TL;DR:
Password salting is a security method that strengthens password protection by adding unique, random data (a "salt") to a password before it is hashed. This ensures that every password hash stored in a database is unique, effectively defending against attacks that use precomputed tables, such as rainbow table attacks.
Salting in security is the practice of adding unique, random data (a "salt") to each user's password before it is hashed and stored. The technical workflow involves generating a cryptographically secure random salt, combining it with the user's input, and hashing the pair to create a unique digital fingerprint for future verification. This method improves security by neutralizing rainbow table attacks, protecting duplicate passwords from sharing the same hash, and forcing attackers to crack accounts individually. For robust implementation, best practices require using unique per-user salts of at least 16 bytes paired with modern algorithms and defense-in-depth techniques like peppering.
Salting is a security technique that adds unique, random data to a password before hashing to ensure every stored credential has a unique digital fingerprint.
There are 5 steps in this technical workflow:
Step 1: Generating the Salt
Step 2: Combining Password and Salt
Step 3: Hashing the Combined String
Step 4: Storing the Salt and Hash
Step 5: User Verification
Step 1: Generating the Salt
Use a Cryptographically Secure Random Number Generator (CSPRNG) to create a unique, random string for each user account. This ensures the salt is unpredictable and statistically unique, preventing attackers from using precomputed data across different users.
Step 2: Combining the Password and Salt
Combine the random salt with the user’s plain-text password by prepending or appending the salt string to the password. This combination creates a unique input for the hashing function, even if the password itself is common.
Step 3: Hashing the Combined String
Process the combined salt-password string through a one-way, memory-hard hashing function such as Argon2id, bcrypt, or scrypt. This transformation produces a fixed-length salted hash that is computationally expensive to reverse or brute-force. You can see how different algorithms handle this by using our Password Hash Generator.
Step 4: Storting the Salt and Hash
Save both the resulting salted hash and the plain-text salt in the user’s database record. The salt does not need to be encrypted or hidden. Its primary function is to provide the unique key necessary to re-generate the same hash during future authentication attempts.
Step 5: User Verification
Retrieve the stored salt from the database, combine it with the password provided during login, and run the combination through the same hashing algorithm. If the newly generated hash matches the salted hash stored in the database, the user is verified.
Salting improves password security by adding unique, random data to each password before it is hashed, which prevents attackers from using precomputed tables or identifying identical credentials within a leaked database. This technique enhances protection by defeating rainbow table attacks, forcing unique hashes for duplicate passwords, increasing the computational cost for hackers, and mitigating dictionary and brute force attacks.
Prevents Rainbow Table Attacks
Rainbow tables are massive, precomputed databases of hashes for millions of common passwords used to reverse-engineer stolen data instantly. Salting makes these tables ineffective because an attacker would need to generate a new, unique rainbow table for every specific salt used in the database, which is computationally impossible.
Mitigates Dictionary and Brute Force Attacks
By appending a random string to the user's input, salting ensures that even common dictionary words do not match their standard hashed equivalents. This protects users with weaker passwords by ensuring their credentials do not appear as "low-hanging fruit" during automated dictionary or brute-force attempts.
Protects Duplicate Passwords
Identical passwords result in identical hashes, allowing attackers to immediately identify every user who shares a common password like "123456." Salting ensures that if two users share the same password, their stored hashes are completely different, preventing a single cracked password from compromising multiple accounts.
Increase Computational Cost
Salting removes the ability for hackers to attack an entire database in bulk. Instead of running a single attack against all stored credentials, attackers are forced to brute-force each account individually, exponentially increasing the time, processing power, and financial resources required to crack the data.
Password salting best practices require generating a unique, cryptographically secure random salt for every user that is at least 16 bytes long and stored alongside the hashed password. Effective implementation includes using unique per-user salts, ensuring sufficient salt length, utilizing modern hashing algorithms, practicing proper storage, avoiding predictable values, and implementing password peppering for defense-in-depth.
Unique Per-User Salt
Every account must have its own unique salt generated during registration or password changes. Never use a "site-wide" or "static" salt, as this allows attackers to use precomputed tables against your entire database. Unique salts ensure that even if two users choose the same password, their stored hashes will be completely different.
Sufficient Length
A salt must be long enough to ensure high entropy and prevent brute-force attacks against the salt itself. Industry standards recommend a minimum length of 16 bytes (128 bits), generally matching the output size of the hashing function used.
Modern Hashing Algorithms
Salting is most effective when paired with modern, slow, and memory-hard hashing algorithms like Argon2id (recommended), bcrypt, or scrypt. These algorithms are designed to resist high-speed cracking attempts from GPUs and ASICs, whereas fast hashes like MD5 or SHA-256 are no longer adequate for password storage.
Proper Storage
Store the salt in plain text in the same database table and row as the password hash. Salts do not need to be kept secret, their security value comes from being unique and random. Storing them with the hash ensures they are easily retrieved by the application during the login verification process.
Avoid Predictable Values
Never use usernames, email addresses, or other static user data as salts, as these are easily guessable by attackers. Always use a Cryptographically Secure Pseudo-Random Number Generator (CSPRNG) to create salts, ensuring they are truly random and unpredictable.
Password Peppering
For an additional layer of security, implement a password pepper, which is a secret key stored separately from the database (e.g., in a secure vault or environment variable). Unlike a salt, the pepper is not stored with the hash. If the database is compromised, the pepper provides a final line of defense because the attacker lacks the secret value required to verify the hashes.