Salt
What is a 'salt' in cybersecurity?
In the context of identity and access management (IAM) and cybersecurity, a salt is a random piece of data added to user passwords before they are hashed and stored in a database. This technique significantly enhances the security of password storage, making it much harder for attackers to exploit stolen password hashes through brute force or dictionary attacks. Salting is a fundamental practice in securing sensitive authentication data, helping organisations protect user credentials from compromise.
When a user creates or updates a password, the system generates a unique salt value for that password. The salt is then combined with the password, and the resulting string is hashed using a cryptographic hashing algorithm. The hash, rather than the actual password or the salted password, is stored in the system. The salt itself is typically stored alongside the hash. When the user attempts to log in, the system retrieves the salt, applies it to the entered password, hashes the result, and compares it to the stored hash. If they match, access is granted.
What is the purpose of salt?
The primary purpose of a salt is to ensure that even if two users have identical passwords, their hashes will be different. Without salting, attackers could use precomputed hash databases, known as "rainbow tables," to quickly match hashes to their plaintext passwords. Salting renders rainbow table attacks ineffective because the salt makes every hash unique. Even with access to the salt values, an attacker must recompute hashes for every possible password and salt combination, significantly increasing the computational effort required.
Salting is particularly important for IAM systems that handle authentication for large numbers of users. If an attacker breaches a database of unsalted password hashes, they can uncover common passwords shared among users very quickly. Salting eliminates this vulnerability by making it computationally impractical to determine which users share passwords, even if the hash algorithm used is known.
To maximise the security benefits of salting, organisations must pair it with strong cryptographic practices. For example, using secure, industry-standard hashing algorithms like bcrypt, Argon2, or PBKDF2 ensures that brute-force attacks remain computationally expensive. Additionally, salts should be generated randomly for each password and have sufficient length and entropy to resist prediction or reuse.
Salting is not without its limitations. It is primarily a measure to secure passwords at rest, but it does not protect against weak or guessable passwords. Organisations must complement salting with strong password policies, user education, and additional layers of authentication, such as multi-factor authentication (MFA). Furthermore, in the event of a data breach, attackers who gain access to both the hashed passwords and their salts can still perform brute-force attacks, albeit at a slower pace.
