Understanding Have I Been Pwned’s Use of SHA-1 and k-Anonymity

From troyhunt.com

Understanding Have I Been Pwned's Use of SHA-1 and k-Anonymity

Four and a half years ago now, I rolled out version 2 of HIBP’s Pwned Passwords that implemented a really cool k-anonymity model courtesy of the brains at Cloudflare. Later in 2018, I did the same thing with the email address search feature used by Mozilla, 1Password and a handful of other paying subscribers. It works beautifully; it’s ridiculously fast, efficient and above all, anonymous. Yet from time to time, I get messages along the lines of this:

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