What is a Rainbow Table Attack

Michelle Wilson - March 22, 2023

Everyone uses passwords as a method to secure their online accounts, but unfortunately, there are various methods that hackers can use to break them. According to public data, the rainbow table attack is one of the most efficient techniques hackers use to crack passwords. In fact, according to one study, over 50% of hashed passwords can be cracked using a rainbow table attack.

So what is it? How does it work? And what can you do to avoid the deadly rainbow table attack?

Explanation of What a Rainbow Table Is

A rainbow table contains precomputed hash values that crack password hashes. For context, a hash is a mathematical function that takes an input (a password) and returns a fixed-size string of characters. Passwords are stored as hashes in databases and other systems to protect them from being read or intercepted. People also use rainbow tables to speed up the process of cracking password hashes by precomputing many hashes and storing them in a table.

A Rainbow Table Attack, In Action

The process of a rainbow table attack involves several steps, each critical to the attack’s success.

Step 1: Generation

During a rainbow table attack, the initial step involves creating a list of potential passwords. Then, a hash function is applied to each password to generate a list of hashes. The hash function used in this step is a one-way function that takes an input, such as a password, and produces a fixed-size output, called a hash value. The output is unique to the input, meaning that even a small change in the input results in a vastly different output.

Once attackers generate hash values for potential passwords, they can store the corresponding plaintext passwords in the rainbow table and their hash values. This table is a crucial element in the rainbow table attack since it provides a precomputed database of hash values that attackers can use to crack passwords more quickly than other methods. The attackers can increase their chances of success in cracking passwords by including more passwords in the table. Attackers can use various techniques to generate large rainbow tables, such as using common passwords or complying with specific password policies.

Step 2: Reduction

In the reduction step, an attacker takes each hash in the rainbow table to use in a reduction function, which maps each hash to a new value. The new value then serves as the starting point for the next iteration. This process occurs multiple times, generating a chain of hashes between 1,000 and 10,000. The reduction function creates a deterministic sequence of hashes that an attacker can compute in reverse. The reverse step is crucial since the ultimate goal of the rainbow table attack is to recover plaintext passwords from the hash values. By generating a chain of hashes, the rainbow table reduces the number of possible plaintext passwords that an attacker must check to find a match.

The number of iterations performed in the reduction step determines the length of the chain of hashes. Longer chains require more storage space but also increase the likelihood of finding a match between the target hash and the plaintext password.

Step 3: Lookup

The third step is lookup, where a hacker can use the rainbow table to find the corresponding plaintext passwords when they have a list of hashes. They perform a reverse lookup of the hashes in the rainbow table, starting with the last hash in each chain and following the chain of hashes backwards until they find a match with the target hash.

Step 4: Cracking

The final step is cracking, where the hacker gains access to the victim’s account using the plaintext password in the rainbow table. The hacker can log into someone else’s account and access sensitive information through authentication. To defend against a rainbow table attack, it is essential to use strong and unique passwords, enable two-factor authentication, and use slow hashing functions and salted hashes to make it difficult for hackers to generate rainbow tables.

Examples of a Rainbow Table Attack

A hacker can carry out a rainbow table attack by exploiting several methods to gain unauthorized access to hashes.

A Company With Poor Login Data

One way is finding a company or a web application that uses poor login data hashing techniques and overall security. In this scenario, the attacker gains access to the database and steals the stored hashes to use the rainbow table and crack them.

A Vulnerable Active Directory

Another method involves identifying vulnerabilities in a company’s Active Directory and gaining access to the password hashes. In this case, the attacker steals the hashes and uses a rainbow table attack to crack them.

A Clever Use of Social Engineering

Furthermore, attackers can use social engineering techniques to trick users into revealing their passwords, which can be hashed and subjected to a rainbow table attack.

Prevention and Mitigation Against a Rainbow Table Attack

Using Strong Passwords

One way to prevent attacks is by implementing best practices for password protection. Complex passwords are at least 12 characters long, and combining numbers, upper and lowercase letters and symbols can significantly reduce the risk of password breaches. It’s also crucial to use unique passwords for each account, avoid common or easily guessable passwords, enable two-factor authentication, and regularly change passwords to prevent reusing old ones. These practices can make it more difficult for cybercriminals to crack passwords, reducing the likelihood of a successful attack.

Use Salting

In addition to prevention, it’s also essential to have mitigation techniques to defend against attacks like rainbow table attacks. One effective mitigation technique is using strong hashing algorithms and salting to make it more challenging for attackers to crack hashed passwords.

Salted hashes can help prevent rainbow table attacks because they make it more difficult for attackers to use precomputed tables. In a salted hash, a random string of data, known as a salt, is added to the password before it receives a hash. The hash value is unique to the password and the salt. Because the salt is unique for each password, attackers cannot use precomputed tables to crack the passwords. Instead, they would need to generate a new rainbow table for each salt value, which is impractical and time-consuming.

Regular Monitoring and Education

Additionally, companies should monitor their systems for unusual activity and implement intrusion detection systems to detect and prevent attacks. Regular security audits and employee training can also help identify vulnerabilities and ensure everyone is aware of best practices for password protection and other security measures. By combining prevention and mitigation techniques, individuals and companies can significantly reduce the risk of cyberattacks and protect sensitive data.

Conclusion

A rainbow table attack is a serious threat to password security that fraudulent parties can use to crack hashed passwords relatively quickly. It is crucial to protect against such attacks by implementing strong password policies, such as using complex and unique passwords, enabling two-factor authentication, and regularly changing passwords. Additionally, using secure hashing algorithms and salted hashes can make it even more difficult for attackers to use precomputed tables.

By taking these measures, individuals can greatly reduce the risk of falling victim to a rainbow table attack and protect sensitive information from unauthorized access.