Rainbow Table
A rainbow table
is a listing of all possible plaintext permutations of encrypted passwords
specific to a given hash algorithm.
Rainbow tables
are often used by password cracking software for network security attacks. All
computer systems that require password-based authentication store databases of
passwords associated with user accounts, typically encrypted rather than
plaintext as a security measure.
Once an
attacker gains access to a system’s password database, the password cracker
compares the rainbow table’s pre-compiled list of potential hashes to hashed
passwords in the database. The rainbow table associates plaintext possibilities
with each of those hashes, which the attacker can then exploit to access the
network as an authenticated user.
Rainbow tables
make password cracking much faster than earlier methods, such as brute-force
cracking and dictionary attacks. Depending on the particular software, rainbow
tables can be used to crack 14-character alphanumeric passwords in about 160
seconds. However the approach uses a lot of RAM
due to the large amount of data in such a table.
Rainbow tables
have only become viable recently because the amount of available RAM in older
computers was inadequate. A single rainbow table for a standard alphanumeric
file is close to 4 gigabytes (GB). Adding symbols to the mix increases the
amount of memory required, as does each step up in encryption.
To protect
against attacks using rainbow tables, system administrators should add security
measures to password encryption, such as the addition of randomly generated
characters (salt) to password hashes and avoiding the use of outdated
password hashing algorithms.
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