String encryption - suggestions asked

[jacek]

If i were to use one of say, 100 schemes, i only have 100 possible combinations. Compare this to using a key of just 8 bits that gives you 256 possible combinations. You get greater security with less work since you don't need to create a bunch of different scrambling methods.

What about 20922789888000 schemes? And all you need is to write a single method that permutes 16-bit value. As long as the server can't tell the difference between a valid string and scrambled one (either by using data it has at hand or by asking one of the clients), you're protected by plain probability.

I believe using a strong method of encryption along with a stable framework for key distribution would be the wise choice, in the field.

Yes, you're right, but it's hard to meet those same-length and digits-only requirements.