I present to you: "DSi Encryption Put In Perspective", also known as "I Love Crushing People's Dreams".
The DSi uses 128-bit encryption (IIRC).
How do you break it? You find the correct encryption key.
How many encryption keys are there? 2 (binary, a bit) to the 128th power (number of bits), divided by 8 (8 bits in a byte).
That's so many that the calculator that comes with windows (at least XP) can't even display the number without reverting to scientific notation.
128-bits is...
340,282,366,920,938,463,463,374,607,431,768,211,456 possible values in binary.
However, Since there's 8 bits in a byte, you divide 128 by 8 and get 16. That's 16 bytes, 16 characters.
That's 18,446,744,073,709,552,000 possible values, ranging from 0x0000000000000000 to 0xFFFFFFFFFFFFFFFF. Eighteen quintillion possible keys.
The actual number is a bit less less since a key will be a certain number of digits and be designed to not have repeating segments, but this puts it in perspective.
Let's say that you have a computer program which can try 50,000 unique keys a second.
That's 3,000,000 keys a minute.
180,000,000 keys in an hour.
4,320,000,000 keys a day.
1,576,800,000,000 keys in one year.
It would take 11,698,848 years to try all the keys at that speed.