xmlsec

https://www.aleksey.com/xmlsec/index.html

XML Security Library is a C library based on LibXML2. The library supports major XML security standards:

Slackbuild

   1 wget https://slackbuilds.org/slackbuilds/14.2/libraries/xmlsec.tar.gz
   2 tar xvzf xmlsec.tar.gz 
   3 cd xmlsec
   4 wget https://www.aleksey.com/xmlsec/download/xmlsec1-1.2.29.tar.gz
   5 ./xmlsec.SlackBuild 
   6 installpkg  /tmp/xmlsec-1.2.29-i586-1_SBo.tgz