John The Ripper FAQs

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Introduction

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John the Ripper (JTR) is a popular password cracking tool that uses various techniques, including brute force and dictionary attacks, to guess weak or easily guessed passwords. This article will provide an overview of JTR's operation mode called 'character frequency tables' along with some frequently asked questions.

How Character Frequency Tables Work

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In simple terms, character frequency tables are large collections of common characters found in a given set of plaintext strings (e.g., words from dictionaries). When you run John the Ripper on an input file containing hashes or other password representations (like MD5/SHA-256), it will use these precomputed tables to quickly rule out impossible candidates before resorting to more intensive brute-force attacks.

How Fast Is Character Frequency Tables?

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The speed at which JTR operates depends largely upon several factors:

1. Strength of the passwords being cracked: If most users choose simple or easily guessable passphrases, then character frequency tables will quickly identify them and crack their hashes in a matter of seconds.

2. Size and complexity of your wordlist(s). Larger wordlists take longer to process but may catch more complex passwords.

When To Use Character Frequency Tables

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Character frequency tables are particularly useful when:

1. You're dealing with a large number of accounts where the same weak password has been reused.

2. Your target set includes many users who tend towards using common phrases or names as their login credentials (e.g., '123456' or variations thereof).

3. Dictionary wordlists don't contain your target passwords.

Limitations Of Character Frequency Tables

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While character frequency tables can be an effective way to crack weak passwords, there are some limitations:

1. Only works on plaintexts: These methods won't work if the input data is already hashed or otherwise obfuscated.

2. Not suitable for highly complex passwords : If your users tend towards using long strings of random characters and/or special characters in their passphrases, then character frequency tables will be slow to crack them.

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In conclusion, John the Ripper's character frequency table mode is a useful tool in any penetration tester or security professional's toolkit for quickly identifying weak passwords. However, it should not replace other password cracking techniques like dictionary attacks and brute force attacks entirely; instead, these methods complement each other well depending upon your specific needs.

Remember: Always use strong unique passwords that are difficult to guess!

John the ripper faq