IOS Security framework p12 and expeiration date - ios

Question

I'm trying to extract expiration date from p12 data.
I read apple documentation from start to end and wasn't able to find out how to do it -
https://developer.apple.com/library/prerelease/mac/documentation/Security/Conceptual/CertKeyTrustProgGuide/CertKeyTrustProgGuide.pdf
my code as in the pdf, i'm loading a SecKeyRef using NSData with private key p12 data and am able to decrypt data which was encrypted on the server.
The thing is i'm trying to prevent the decryption from taking place when a p12 is expired but i can not detect when the key is expired.
On java the solution was very simple
private PrivateKey decodeP12Key(String key) throws KeyStoreException, CertificateException, NoSuchAlgorithmException, IOException, UnrecoverableKeyException,InvalidKeyException {
KeyStore kStore = KeyStore.getInstance(KeyType.P12.getKeyValue());
String[] words = key.split(" ");
return null;
}
X509Certificate cert = (X509Certificate)kStore.getCertificate(alias);
if(isExpired(cert)){
throw new InvalidKeyException("Invalid key used, please check if your key is valid and not expired");
}
PrivateKey pKey = (PrivateKey)kStore.getKey(alias,"".toCharArray());
return pKey;
cipher.init(Cipher.DECRYPT_MODE, key);
return cipher;
}
private boolean isExpired(X509Certificate cert){
Date expirationDate = cert.getNotAfter();
Date beginDate = cert.getNotBefore();
Date currentDate = new Date(System.currentTimeMillis());
return currentDate.after(expirationDate) || currentDate.before(beginDate);
}
Anyone know how to do the same on ios ?
EDIT:
attach also the question on apple forums
https://forums.developer.apple.com/message/53696#53696
Thanks