What Is a Rainbow Table Attack and How to Prevent It?

Most computer systems and applications use passwords as a common authentication method. The simplest way to implement authentication is to store a list of all valid passwords for each user. The downside of this method is that if the list is compromised, the attacker will know all the user passwords.

A more common approach is to store the cryptographic hash value of the password phrase. However, most hashes are quickly calculated, so an attacker who has access to the hashes can quickly check the list of possible passwords for validity.

Hackers exploit various methods to crack passwords, and rainbow table attacks are rather frequent. In this article, we explain rainbow table attacks, why they are relevant in the current cybersecurity landscape, and how to protect against them.

What is a Rainbow Table Attack?

A rainbow table attack is an attack that tries to crack passwords using a table of common passwords (and their hashes), allowing the hacker to uncover the original password. The attacker doesn’t need to guess the password, only its hash. To crack the password, the hacker uses a rainbow table – a dictionary of plaintext passwords and their corresponding hash values.

To start the attack, the hacker needs to gain access and control over any hashed password that has been leaked. Once compromised, a rainbow attack is triggered. This usually happens when the password database is not secure enough, or the attacker gains access to Active Directory. Another reason why rainbow table attacks work is that hackers gain control through various phishing techniques to enable access to the password database that the victims have access to.

To create a rainbow table, the attacker first starts by constructing a "chain" of hash values. Initially, the hacker applies the hash function on a known value - to obtain the appropriate hash value. Then s/he searches for a matching hash value by comparing hashed values from a database with hashed values from the table. Finally, the attacker can log in to the target system using the password that corresponds to the hash value that matches.

Rainbow Table Attacks vs Brute-Force Attacks

A rainbow table utilizes fast and efficient cryptanalysis. In contrast, the brute-force attack computes the hash function of each string and compares it with the hash values from the database. The rainbow table attack eliminates this need and only computes hashes of the large set of available strings beforehand.

Brute-force attacks and rainbow table attacks have certain similarities and differences. The rainbow table attack uses fewer resources (table size), so it is quicker and more effective. In the rainbow table - everything is precomputed, so getting the hash value is not an issue (unlike with brute force). It just searches and compares in the table, because all the numbers have previously been calculated.

If the hash is matched, it doesn’t matter if the string isn’t the password itself. The hacker will be authenticated. A disadvantage of the rainbow table attack is that it needs a large storage to store the rainbow tables.

How Do Rainbow Tables Work?

The essence of the rainbow table attack is a set of hashing and reducing processes. The reduction function inverses the process, merging the hash values to their corresponding plaintexts. There are four phases in this process.

Generation - The rainbow table is created by first taking a list of possible passwords and hashing them all with the same function. The rainbow table stores the hashes and their corresponding plaintext passwords.

Reduction - The hashes already in the rainbow table are subjected to a reduction process to produce a new set of hashes. Each hash is mapped to a new value using a reduction function so that it may be used as input in the following step of the process. This process is repeated several times to produce a string of hashes.

Lookup - Hackers can extract encrypted passwords from a series of hashes using a rainbow table. They work their way back through the rainbow table's hashes, starting with the final hash in each chain, until they find one that matches the target hash.

Cracking - The target hash is produced using the plaintext password that corresponds to the hash value found. This weakness of the authentication process now gives the hacker access to the protected resources.

Risks and Consequences of Rainbow Table Attacks

Rainbow table attacks have multiple risks and consequences, and the most significant ones include:

Data breaches and theft

Simply put, cracked passwords cause data breaches by giving access to a company’s data and assets to unauthorized individuals. When the attacker gets access to the organization’s sensitive data, they can use it for identity theft, additional attacks, or lock it by encryption and ransom it. To cause further damage to the organization - the attacker can openly distribute the broken credentials or sell the means of access to the company’s network.

Reputational Damage

Cybersecurity attacks are a serious risk to a business's brand as well as its financial stability. Customers expect businesses to protect their sensitive data from fraudsters in the current digital era. A cyberattack has the potential to seriously harm a company's reputation, leading to a decline in customer confidence, bad publicity, and long-term harm to the brand. This loss of trust can result in customers switching to the competition who demonstrate better security practices. That’s why many businesses end up protecting their assets after a breach.

Malware and Ransomware Distribution

Compromised accounts can also result in malware and ransomware attacks. The hackers will gain access to an organization’s network where they can then inject ransomware. When an attacker successfully infects a computer with ransomware, a prompt will display on the screen. It will inform users that the only way to regain access to their device and data is by paying the cybercriminal a specified ransom amount. Thus, password attacks can cause broader implications for cybersecurity.

Legal and Compliance Issues

Being a victim of a rainbow table attack can cause data and financial losses, but there can also be legal consequences. Different government bodies and regulations, such as GDPR or CCPA, define strict business rules and security requirements. They include potential penalties for those who do not fulfill these security requirements. Starting in October 2024, the EU is introducing the NIS2 (Network and Information Security) Directive, and companies doing business in the EU must obey its policies.

How To Prevent Rainbow Table Attacks

Now we’ll explore the various strategies for preventing rainbow table attacks and emphasize the importance of proactive measures.

Use of Strong, Unique Passwords

Enforcing a strong password policy is the first line of defense. This means setting rules that ensure all passwords used in the system are complex and difficult to crack. A strong password typically includes a mix of uppercase and lowercase letters, numbers, and special characters. It should be long enough, ideally more than 10 characters. Encouraging regular password changes can also enhance security. In addition, you should choose a reliable password management tool.

Salting Passwords

Whenever you create or save a hashed password, it should never be created without adding  salt. This makes the secret code harder to crack. What is password salting? In short, it means adding a random sequence of characters to the password. When you create a password, for example, “tree”, the salting of the password will turn into treeEA328GHzx. When it is hashed and entered into the database, the salted passcode changes to a 32+ character string.

Implementing Stronger Hash Functions

To prevent rainbow table attacks – it is crucial to utilize secure hash functions, such as SHA-256 and Bcrypt. SHA-256 is approved and recommended by the National Institute of Standards and Technology (NIST). It generates a 256-bit hash value. Although it is slower than the previous algorithms, it’s more complex, which increases the security. You should always stay updated with the latest cryptographic standards.

Multi-Factor Authentication (MFA)

Multi-factor authentication significantly improves account security. By requiring different forms of verification, such as a text message or an authentication app, MFA ensures that knowing the password alone is not enough to gain access. This is especially effective against rainbow table attacks, as the multiple factors bring an additional obstacle for the attackers. You should opt for at least 2-factor authentication whenever possible.

Regular Security Audits

A security audit is a complete evaluation of an organization’s IT assets. This includes scanning physical devices, applications, networks, and firewalls and evaluating employee safety training. Conducting regular security audits will help identify and mitigate vulnerabilities. The recommended tools for effective security auditing include real-time vulnerability scanners and penetration detection tools (Astra Security, Palo Alto, Qualys, Symantec, etc.).

In today’s digital environment, cyber security is not only the means to protect your data and assets but also a global requirement for doing business. A rainbow table attack is a password attack in which the hacker tries to crack password hashes.

To implement rainbow table cyber security - it is crucial to undertake multiple proper security measures listed above. By integrating these strategies into your security plan, you will significantly reduce IT assets’ vulnerability to rainbow table attacks and other types of cyber threats, protecting your organization’s data and reputation