squirrelmail should be ported to use NSS library for cryptography. See the tracking bug for details and links on how it could be done.
Standard SquirrelMail package uses only own one time pad functions. Other crypto functions are provided by PHP. PHP does not provide NSS functions. Link PHP OpenSSL extension to NSS and SquirrelMail will use NSS. Not a SquirrelMail bug. All your links are about porting C apps and none talks about porting PHP scripts.
Should this bug be closed based on the information in comment #1?