Creating collisions vs block

[t1mm3h]

Bitcoin.it claims it would take an attacker 2^107 more time to create a collision than a valid block. How is this number calculated? It must be a ratio between number of tries for a collision and number of tries for a valid block is created. 

[tysat]

If you were to intentionally try to make a collision, it would currently take 2^107 times longer to generate a colliding Bitcoin address than to generate a block. As long as the signing and hashing algorithms remain cryptographically strong, it will likely always be more profitable to collect generations and transaction fees than to try to create collisions.

Is that what you're talking about?

[Gabi]

Yup. The numbers of tries for a valid block to be created depend on the Difficulty. The tries for a collision depend on the bits of the hashing algorithm, 160, since for addresses RIPEMD-160 is used

[t1mm3h]

Is there a way to see how many addresses there are in existence today? (or an approximation)

[indee7]

Is there a way to see how many addresses there are in existence today? (or an approximation)

You can see them here: http://blockchain.info/charts/n-unique-addresses

[t1mm3h]

Is there a way to see how many addresses there are in existence today? (or an approximation)

You can see them here: http://blockchain.info/charts/n-unique-addresses

That shows how many unique addresses are used each day. Not how many there are in existence (or "seen"  on the network) in total. Is there another source?