Sagar Shah wrote: > which libraries does des_ecb_encrypt() uses, try to link with that > libraries. try out > > gcc -o $optname $programname.c -l$libname It'll be OpenSSL's libeay.a or libeay.so, i.e. you want to add '-leay' to your link line plus '-L<path to libeay.*>' if necessary. Good luck, Rup.