3 ms·
The difference is "for a given message M1". In the 2nd requirement, you may choose both M1 and M2. For the 1st requirement, you are given M1 and must find M2.
by coldpie 11mo ago
The difference is "for a given message M1". In the 2nd requirement, you may choose both M1 and M2. For the 1st requirement, you are given M1 and must find M2.