just-launch | Launch any browser , on any OS , with a fresh session | File Utils library
kandi X-RAY | just-launch Summary
kandi X-RAY | just-launch Summary
Launch any browser, on any OS, with a fresh session!
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Currently covering the most popular Java, JavaScript and Python libraries. See a Sample of just-launch
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QUESTION
I was reading a post in Troy Hunt's blog (https://www.troyhunt.com/ive-just-launched-pwned-passwords-version-2/), about a feature called "Pwned Passwords" that checks if your password is in a database with more than 1 billion leaked passwords.
To do this check without passing your password, the client code hash it and pass just the first five chars of this hash, the backend returns all the sha1 hashes of the passwords that starts with the prefix that you passed. Then, to check if the hash of your password is in the database or not, the comparison is made on client code.
And he put some info about the data of these hashed passwords...
- Every hash prefix from 00000 to FFFFF is populated with data (16^5 combinations)
- The average number of hashes returned is 478
- The smallest is 381 (hash prefixes "E0812" and "E613D")
- The largest is 584 (hash prefixes "00000" and "4A4E8")
In the comments, people was wondering if the presence of this "00000" is a coincidence or is math...
Could someone that understands the SHA1 algorithm explain it to us?
...ANSWER
Answered 2018-Feb-25 at 06:36It's either a coincidence, or (less likely) an artifact/error in acquiring or assembling the results for publication.
Not that it looks like a significant outlier. The spread that's described (381 min, 478 average, 584 max) seems like an even spread for the sample size. A graph of the entire corpus would probably look pretty random.
Like any reasonably constructed hashing algorithm, character frequency in SHA1 results should be randomly distributed. (If SHA1 had some kind of bias, this would be major news in the math and cryptography/cryptology community!)
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