Hashcat (GPU Acceleration)

Hashcat is a powerful password cracking tool that leverages GPU acceleration:

1. Save the hash to a file: echo '8eec7bc461808e0b8a28783d0bec1a3a22eb0821' > hash.txt
2. Download a wordlist like rockyou.txt: wget https://github.com/brannondorsey/naive-hashcat/releases/download/data/rockyou.txt
3. Run hashcat with SHA1 mode (mode 100): hashcat -m 100 hash.txt rockyou.txt
4. Hashcat will test each word in the wordlist against the hash
5. Once cracked, view results: hashcat -m 100 hash.txt --show

Advanced options:

• Use rules to modify wordlist entries: hashcat -m 100 hash.txt rockyou.txt -r best64.rule
• Brute force with mask attack: hashcat -m 100 hash.txt -a 3 ?l?l?l?l?l?l?l?l (8 lowercase letters)
• Combine multiple wordlists: hashcat -m 100 hash.txt wordlist1.txt wordlist2.txt

Method 3: John the Ripper

John the Ripper is another popular password cracking tool:

1. Create a file with the hash in John format: echo '8eec7bc461808e0b8a28783d0bec1a3a22eb0821' > hash.txt
2. Specify the hash format and run: john --format=Raw-SHA1 --wordlist=rockyou.txt hash.txt
3. John will test dictionary words against the hash
4. View cracked password: john --show --format=Raw-SHA1 hash.txt

John's modes:

• Single crack mode: john --single --format=Raw-SHA1 hash.txt
• Incremental mode (brute force): john --incremental --format=Raw-SHA1 hash.txt
• With rules: john --wordlist=rockyou.txt --rules --format=Raw-SHA1 hash.txt

Method 4: Python Script

Create a custom Python script for dictionary attacks:

import hashlib

target_hash = '8eec7bc461808e0b8a28783d0bec1a3a22eb0821'

with open('rockyou.txt', 'r', encoding='latin-1') as f:
    for line in f:
        word = line.strip()
        hash_obj = hashlib.sha1(word.encode())
        if hash_obj.hexdigest() == target_hash:
            print(f'Password found: {word}')
            break

This script reads a wordlist and computes SHA1 for each word until finding a match.

Method 5: Command Line Tools

Use built-in tools for quick verification:

# Compute SHA1 of a word
echo -n 'testword' | sha1sum
echo -n 'testword' | openssl sha1

# Test multiple words from a file
while read word; do echo -n "$word" | sha1sum; done < wordlist.txt | grep '8eec7bc461808e0b8a28783d0bec1a3a22eb0821'

Understanding the Results

Once cracked, the plaintext reveals the original word that was hashed. This demonstrates several important security concepts:

• Weak passwords are easily cracked: Common words and passwords can be broken in seconds
• SHA1 is too fast: Modern GPUs can compute billions of SHA1 hashes per second
• No salt makes hashes vulnerable: Without unique salts, identical passwords produce identical hashes
• Rainbow tables are effective: Precomputed hash databases make common passwords instantly crackable

Security Recommendations

This challenge highlights why proper password storage is critical:

• Use bcrypt, scrypt, or Argon2 for password hashing (never SHA1, MD5, or plain SHA256)
• Always use unique random salts for each password
• Implement key stretching (multiple iterations) to slow down cracking attempts
• Enforce strong password policies requiring length and complexity
• Consider implementing password breach detection using services like Have I Been Pwned

Key Takeaway: The speed and ease of cracking this SHA1 hash demonstrates why cryptographic hash functions designed for speed are inappropriate for password storage. Always use purpose-built password hashing algorithms with configurable work factors.