What technique involves appending a unique string of characters to password hashes for added security?

Salting is a technique used to enhance the security of password hashes by adding a unique string of characters, known as a salt, to each password before it is hashed. This process ensures that even if two users have the same password, their hashed values will be different due to the unique salt.

The primary benefit of salting is to defend against pre-computed attacks, such as rainbow table attacks, where an attacker uses pre-calculated hash tables of common passwords to quickly crack hashed passwords. By incorporating a salt, the resulting hash value becomes unique to each password-salt combination, requiring the attacker to compute hash values for each user individually, which is significantly more time-consuming and resource-intensive.

In contrast, hashing alone simply converts data (like a password) into a fixed-length string of characters, but does not provide any added protection against common attack strategies without the inclusion of a salt. Encryption transforms data into a secure format but does not inherently protect password integrity like salting does. Tokenization, on the other hand, replaces sensitive data with non-sensitive equivalents but serves a different purpose than that of strengthening password security. Thus, salting is the correct method for adding a unique string to password hashes for enhanced security.