Hash Range Queries

Transcript

1. Hash Range Queries For simple, privacy-preserving data-sharing

2. https://blog.cloudflare.com/validating-leaked-passwords-with-k-anonymity/
 https://www.troyhunt.com/ive-just-launched-pwned-passwords-version-2/ Not my original idea

3. https://api.pwnedpasswords.com/pwnedpassword/password A request for a single password reveals who is

   interested in this password. Maybe not that interesting for a widely-used value …

4. https://api.pwnedpasswords.com/pwnedpassword/p1nkyp13 But how many people would use their favorite my

   little pony character with vowels replaced with numbers?

5. Do you trust the person operating the service? • Are

   they doing something else with the data? • Are they securing the data?
6. None

7. How can a client get a single record from a

   server without revealing the record identifier to the server?

8. The Easiest Way: Hashed Identifiers

9. None
10. None

11. But rainbow tables exist

12. None

13. The Hard Way: Private Set Intersection

14. None
15. None

16. The Middle Way: k-Anonymity

17. https://en.wikipedia.org/wiki/K-anonymity Every record is unique

18. https://en.wikipedia.org/wiki/K-anonymity k-Anonymity: 2 for any combination of Age + Gender

    + State found in any row of the table there are always at least 2 rows with those exact attributes Suppression Suppression Generalization

19. https://blog.cloudflare.com/validating-leaked-passwords-with-k-anonymity/ By using this property, we are able to seperate

    hashes into anonymized "buckets".

20. https://blog.cloudflare.com/validating-leaked-passwords-with-k-anonymity/ A client is able to anonymize the user-supplied hash

    …

21. https://blog.cloudflare.com/validating-leaked-passwords-with-k-anonymity/ … and then download all hashes in the same

    anonymized "bucket" as that hash … {

22. https://blog.cloudflare.com/validating-leaked-passwords-with-k-anonymity/ { 5baa61e4c9b93f3f0682250b6cf8331b7ee68fd8 5baa61f4c0b12f0a6691121c7de9420c8ff12c1f 5baa61aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa 5baa61bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb 5baa61cccccccccccccccccccccccccccccccccc 5baa61e4c9b93f3f0682250b6cf8331b7ee68fd8 5baa61f4c0b12f0a6691121c7de9420c8ff12c1f 5baa61aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa

    5baa61bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb 5baa61cccccccccccccccccccccccccccccccccc … then do an offline check to see if the user- supplied hash is in that breached bucket.