I have a number of different systems sending me email addresses, but I don't actually need the underlying email, just a hash of the email address. I know I can compare hash values to find matches across the senders, which is all I want to do, but what if each sending system uses a different salt or hash method. Is there some way to compare the resulting hash values I have?
Eg. Sender 1 sends me emails using sha1 and no salt. Sender 2 sends me email addresses using md5 and a salt (which they also send)
Can I take md5(sha1) and sha1(md5) and compare that hash output? Or do I need to specify that all emails should be hashed using the same method? Is there a better way that will allow each sender to select the hash method they want to use but still allow me to compare email addresses across senders?