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Salting passwords

From: PHP with MySQL Essential Training

Video: Salting passwords

In this movie, we're going to learn about another important concept in encryption and in password security, which is the concept of salt. Before we talk about salt, we first need to talk about rainbow tables, because that's the main reason that we need salt. Now imagine that a hacker gets a hold of our database. But we've been smart and we encrypted our database. Let's say we encrypted it using the SHA-1 algorithm. So, those are now all encrypted and you can not tell what the plain text password was. but the hacker could take one of those values and then have a little program that just runs and tries every single value possible.

Salting passwords

In this movie, we're going to learn about another important concept in encryption and in password security, which is the concept of salt. Before we talk about salt, we first need to talk about rainbow tables, because that's the main reason that we need salt. Now imagine that a hacker gets a hold of our database. But we've been smart and we encrypted our database. Let's say we encrypted it using the SHA-1 algorithm. So, those are now all encrypted and you can not tell what the plain text password was. but the hacker could take one of those values and then have a little program that just runs and tries every single value possible.

Every word in the dictionary, every combination of letters and numbers, tries everything possible. Looking for a result of the SHA1 hashing algorithm that matches your result. And if he can generate a result that matches, then he will know what the input was. He'll know what the original password was. So, you may be thinking, well that's going to take a long time, right? I mean, to try every single word, every single password. Computers are fast, but that's still going to take a very long time. but what if we pre-compute those values? What if we go ahead and try every combination and store the result of that in a database or in a table so that we can look it up? So, for example, if our password is secret, encrypted with SHA-1, and then the result that we store in our database is e5e9fa1b, and so on. Well, if the hacker, ahead of time, has created these rainbow tables, he will have tried secret, passed it into the SHA-1 hash, and will have gotten the same result.

So, look at our database, and he'll see, e5e9fa1. Let me look that up in my rainbow tables. that corresponds to secret. And voila, just like that, he can use these pre-computed tables to immediately know what the password is. That's the reason why we use salt. Salt is going to add additional data to the password before encryption. So, for example, a very simple salt would be to do something like this. Put salt on the {$password}. So, now it's not just the password anymore, it has some other string with it as well.

Now in order to know the password you do also have to know the salt string. A rainbow table still could be generated that had the string, put salt on the something. But even if you got that. Even if you figured out what that was. You wouldn't necessarily know what the password was. So, rainbow tables could be used, but they would be almost impossibly large. But we don't have to stop there. We can go even further. We can also create our Salt by using strings unique to each user. And that way, just because you figure out the salt or the password for one user, you haven't necessarily compromised another user, because theirs is different.

A very simple example of this would just be to use their username. Now, that's not a great candidate really, because username is probably also stored in the database. But still it would be something that would be varied in our salt and would give us a different result. So now knowing the password requires knowing the salt string and knowing that user string and also knowing how it's used in the salt as well. So, rainbow tables are still impossibly large but each user's salt is unique too. So, even if you're able to crack on user you'd still have to start all over again for another user. And we can go even further by having random salt. That is we can create our salt by using pseudo-random strings, not by using something that's predictable like the user name. So, we have mt_rand or time.

Those are PHP functions that return things that are pseudo-random, they're not 100% random but pretty close. And then we can generate our string like, put salt on the {$password} at, and then we can have the time appended to it. And that would then give us a different result. So, now knowing the password is going to require knowing what the random string is. Rainbow tables become completely useless, as each user's hash is almost random, almost unique. Now there's one problem with this which is that now we've generated this fantastic salt.

But we need to be able to reuse that salt in the future. Right? We need to have it available for our purposes so when a user comes back to the site and wants to log in, we can apply that same salt to the password. To be able to regenerate the hash that matches what's in the database. So, we'll need to store our salt in the database. So when using user data for salt. And user data could change. Or when using random salt. We store the salt in the database. Not the password, just the salt by itself. Just so that we have it available to us. It's also a good practice to hash the salt, so that it also will not be in plain text.

