Asymmetric Encryption macOS

I have a homework in which I need to create an App that encrypts and decrypts some text. It's nothing too fancy, but I do need to use both symetric and asymmetric encryption (for key sharing). I can't find how to do either of them. First I tried to do asymmetric using the Certificate, Key, and Trust Services API, but found that

SecKeyEncrypt

and

SecKeyDecrypt

are not available in OS X.

I tried with the Security Tranforms API, but its documentation says it works only with symmetric encryption. Yet in this other question the person who answered states that it is possible to use asymetric encryption, so I thought I should just pass an RSA key to a

SecKeyEncryptTransform

but that didn't work.

Also according to a WWDC session they have unified SecKey it across iOS and macOS APIs, I thought that means you can now use

SecKeyEncrypt

in macOS but it is not the case, so first I should ask what is the unification about then?

I then tried starting with the symetric part, yet I still can't figure it out, the app just has a an NSTextField and a button that will either encrypt or decrypt the text in it. I do that like this

//Action for encrypt button press
- (IBAction)buttonPress:(NSButton *)sender {
    [[self button] setTitle:[self isEncrytped] ? @"Encrypt" : @"Decrypt"];
    [[self text] setEditable:[self isEncrypted]];

    if (self.isEncrypted) {
        [self encrypt];
    } else {
        [self decrypt];
    }

    self.isEncrypted = ![self isEncrypted];
}
- (void)encrypt {
    CFErrorRef error = NULL;

    NSData* data = [[[self text] stringValue] dataUsingEncoding:NSUTF8StringEncoding];
    SecTransformRef encrypt = SecEncryptTransformCreate([self key], &error);

    if (error) {
        CFShow(error);
    }

    SecTransformSetAttribute(encrypt, kSecTransformInputAttributeName, (__bridge CFTypeRef _Nonnull)(data), NULL);
    if (error) {
        CFShow(error);
    }

    data = SecTransformExecute(encrypt, &error);
    if (error) {
        CFShow(error);
    }
}
- (void)decrypt {
    CFErrorRef error = NULL;

    SecTransformRef decrypt = SecDecryptTransformCreate([self key], &error);
    if (error) {
        CFShow(error);
    }

    SecTransformSetAttribute(decrypt, kSecTransformInputAttributeName, [self data], &error);

    if (error) {
        CFShow(error);
    }

    self.data = SecTransformExecute(decrypt, &error);

    if (error) {
        CFShow(error);
    }
}

It just keeps crashing for some reason, also the errors are useless as they don't even get to execute.

So in short my question is how to do asymmetric encription in OS X, and additionally why doing symmetric encryption crashes?

Update

So I finally got the

CFErrorRef

s to work (not sure how: I just reopened Xcode) and this is what I got:

Error Domain=com.apple.security.transforms.error Code=14
"Can not execute ILEFCMMMU-Decrypt Transform, missing required attributes: INPUT"
UserInfo={NSDescription=Can not execute ILEFCMMMU-Decrypt Transform, missing required attributes: INPUT}

I am not sure why It says

ILEFCMMMU-Decrypt Transform

if I am using an encrypt transform not decrypt (yes I double checked that).

And for decrypting it just crashes.

Update 2

I found out my encrypt and decrypt calls where flipped, so I was trying to encrypt when it was encrypted and decrypt when it was decrypted. That explains the message in update 1, but not it crashes when I try to encrypt. I tracked the error down and found out

SecTransformExecute

is where the crash occurs, it appears that my cast to

NSData

or something is wrong because using

CFStringRef string = (__bridge CFStringRef)([[self texto] stringValue]);
...
SecTransformSetAttribute(encriptar, kSecTransformInputAttributeName, string, NULL);

doesn't crash, but now the Text Field is replaced with an empty string.