Two things are required to get elog (tested with 2.8.1) to compile on OpenBSD (tested on OpenBSD 4.8):

Step 1 - Patch Makefile:

--- Makefile~ Mon Jan 24 21:38:09 2011
+++ Makefile Mon Jan 24 21:42:57 2011
@@ -50,6 +50,10 @@
 RM = /usr/bin/rm -f
 endif

+ifeq ($(OSTYPE),OpenBSD)
+LIBS += -lcrypto
+endif
+
 ifeq ($(OSTYPE),Darwin)
 OSTYPE=darwin
 endif

Step 2 - Use "gmake" instead of the standard "make" to build.