What is a Rainbow Table Attack?

What is a rainbow table attack?

A rainbow table attack is a method used in cryptography to crack passwords by using a precomputed table of hash values to reverse cryptographic hash functions, often for the purpose of retrieving the original plain text passwords from hash values. This is an efficient technique to perform reverse lookups and can be much faster than brute-force attacks, especially when the set of possible plaintext values is very large.

Here’s how it works:

1. Precomputation: Before carrying out an attack, an attacker generates a rainbow table, which is a large database of pairs of plain text passwords and their corresponding hash values. This process involves selecting a set of initial plaintext values, hashing them, and then reducing the hash to form a new plaintext, iteratively, to form chains of related values.
2. Storage: These chains are stored in a table, but only the starting and ending values are kept to save space. The middle values can be recomputed as needed.
3. Attack: When an attacker obtains a hash value from a secure database (e.g., during a data breach), they can use the rainbow table to look up the hash. If a match is found in the table, the chain is recomputed to find the specific plaintext value that corresponds to the hash.

Rainbow tables are especially effective against unsalted hash functions. Salting, which involves adding a random value to the password before hashing, can defend against rainbow table attacks by ensuring that even identical passwords result in different hash values, rendering precomputed tables ineffective.

Why are rainbow table attacks so fast?

Rainbow table attacks are considered fast, particularly when compared to brute-force attacks, due to their use of precomputed tables that allow for rapid lookup of hash values. Here’s a breakdown of why they are so efficient:

1. Precomputation: The core of the speed advantage comes from the fact that all the computationally intensive work of hashing possible plaintext values is done in advance, during the creation of the rainbow table. Once the table is built, it can be used repeatedly without the need for further computation of hash values.
2. Space-Time Tradeoff: Rainbow tables represent a space-time tradeoff. They use significant amounts of storage space to reduce the time complexity of finding a password that matches a given hash. By storing hashes and their corresponding plaintexts, they eliminate the need to compute hashes in real time during the attack.
3. Reduced Hash Computations: In a brute-force attack, the attacker must hash each candidate password at the time of the attack. In contrast, with rainbow tables, these hashes are already computed and stored. When an attacker needs to crack a password, they simply look for the hash in the rainbow table and retrieve the corresponding plaintext.
4. Chain Reduction: Rainbow tables use a technique involving chains of hash and reduction functions to further reduce the size of the table. The reduction function maps hash values back to a possible plaintext, creating a chain that reduces storage requirements. During the attack, the attacker only needs to regenerate the part of the chain relevant to the hash they are trying to crack, which speeds up the process.
5. Lookup Speed: Modern computing hardware and optimized search algorithms make it very quick to search large datasets, such as those stored in rainbow tables. These tables are often structured to allow fast retrieval, such as using sorted lists, hash tables, or indexed databases.

While rainbow table attacks are fast and efficient for certain scenarios, they are less effective or impractical against systems that use strong salting techniques and advanced hashing algorithms, as each password requires a uniquely generated table.

What’s the difference between a brute force attack and a rainbow table attack?

Brute force attacks and rainbow table attacks are both methods used to crack passwords, but they employ different strategies and have distinct characteristics. Here’s a breakdown of the key differences:

1. Methodology:
   • Brute Force Attack: This method involves systematically attempting every possible password combination until the correct one is found. It generates each password candidate on the fly and hashes it to see if it matches the hash of the target password.
   • Rainbow Table Attack: Instead of generating passwords during the attack, this method uses precomputed tables of hashes and their corresponding plaintexts. These tables allow the attacker to look up a hash directly and find out what plaintext generates that hash, provided the plaintext is included in the table.
2. Preparation Time:
   • Brute Force Attack: There is no preparation time involved as each guess is generated and tested in real time.
   • Rainbow Table Attack: Significant time and computational resources are required initially to create the rainbow tables. However, once the tables are created, they can be used repeatedly to crack passwords more quickly.
3. Resource Usage:
   • Brute Force Attack: Requires more computational power during the attack as it needs to compute hashes for each password guess. This can be very resource-intensive, especially for strong passwords.
   • Rainbow Table Attack: Requires substantial storage space to keep the rainbow tables. The computational load during the attack is reduced because the hash calculations have already been done.
4. Effectiveness Against Salting:
   • Brute Force Attack: Salting (adding random data to the password before hashing) does not significantly hinder brute force attacks, as each attempt is hashed with the salt. The attacker only needs to adjust their method to include the salt.
   • Rainbow Table Attack: Salting effectively counters rainbow table attacks, as the addition of unique salts to each password requires a separate rainbow table for each salt, making the method impractical due to the enormous size of the required tables.
5. Speed of Attack:
   • Brute Force Attack: Generally slower than a rainbow table attack because it involves hashing every potential password at the time of the attack. The speed can vary significantly based on the complexity and length of the password.
   • Rainbow Table Attack: Typically faster for cracking a password once the table is ready, due to the rapid lookup capabilities.
6. Practicality:
   • Brute Force Attack: More universally applicable as it does not rely on precomputed values and can be used in any scenario, including against salted hashes.
   • Rainbow Table Attack: Best suited for unsalted hashes and scenarios where storage space is not a limiting factor. Less practical as security measures improve and use of salts becomes more common.

Both types of attacks highlight the importance of using strong, unique passwords and incorporating additional security measures like salting and using robust hashing algorithms to protect user data.

How can NAC help to stop a rainbow table attack?

Network Access Control (NAC) can play a crucial role in preventing rainbow table attacks, but it does so indirectly by enhancing the overall security posture of a network rather than directly interfering with the mechanics of a rainbow table attack.

Here’s how NAC can help:

1. Device Authentication and Authorization:
   • NAC systems ensure that only authorized devices can connect to the network. By requiring that each device authenticate before gaining access, NAC can prevent unauthorized devices, potentially controlled by attackers, from connecting to the network and using it as a platform to launch a rainbow table attack against other systems on the network.
2. Segmentation and Access Restrictions:
   • NAC can be used to segment the network and restrict access to sensitive systems and data. By limiting which parts of the network each user or device can access, NAC reduces the potential attack surface. This means that even if an attacker gains access to one part of the network, critical systems and data, such as password databases, may remain inaccessible.
3. Enforcement of Security Policies:
   • NAC systems enforce security policies across the network. This can include the requirement for strong, complex passwords and regular password changes, which make passwords harder to crack using rainbow tables. Additionally, NAC can enforce the use of password hashing techniques that include salts, significantly diminishing the effectiveness of rainbow tables.
4. Detection of Anomalous Behavior:
   • Many NAC solutions have the capability to monitor network traffic and identify unusual patterns that might indicate an ongoing attack, including the excessive access or transfer of data that might suggest someone is trying to steal a password database for later attack using a rainbow table.
5. Integration with Other Security Solutions:
   • NAC often integrates with other security solutions like intrusion detection systems (IDS), intrusion prevention systems (IPS), and security information and event management (SIEM) systems. This integration allows for a coordinated response to potential security threats, including those that might involve the extraction and cracking of password hashes.

By controlling access to the network and monitoring for suspicious activity, NAC helps maintain a high level of security and reduces the risk of internal and external threats, including those posed by attackers using techniques like rainbow table attacks.