logjam: daily C challenge, 26 October 2026

Your mission

Return the smallest key size on the server's list.

today's brief

May 2015. Logjam showed that a server still carrying 1990s export grade Diffie-Hellman could be talked down to a 512 bit group by anyone sitting in the middle. Those ciphers existed because of a US export rule that had been dead since 2000. Nobody swept them off the menu. A server is only as strong as the weakest thing it will still agree to.

See it in action

weakest({2048,1024,512}, 3): 512
weakest({2048,2048}, 2): 2048
weakest({}, 0): -1

Your checklist

sizes holds n key sizes in bits, each one at least 1.
Return the smallest size on the list.
Return -1 when the list is empty.

Constraints

Expected file: logjam.c
Allowed functions: None. Write every helper yourself.