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8 comments on “How Can a Hacker Try All Possible Passwords If Systems Block Failed Login Attempts?”

  1. Leo,
    This is unrelated to the above excellent article, I also use 1Password and find it indispensable.
    But, here is my plea for help:
    Couple years ago I updated Microsoft Office and somehow the update caused two mailboxes of the same name to be created. Email randomly comes to both, never the same email to both however, without obvious reason. How do I safely eliminate one of these mailboxes please?

  2. I’m curious. If a password, such as “Fido”, creates the hash “5baa61e4c9b93f”, and the password is changed to “Fidodog”, does the first part of the original hash for “Fido” change appreciably?

    Sometimes when I log into a website, the service will see I’m using a different computer and ask for additional verification, like my first car (the correct answer for me would be “spaghetti”). Kudos to those companies. If I was using a different computer (or perhaps a hacker on their computer), I only wish they would ask for additional verification whether the password was right or wrong. If the password or additional information was incorrect, respond with “either the password was incorrect or the additional information was incorrect”. A hacker would have two problems to solve.

    • If a password changes in even the smallest way (Fido -> fido, which is a one-bit change), the new hash will be COMPLETELY different. That’s one of the characteristics of a good hash algorithm: a small change on input results in a massive change on output.
      sha1 hash of “Fido”: c6eab3324f4657a4c4c751fa472155eef159a4c8
      sha1 hash of “fido”: cc22a138b5b04eb06600eabb1a1cd19ccf50e930

    • Adding even one letter or even one bit to a password would not only change the first par to the hash, it would change the hash completely indistinguishable from the original. The hash is a result of a complex cryptographic mathematical calculation.
      Here is an example of a hash of fido using the SHA3-224 hash
      and here is a hash of fido1

      If you want to play with it here’s a website that calculates hashes,

  3. I must be missing something. In order for a hacker to be able to make use of an exposed hash database, he must be able to apply the same hashing algorithm used by the legitimate owner of that database. It would seem that the number of potential hashing algorithms would explode the required trials geometrically. Do hackers also use a database of potential hash algorithms that are well established?

    • Basically, yes. It’s quite possible for security, when done properly, to make attacking the database of hashes impractical as well. (A little salt can often ruin the entire effort.) Unfortunately two things: 1) “done properly” isn’t always, and 2) often the same breach that allowed the hacker to exfiltrate the database may also have given them access to the code implementing the hashing algorithm.

  4. Even though you recommend never using the same password for different sites I do it often for sites that I don’t care much if someone logs onto my account. For example, I use the same eight-character upper & lower case letters plus special characters password for Consumer Reports as I do for CVS Pharmacy and several other sites. My reasoning is that I can’t think of anything a hacker could do on these sites that would be extremely harmful to me. First question: Am I being naive about this and exposing myself to harm?

    And I let my Firefox browser memorize the password for those sites but not for others that I consider more sensitive, such as my bank. Second question: Am I being too paranoid about the safety or lack thereof for browser-memorized passwords?


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