# How is the block size of a block cipher related to how susceptible the block cipher is to a birthday attack?

For example what can you say about how susceptible Triple-DES is to a birthday attack due to the fact that it has a block size of 64-bits.

For example, say you'd use a 64 bit block cipher for CTR (counter) mode encryption and you'd use 32 bit for a random nonce and 32 bits for the counter. The counter will simply repeat after $2^{32}$ block encrypts. The random nonce however is succeptible to the birthday problem. This means that you'd have a relatively high chance of a collision (with one of the earlier values) after generating only a few nonces.