Objective-C

Check if an Email Was Received Digitally Signed

Demonstrates the read-only Chilkat Email.ReceivedSigned property, which is true if the email was originally received carrying one or more digital signatures. Knowing a message was signed is separate from knowing the signature checked out, so this example also reads SignaturesValid to report whether the signed content verified.

Background: A digital signature on an email (S/MIME) provides two things: authenticity (it was really sent by the holder of a particular certificate) and integrity (the content was not altered in transit). The sender signs a hash of the message with their private key; the recipient verifies it with the sender's public certificate. ReceivedSigned simply tells you a signature is present — verifying it is a separate step exposed through SignaturesValid.

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Objective-C

#import <CkoEmail.h>

BOOL success = NO;

//  Demonstrates the read-only Email.ReceivedSigned property, which is true if this
//  email was originally received with a digital signature.  Use SignaturesValid to
//  determine whether the signed content actually verified.

CkoEmail *email = [[CkoEmail alloc] init];

success = [email LoadEml: @"qa_data/eml/signed.eml"];
if (success == NO) {
    NSLog(@"%@",email.LastErrorText);
    return true;
}

if (email.ReceivedSigned == YES) {
    NSLog(@"%@",@"This email was received with a digital signature.");
    if (email.SignaturesValid == YES) {
        NSLog(@"%@",@"All signatures are valid.");
    }
    else {
        NSLog(@"%@",@"One or more signatures are NOT valid.");
    }

}
else {
    NSLog(@"%@",@"This email was not signed.");
}

//  Note: Paths such as "qa_data/..." are relative local filesystem paths,
//  relative to the current working directory of the running application.