If you’re an IT professional like me who likes to stay in touch with and expand your network, you’re probably familiar with LinkedIn (LNKD), operator of the world’s largest Internet-based professional network with 161 million members spanning over 200 countries and territories. In early June, the company learned that the encrypted passwords of over 6.4 million subscribers had been compromised and posted online.
In response to this incident, LinkedIn Director, Vicente Silveira, in a blog, said, “To the best of our knowledge, no email logins associated with the passwords have been published, nor have we received any verified reports of unauthorized access to any member’s account as a result of this event.” The company disabled passwords of those members believed to be at risk and sent them a message explaining how to reset their passwords. LinkedIn also stated that since the incident, it had enhanced its security measures (beyond SHA-1) by applying an additional layer of data protection know as “salting” to better secure members’ information.
Here’s how salting works. Before generating the hash (note: hash function is the transformation of a string of characters into a usually shorter fixed-length value or key that represents the original string) for each user password, you would create a random string of characters of a predetermined length and prepend this string to each plain text password. As long as the string (aka. a "salt") is of sufficient length and sufficiently random, the resulting hash will almost certainly be different each time the hash function is executed. By randomizing the hashes, lookup tables, reverse lookup tables, and rainbow tables become ineffective. Because an attacker won't know in advance what the salt will be, he or she can’t pre-compute a lookup table or rainbow table to crack passwords. If each user's password is hashed with a different salt, the reverse lookup table attack won't work either. Furthermore, in case an attacker tries to use brute force cracking in order to obtain passwords, Mykonos Web Security may be used to help prevent that.
On the other hand, if a legitimate user is logging into the Web site, because the user’s password associated salt is stored in the user database along with the hashed password, the authentication server will take the user supplied password and apply the user’s salt to obtain the hashed password. If there is a match, the user will successfully be authenticated.
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