Add secret sharing benchmarks and tests

The sanity checks ensure that, for a wide range of threshold values, a
quorum or superset can be recombined, but the secret is not recovered
from too few shares nor from a quorum with a corrupted share.

The known reconstructions were generated from random shares with this
implementation, but they guard against unintended representation changes
that would prevent old key shares being successfully recombined with
later versions of Pocketcrypt.

Author: arachsys

Makefile

@@ -11,9 +11,10 @@ override CFLAGS += -I.
 test: $(basename $(wildcard test/*.c))
 	@echo $(foreach TEST,$^,&& $(TEST))
 
-test/x25519-known test/x25519-sanity test/x25519-speed: x25519.[ch]
 test/duplex-known test/duplex-sanity test/duplex-speed: duplex.h
 test/gimli-known test/gimli-sanity test/gimli-speed: duplex.h
+test/shamir-known test/shamir-sanity test/shamir-speed: shamir.[ch]
+test/x25519-known test/x25519-sanity test/x25519-speed: x25519.[ch]
 
 tools: $(basename $(wildcard tools/*.c))