各位高手请帮帮忙，这是什么问题，多谢了！！
今天在redhat4.7环境下部署vsftpd-2.0.7，把 #undef VSF_BUILD_SSL改成 #define VSF_BUILD_SSL，make的时候就出现了以下错误：
ssl.c: In function 'ssl_cert_digest':
ssl.c:549: warning: implicit declaration of function 'EVP_sha256'
ssl.c:550: warning: passing arg 2 of 'X509_digest' makes pointer from interger without a cast
ssl.o(.text+0x638): In function 'ssl_cert_digest':
: undefined reference to 'EVP_sha256'
collect2: ld returned 1 exit status
make: *** [vsftpd] Error 1
请各位支支招，到底是什么问题，多谢了！！
