Hashes, salt, and pepper
Salt and Pepper
© Lead Image © topnat, 123RF.com
Cryptographic hash functions help you protect your passwords, but hashing is only secure if properly understood.
Hash functions are an integral part of computer science – and not just with databases and checksums. Hashes were originally intended for storing data efficiently in memory, but the hashing concept has evolved into a technique for securely storing passwords.
Linux writes the password hash values to the /etc/shadow file, which you can only read if you have root privileges. But even if you have the root password, you'll find it difficult to learn any useful access information. The function used to store the password hash values in etc/shadow is a one-way function, which means you can't work backward from the hash value to create the original password – at least in theory. As you'll learn in this article, attackers still sometimes manage to crack these supposedly irreversible hash functions.
What is a Hash?
The idea of a hash is simple: An address is calculated from the value that is to be stored. Suppose, for example, you need to store the four user names Fritz, Laempel, Max, and Moritz. A hash function would calculate a numeric value from these names.
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