So I was trying to compile a code which has a SHA1 function .. I included following header: #include <openssl/sha.h> And I got the following error while compiling: test.c:9:5: error: 'SHA1' is deprecated: first deprecated in OS X 10.7 [-Werror,-Wdeprecated-declarations] SHA1(msg, strlen(msg), hs); ^ But man pages still have the descriptions for that function. Can anyone suggest any other header for a similar function ( MD5 or SHA1 )? PS - also do I need to link any libraries while compiling using gcc?