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

Pick a 8 or 9 digit number at random, say 839712541. Then, take your order number's binary representation (for this example, I'm not using 2's complement), pad it out to the same number of bits (30), reverse it, and xor the flipped order number and the magic number. For example:

1         = 000000000000000000000000000001

Flip      = 100000000000000000000000000000
839712541 = 110010000011001111111100011101
XOR       = 010010000011001111111100011101 = 302841629

2         = 000000000000000000000000000010

Flip      = 010000000000000000000000000000
839712541 = 110010000011001111111100011101
XOR       = 100010000011001111111100011101 = 571277085

To get the order numbers back, xor the output number with your magic number, convert to a bit string, and reverse.