Just so that there's no way that it gives away anything about where it came from, or how it was generated. Now, if all that seems kind of complicated, let me walk you through the actual PHP steps that we're going to use to do it. This is sort of a simple version of what we're going to create. We're going to generate our salt, and our salt is going to use mt_random to generate a random string. And then we'll pass that into unique id, which is the function that will generate a unique id, and make sure that it's unique. True helps make sure that it's extra secure, and we'll take that whole thing and we'll hash it using the MD5 algorithm so that it's encrypted and not in plain text.

And we can't tell where it came from originally. So that's how we'll get our salt. And then, we'll take our salt and we'll append it to a format string. We'll take the two together, format in salt and that's what we'll pass into the crypt method, in the first example I showed you, I just called it salt. But the salt actually includes the format at the beginning, so it's debatable whether you actually call that format part the salt or not. I'm going to make it clearer by just saying it's the format and the salt and calling the salt just the string that goes after it. So, hopefully that explains to you the concept behind salt, why we need it, and how we're going to use it in our crypt function.

Let's try writing the code for the next movie.

Show transcript

This video is part of

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PHP with MySQL Essential Training

131 video lessons · 34280 viewers

Kevin Skoglund
Author

 
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  1. 4m 8s
    1. Welcome
      1m 0s
    2. Using the exercise files
      3m 8s
  2. 15m 6s
    1. What is PHP?
      3m 52s
    2. The history of PHP
      2m 51s
    3. Why choose PHP?
      4m 10s
    4. Installation overview
      4m 13s
  3. 54m 53s
    1. Overview
      2m 33s
    2. Working with Apache Web Server
      6m 56s
    3. Changing the document root
      7m 24s
    4. Enabling PHP
      6m 16s
    5. Upgrading PHP
      3m 30s
    6. Configuring PHP
      10m 3s
    7. Installing MySQL
      5m 46s
    8. Configuring MySQL
      7m 24s
    9. Text editor
      5m 1s
  4. 31m 25s
    1. Overview
      3m 27s
    2. Installing WampServer
      5m 46s
    3. Finding the document root
      2m 24s
    4. Configuring PHP
      8m 12s
    5. Configuring MySQL
      5m 45s
    6. Text editor
      5m 51s
  5. 19m 12s
    1. Embedding PHP code on a page
      6m 43s
    2. Outputting dynamic text
      5m 55s
    3. The operational trail
      2m 27s
    4. Inserting code comments
      4m 7s
  6. 1h 18m
    1. Variables
      7m 50s
    2. Strings
      4m 38s
    3. String functions
      8m 54s
    4. Numbers part one: Integers
      6m 27s
    5. Numbers part two: Floating points
      5m 25s
    6. Arrays
      10m 0s
    7. Associative arrays
      6m 37s
    8. Array functions
      6m 33s
    9. Booleans
      3m 50s
    10. NULL and empty
      5m 15s
    11. Type juggling and casting
      8m 27s
    12. Constants
      4m 43s
  7. 27m 37s
    1. If statements
      6m 0s
    2. Else and elseif statements
      4m 16s
    3. Logical operators
      7m 30s
    4. Switch statements
      9m 51s
  8. 42m 15s
    1. While loops
      8m 41s
    2. For loops
      5m 59s
    3. Foreach loops
      8m 16s
    4. Continue
      8m 28s
    5. Break
      4m 8s
    6. Understanding array pointers
      6m 43s
  9. 37m 25s
    1. Defining functions
      8m 25s
    2. Function arguments
      5m 32s
    3. Returning values from a function
      7m 33s
    4. Multiple return values
      4m 53s
    5. Scope and global variables
      6m 2s
    6. Setting default argument values
