Say you're negotiating a deal with an external party and to be able to move forward you need to know *how many customers do we have in common*? Neither party is at this stage interested in sending their list of customers.

My solution to this problem is by using the new MdFive function in SeoTools 5.0.

MD5 which stands for Message Digest algorithm 5 is a widely used cryptographic hash function that was invented by Ronald Rivest in 1991. The idea behind this algorithm is to take up a random data (text or binary) as an input and generate a fixed size “hash value” as the output. The input data can be of any size or length, but the output “hash value” size is always fixed.

(from https://www.gohacking.com/what-is-md5-hash/)

This is how to do it:

- Take all your user's emails (or what every sensitive data you want to compare) and put them in one column in Excel.
- Apply
`=MdFive()`

on each row (enter the formula in the first row and then double-click on the black square in the lower right corner of the cell to populate all the remaining rows). - Select all the generated Md5 values and copy. Press
`CTRL+ALT+V`

and*Paste as Values*. - Delete the column with the emails.
- The other party also does step 1-4 and you can now exchange files.
- Now we need to compare what Md5 values exists on both lists. There are several ways to do this, here's a suggestion:

This is a companion discussion topic for the original entry at https://seotoolsforexcel.com/securely-compare-customer-lists-from-two-parties/