# Number codes

1. Jun 28, 2007

### debayan

how are the secret codes for recharging the credit of a phone or the secret credit card numbers gnerated? i hrd something with prime nos. any way to decode them??????

2. Jun 28, 2007

### HallsofIvy

I assume you are talking about "trap door" codes- where you can be told how to encode a messsage but that doesn't help you decode it. I don't know all the details but essentially it uses the fact that while it is relatively easy to multiply two large (prime) numbers together, it is almost impossible to factor the product without knowing the two factors to begin with. Yes, it is possible to decode them:
(1) Know the correct factors to begin with
(2) Use very, very powerful computer for a very, very long time.

3. Jun 28, 2007

### CompuChip

Well, it can be cracked, but there's no smooth way to do it.
If there were, http://www.rsa.com/rsalabs/node.asp?id=2092 [Broken] wouldn't give out $30,000 to the one who factors a number of "just" 212 decimal digits (and$200,000 for a 600+ digit number) :)

Last edited by a moderator: May 2, 2017
4. Jun 28, 2007

### Feldoh

Remember what HallsofIvy was just saying XD