Obscure / encrypt an order number as another number: symmetrical, “random” appearance?

Question

Client has an simple increasing order number (1, 2, 3...). He wants end-users to receive an 8- or 9- digit (digits only -- no characters) \"random\" number. Obviously, this

Answer 1

In 9 digit number, the first digit is a random index between 0 and 7 (or 1-8). Put another random digit at that position. The rest is the "real order number:

• Orig order: 100
• Random index: 5
• Random digit: 4 (guaranteed, rolled a dice :) )

• Result: 500040100

• Orig Nr: 101

• Random index: 2
• Random digit 6
• Result: 200001061

You can decide that the 5th (or any other) digit is the index.

Or, if you can live with real order numbers of 6 digits, then you can introduce "secondary" index as well. And you can reverse the order of the digits in the "real" order nr.