In general, however, you should use the CFNetwork API for secure networking and the Certificate, Key, and Trust Services API for cryptographic services. Alternatively, in OS X, you can use the Secure Transport API.
Here is a link to the documentation for the Certificate, Key, and Trust Services API.
https://developer.apple.com/library/ios/documentation/security/conceptual/CertKeyTrustProgGuide/01introduction/introduction.html
Here is a link to the documentation for the Certificate, Key, and Trust Services API.
https://developer.apple.com/library/ios/documentation/security/conceptual/CertKeyTrustProgGuide/01introduction/introduction.html