You don't need the SHA1 or anything within the blobs even. Just an IP address & user-agent pair is enough to uniquely identify a user with some accuracy, and th

You don't need the SHA1 or anything within the blobs even. Just an IP address & user-agent pair is enough to uniquely identify a user with some accuracy, and that accuracy only goes up the more data you add. It'll never be 100% accurate, but for ad targeting, it doesn't need to be - a "hunch" is more than enough since getting it wrong leaves you no worse than you were before.