PHP：致命错误：调用未定义的函数openssl_pkcs12_read（）

I'm using PHP to read encryted file using opensll.

when doing

openssl_pkcs12_read($storedfile, $certificateinfo, $passwd)

in my script, error came out is :

Fatal error: Call to undefined function openssl_pkcs12_read()

I'm trying to install openssl extension for my Suse Linux Enterprise Server 11.

Can anybody help me how to install openssl extension in SLES. or how to solve this problem.

thanks