(Objective-C) S/MIME Decrypt using Certificate and Private Key in Apple Keychain

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Decrypts S/MIME using a certificate with private key found in the Apple Keychain.

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#import <CkoCert.h>
#import <CkoMime.h>

CkoCert *cert = [[CkoCert alloc] init];

// Load the certificate to be used for decryption by the Subject Common Name
// On MacOS and iOS, Chilkat will search the Keychain(s) for the matching certificate.
// Note: The private key must be present to decrypt.
BOOL success = [cert LoadByCommonName: @"My Cert"];
if (success == NO) {
    NSLog(@"%@",cert.LastErrorText);
    return;
}

NSLog(@"%@%d",@"Cert has private key: ",[cert HasPrivateKey]);

// Load the MIME to be decrypted.
// We encrypted using this example:  S/MIME Encrypt using Certificate in Apple Keychain
CkoMime *mime = [[CkoMime alloc] init];
success = [mime LoadMimeFile: @"./encrypted.mime"];
if (success == NO) {
    NSLog(@"%@",mime.LastErrorText);
    return;
}

NSLog(@"%@",[mime GetMime]);
NSLog(@"%@",@"----");

// Here's the encrypted MIME:

// Subject: test
// SomeHeader: 123
// Content-Type: application/x-pkcs7-mime; name="smime.p7m"; smime-type="enveloped-data"
// Content-Disposition: attachment; filename="smime.p7m"
// Content-Transfer-Encoding: base64
// 
// MIICSwYJKoZIhvcNAQcDoIICPDCCAjgCAQAxggGzMIIBrwIBADCBljCBgTELMAkGA1UEBhMCSVQx
// EDAOBgNVBAgMB0JlcmdhbW8xGTAXBgNVBAcMEFBvbnRlIFNhbiBQaWV0cm8xFzAVBgNVBAoMDkFj
// dGFsaXMgUy5wLkEuMSwwKgYDVQQDDCNBY3RhbGlzIENsaWVudCBBdXRoZW50aWNhdGlvbiBDQSBH
// MwIQPCWvkSv8oQ7xRmEHJ6TzEDANBgkqhkiG9w0BAQEFAASCAQB3VZvHRE5EWxug7Sckpcz1ucDZ
// YiTKiqmyPt75MhzNRQLtKFx/jWwlemUwnPMzeu6yutCkZ74Bdn7MBsfDqV3bUz43wAu+fRBteGvF
// mTc00MfY8L7o8dkpj4AqAOCj4hKQzbSE99GvSzyXcPE2Gm5NrOPtKxqfFqbBRTCb4fBZP84LaL+x
// rnYfrM4qXTppixyN8iFYCd4maEbMu/GA5o+j0BkDDnx42pILDoAGV/ERyx55Y3Nc2Mhm/cITBMNn
// g7uS9KPrlYizNaqVu09Hi9jg4gdZaRiTjUqg05tSOk/YqIQxTgfscwSPY92/ewpI6e1EHtLt8Q33
// gWCbERptSntUMHwGCSqGSIb3DQEHATAdBglghkgBZQMEAQIEENm1AxeXlEMx7p6McjHIj5CAUEQj
// 0GuJ5LnTqiqIjOiwmwNidl1N1TRluxX5vAQvwBuYE6bQK4+i04yn2Av3cucW4kvxgP2Nmni+XgQt
// aPPKlasaVceEeZ15IYjw77/m3YYn

// -------------------------------------
// Decrypt the MIME.
success = [mime DecryptUsingCert: cert];
if (success == NO) {
    NSLog(@"%@",mime.LastErrorText);
    return;
}

// -------------------------------------
// Note: A password dialog may be shown, possibly twice, when accessing the private key.
// See the following blog post explaining how to suppress the dialog:
// Suppress Password Dialog when Accessing Private Key in Apple Keychain

// Show the unencrypted MIME
NSLog(@"%@",[mime GetMime]);

// Here's the decrypted MIME

// Subject: test
// SomeHeader: 123
// Content-Type: text/plain
// 
// This is the body.