Do all Monero addresses start with 4?
I'm not sure, it might be a hardcoded default.
I'm not sure why florida.haunted is being a jerk either...
Better question would be "why are XMR addresses some 3-5 times longer than BTC ones". For example, I don't know why. It would be nice, if somewhat short-alias system being applied to XMR addresses... But it is still very very tiny wish to devs.
Because they are basically what u know as stealth addresses from Bitcoin. Having one long address that you reuse the whole time is definately easier to deal with than having changing addresses for every transaction.
“The destination of each CryptoNote output (by default) is a public key, derived from recipient’s address and sender’s random data. The main advantage against Bitcoin is that every destination key is unique by default (unless the sender uses the same data for each of his transactions to the same recipient). Hence, there is no such issue as “address reuse” by design and no observer can determine if any transactions were sent to a specific address or link two addresses together.
First, the sender performs a Diffie-Hellman exchange to get a shared secret from his data and half of the recipient’s address. Then he computes a one-time destination key, using the shared secret and the second half of the address. Two different ec-keys are required from the recipient for these two steps, so a standard CryptoNote address is nearly twice as large as a Bitcoin wallet address. The receiver also performs a Diffie-Hellman exchange to recover the corresponding secret key.”
An alias system is tricky, it opens up a lot of abuse cases, for example people can just register an alias for the various exchanges and trick people into sending coins there. As noone can control the aliases it will end in chaos i supose, at least the currently available alias systems are far from perfect...
