What does a birthday attack tell you? Select one answer that is most appropriate. Partial credits may be given.

a$.$

Using a birthday attack, the collision resistance of a cryptographic hash function with n$-$bit output, no matter how strong it is$,$ is $2$n$/2$ rather than $2$n$.$

b$.$

Birthday attacks do not apply to hash functions.

c$.$

Birthday attacks tell us the following: When generating uniformly at random a sequence of n$-$bit strings, one is likely to see at least an n$-$bit string the second time after about n$1/2$ strings are generated.

d$.$

Both a and b$.$

e$.$

Both a and c$.$

f$.$

Both b and c$.$

g$.$

All of the above.

h$.$

None of the above.