      5m 0s
  10. 20m 18s
    1. Common problems
      3m 47s
    2. Warnings and errors
      8m 36s
    3. Debugging and troubleshooting
      7m 55s
  11. 57m 57s
    1. Links and URLs
      5m 33s
    2. Using GET values
      5m 35s
    3. Encoding GET values
      8m 41s
    4. Encoding for HTML
      9m 26s
    5. Including and requiring files
      7m 40s
    6. Modifying headers
      6m 45s
    7. Page redirection
      6m 43s
    8. Output buffering
      7m 34s
  12. 1h 3m
    1. Building forms
      7m 28s
    2. Detecting form submissions
      5m 59s
    3. Single-page form processing
      7m 57s
    4. Validating form values
      10m 40s
    5. Problems with validation logic
      9m 54s
    6. Displaying validation errors
      7m 23s
    7. Custom validation functions
      6m 28s
    8. Single-page form with validations
      7m 25s
  13. 28m 5s
    1. Working with cookies
      2m 49s
    2. Setting cookie values
      5m 55s
    3. Reading cookie values
      6m 1s
    4. Unsetting cookie values
      4m 51s
    5. Working with sessions
      8m 29s
  14. 48m 39s
    1. MySQL introduction
      6m 43s
    2. Creating a database
      7m 41s
    3. Creating a database table
      7m 42s
    4. CRUD in MySQL
      5m 48s
    5. Populating a MySQL database
      7m 32s
    6. Relational database tables
      6m 40s
    7. Populating the relational table
      6m 33s
  15. 56m 4s
    1. Database APIs in PHP
      4m 51s
    2. Connecting to MySQL with PHP
      7m 45s
    3. Retrieving data from MySQL
      8m 47s
    4. Working with retrieved data
      6m 12s
    5. Creating records with PHP
      6m 58s
    6. Updating and deleting records with PHP
      9m 6s
    7. SQL injection
      3m 5s
    8. Escaping strings for MySQL
      6m 45s
    9. Introducing prepared statements
      2m 35s
  16. 35m 58s
    1. Blueprinting the application
      7m 19s
    2. Building the CMS database
      5m 14s
    3. Establishing your work area
      4m 38s
    4. Creating and styling the first page
      4m 22s
    5. Making page assets reusable
      6m 36s
    6. Connecting the application to the database
      7m 49s
  17. 32m 49s
    1. Adding pages to the navigation subjects
      5m 58s
    2. Refactoring the navigation
      6m 7s
    3. Selecting pages from the navigation
      6m 2s
    4. Highlighting the current page
      5m 26s
    5. Moving the navigation to a function
      9m 16s
  18. 1h 45m
    1. Finding a subject in the database
      9m 48s
    2. Refactoring the page selection
      10m 52s
    3. Creating a new subject form
      6m 55s
    4. Processing form values and adding subjects
      11m 20s
    5. Passing data in the session
      9m 16s
    6. Validating form values
      9m 40s
    7. Creating an edit subject form
      8m 30s
    8. Using single-page submission
      7m 44s
    9. Deleting a subject
      9m 44s
    10. Cleaning up
      10m 37s
    11. Assignment: Pages CRUD
      4m 30s
    12. Assignment results: Pages CRUD
      6m 10s
  19. 39m 26s
    1. The public appearance
      8m 52s
    2. Using a context for conditional code
      11m 37s
    3. Adding a default subject behavior
      6m 9s
    4. The public content area
      5m 51s
    5. Protecting page visibility
      6m 57s
  20. 1h 3m
    1. User authentication overview
      4m 3s
    2. Admin CRUD
      8m 41s
    3. Encrypting passwords
      7m 26s
    4. Salting passwords
      5m 42s
    5. Adding password encryption to CMS
      11m 54s
    6. New PHP password functions
      3m 13s
    7. Creating a login system
      11m 28s
    8. Checking for authorization
      5m 48s
    9. Creating a logout page
      5m 40s
  21. 2m 4s
    1. Next steps
      2m 4s

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