WEBVTT

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The rainbow tables are fast and effective at cracking passwords because each password is hashed the

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same way. Hashes are in fact one way functions.

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For example if a hacker has a rainbow table with the hash of the password spatial player any user

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that has the same password will have the same hash and his password will be cracked as well.

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Since most people use common passwords or reused passwords it makes cracking an easy process. To solve

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this issue

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a salt is used.

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You can see here at the crackstation.net that it can crack only non salted hashes. Let's see what

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the salt. Instead of computing and saving the hash of the password

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the operating system will compute and save the hash of the password together with a salt.

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The salt is a randomly generated string for each password. The salt is not secret just the password is. 

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Let's take a look at the file that contains the hashes of the user's passwords in Linux. That's

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the shadow file from etc directory.

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This is an entry for a user and a password.

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This is the user, the number 6 is a code for the hash

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algorithm used, 6 means sha512, and then comes the salt.

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This is the salt, until the dollar sign. And then comes the hash of the password and the salt, until the

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colon sign, 

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until this point. The salt is randomly generated for each password but it is not secret like the

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password is.

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It is combined with the password and added to the hashing process to force the uniqueness of the output

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hash.

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In other words the same password will give different hashes because of this random salt.

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This mitigate passwords attacks like rainbow tables. If a hacker has found the clear text password from

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the hash all other passwords that part of the same are still secure because their hash is different.

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I've shown you a real example of two users that have the same password, but different hashes, in a previous

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lecture where I've also explained in detail how Linux system stores

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the passwords. In fact these are the users, user 1 and user to have the same password but 

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different hashes saved in the shadow file.

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The hash is unique because the salt is unique.

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I'd recommend you to watch that video again if you feel the need. Thank you.

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That's all!