The term "rainbow table" in computer science refers to a massive precomputed lookup table that's used for password cracking. The word is spelled as 'reɪnboʊ teɪbəl' using IPA phonetic transcription. The word is pronounced as "RAYN-bo ta-buhl". The first syllable of the word is pronounced with a long vowel 'e' sound, followed by a short 'a' sound in the second syllable. The word ends with an unstressed vowel sound 'əl.' The spelling of the word follows the standard English spelling patterns.
A rainbow table is a type of precomputed lookup table used in cryptography to accelerate password cracking. Designed to reverse the process of password hashing, it is an efficient method of finding the original password from its hashed representation. In simple terms, it is a massive collection of precomputed hash values for a wide range of possible passwords.
This table is constructed by sequentially hashing a set of common passwords and storing the resulting hashes in a table alongside their corresponding plaintext passwords. By utilizing a reduction function, which creates a hash back into the original password space, rainbow tables are able to cover a greater number of possible passwords.
The name "rainbow table" derives from the multi-colored nature of the hashing chains that make up these tables, resembling the colorful spectrum seen in rainbows. When a password needs to be cracked, the table is queried, and if the hash value is found, the corresponding password is immediately revealed.
Rainbow tables are particularly effective against weak passwords and unsalted hash functions, significantly reducing the time and computational power needed to crack passwords. To counteract their efficiency, security measures such as salting passwords with random data are implemented to ensure that rainbow tables are rendered useless.
Despite their potential for misuse, rainbow tables also serve as valuable tools for assessing the vulnerability of passwords and hashing algorithms, aiding in the enhancement of system security.
The word "rainbow table" has its etymology derived from the use of colorful names by the researchers who first introduced the concept. In the early 1980s, Martin Hellman and his colleagues introduced a cryptanalysis technique called "rainbow trade-off" in their research on password cracking. This technique involved creating tables of precomputed values to expedite the process of reversing cryptographic hash functions, making it easier to uncover passwords from their corresponding hashes.
Hellman, inspired by the beauty and diversity of rainbows, referred to these tables as "rainbow tables", as the concept behind them encompassed a range of colors or values within them. He found this name to be catchy and memorable, which eventually became widely adopted both in the academic and cybersecurity communities to refer to precomputed tables used for password cracking.