(Objective-C) Add DomainKey-Signature Header to MIME / Email

Demonstrates how to add a DomainKey-Signature header field to a MIME message.

Note: The DKIM / DomainKey functionality is included with the Chilkat MIME license.

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#import <CkoDkim.h>
#import <NSString.h>
#import <CkoFileAccess.h>

// This example requires the Chilkat API to have been previously unlocked.
// See Global Unlock Sample for sample code.

CkoDkim *dkim = [[CkoDkim alloc] init];

// To create a DomainKey signature for email (i.e. MIME),
// you'll need to provide the following:
// (1) An RSA private key in any common file format.
// (2) The domain name (typically the same domain
// as the sender of an email).
// (3) A selector for the domain name -- an arbitrary string
// to identify the matching public key in DNS.

// To allow an email recipient to verify the DomainKey signature via an
// external email client supporting DomainKey or using other software,
// you will need to create a DNS record with the selector
// and matching public key.  This example does not provide
// information about DomainKey DNS record creation.  
// (Chilkat does not provide an API for creating DNS records.  
// Creating the DomainKey DNS record is something you would do
// manually.)

// Set the domain and selector:
// You'll need to provide your own values here..
dkim.DomainKeyDomain = @"chilkatsoft.com";
dkim.DomainKeySelector = @"salmon";

// Load a private key from any common RSA private key
// format, such as DER, PKCS8, PEM, XML, etc.
// The LoadDomainKeyPkFile method automatically detects
// the file format and reads it appropriately.
// If a password is not required, you'll still need to provide
// a password string argument, but it is ignored.
NSString *password = 0;
password = @"optionalPassword";
BOOL success = [dkim LoadDomainKeyPkFile: @"myPrivateKey.pem" optionalPassword: password];
if (success != YES) {
    NSLog(@"%@",dkim.LastErrorText);
    return;
}

// Load a MIME file into a byte array.
CkoFileAccess *fac = [[CkoFileAccess alloc] init];
NSData mimeData;
mimeData = [fac ReadEntireFile: @"testMessage.eml"];
if (fac.LastMethodSuccess != YES) {
    NSLog(@"%@",fac.LastErrorText);
    return;
}

// Sign it.  This adds the DomainKey-Signature header and
// returns the new MIME with DomainKey-Signature added.
NSData domainKeySignedMime;
domainKeySignedMime = [dkim AddDomainKeySignature: mimeData];
if (dkim.LastMethodSuccess != YES) {
    NSLog(@"%@",dkim.LastErrorText);
    return;
}

success = [fac WriteEntireFile: @"domainKeySigned.eml" fileData: domainKeySignedMime];
if (success != YES) {
    NSLog(@"%@",fac.LastErrorText);
    return;
}

NSLog(@"%@",@"Success.");