What are the advantages and disadvantages of using a rainbow table over a dictionary attack?

1 Dictionary attack

A dictionary attack is a brute-force method that tries to guess a password by using a list of common or likely words, phrases, or combinations. For example, if you want to crack the password of a user named Alice, you might try words like alice, alice123, alice1984, or alice!@#. The dictionary attack can also use variations of these words, such as changing the case, adding numbers or symbols, or using leet speak. The advantage of a dictionary attack is that it is simple and fast, as it only needs to compare the hashed password with the hashed words in the dictionary. The disadvantage is that it can miss complex or uncommon passwords that are not in the dictionary, or that use different hashing algorithms.

2 Rainbow table

A rainbow table is a precomputed table that stores the hashes and the corresponding plaintexts of a large set of possible passwords. For example, a rainbow table might contain the hashes and the plaintexts of all the passwords that are up to 8 characters long and use lowercase letters and numbers. The advantage of a rainbow table is that it can crack any password that is in the table, regardless of the hashing algorithm, by simply looking up the hash and finding the plaintext. The disadvantage is that it requires a lot of storage space and time to generate the table, and that it can be defeated by adding a random value, called a salt, to the password before hashing it.

3 Speed comparison

One of the main factors to consider when choosing between a dictionary attack and a rainbow table is the speed of cracking a password. Generally speaking, a dictionary attack is faster than a rainbow table if the dictionary is small and the password is simple or common. However, a rainbow table is faster than a dictionary attack if the dictionary is large and the password is complex or uncommon. This is because a dictionary attack has to try every word in the dictionary until it finds a match, while a rainbow table only has to look up the hash once. Of course, the speed also depends on the size of the rainbow table, the hashing algorithm, and the computing power available.

4 Storage comparison

Another factor to consider is the storage space required for each method. A dictionary attack only needs to store the dictionary file, which can be relatively small depending on the number and length of the words. A rainbow table, on the other hand, needs to store the entire table, which can be very large depending on the range and complexity of the passwords. For example, a rainbow table that covers all the passwords that are up to 8 characters long and use lowercase letters, uppercase letters, numbers, and symbols would need about 2 terabytes of storage space. Therefore, a dictionary attack is more efficient in terms of storage than a rainbow table.

5 Security comparison

The last factor to consider is the security of each method. A dictionary attack is vulnerable to password policies that enforce complexity and uniqueness, such as requiring a minimum length, a mix of characters, or a change of password every few months. A rainbow table is vulnerable to salting, which is a technique that adds a random value to the password before hashing it. This makes the hash different for each password, even if they are the same plaintext. For example, if the password is alice and the salt is 1234, the hash would be different from the hash of alice without the salt. Therefore, a rainbow table would not be able to find the plaintext for the salted hash, unless it has a separate table for each possible salt. Therefore, a dictionary attack is more secure than a rainbow table if the passwords are salted.

6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?