Objective-C

Add an S/MIME Detached Signature

Demonstrates the Chilkat Mime.AddDetachedSignature method, which creates an S/MIME detached signature. The only argument is the signing Cert, which must have access to its private key. On success the entity becomes a multipart/signed with the content and a separate signature part.

Note: The file paths are relative to the application's current working directory. Absolute paths may also be used. Supply the paths appropriate to your own environment.

Background: A detached signature (multipart/signed) keeps the original content readable alongside a separate signature part — so recipients whose software does not understand S/MIME still see the message, they just cannot verify it. That backward compatibility makes detached the usual choice for signed email. The signer proves authorship with a certificate that carries its private key.

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Objective-C

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

BOOL success = NO;

CkoMime *mime = [[CkoMime alloc] init];
success = [mime SetBodyFromPlainText: @"This message will be signed."];
if (success == NO) {
    NSLog(@"%@",mime.LastErrorText);
    return;
}

//  Load the signing certificate (which must have access to its private key) from a PFX file.
//  The PFX password should come from a secure source rather than being hard-coded.
NSString *pfxPassword = @"myPfxPassword";
CkoCert *cert = [[CkoCert alloc] init];
success = [cert LoadPfxFile: @"qa_data/signer.pfx" password: pfxPassword];
if (success == NO) {
    NSLog(@"%@",cert.LastErrorText);
    return;
}

//  Create an S/MIME detached signature.  The object becomes a multipart/signed entity with the
//  original content and a separate signature part.
success = [mime AddDetachedSignature: cert];
if (success == NO) {
    NSLog(@"%@",mime.LastErrorText);
    return;
}

success = [mime SaveMime: @"qa_output/signed.eml"];
if (success == NO) {
    NSLog(@"%@",mime.LastErrorText);
    return;
}

NSLog(@"%@",@"Detached signature added.");