(Objective-C) IMAP Download and Verify Signed MIME

Downloads the original MIME of a digitally signed email and saves the .p7s signature along with other MIME parts. It then imports the email into a Chilkat email object to unwrap the S/MIME and verify the signature, and subsequently saves the attachments if they haven't been saved already.

Note: This example requires Chilkat v11.0.0 or greater.

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#import <CkoImap.h>
#import <CkoStringBuilder.h>
#import <CkoMime.h>
#import <CkoStringTable.h>
#import <CkoEmail.h>
#import <CkoCert.h>

BOOL success = NO;

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

CkoImap *imap = [[CkoImap alloc] init];

// Connect to an IMAP server.
// Use TLS
imap.Ssl = YES;
imap.Port = [NSNumber numberWithInt:993];
success = [imap Connect: @"imap.example.com"];
if (success == NO) {
    NSLog(@"%@",imap.LastErrorText);
    return;
}

success = [imap Login: @"myLogin" password: @"myPassword"];
if (success == NO) {
    NSLog(@"%@",imap.LastErrorText);
    return;
}

// Select an IMAP mailbox
success = [imap SelectMailbox: @"Inbox"];
if (success == NO) {
    NSLog(@"%@",imap.LastErrorText);
    return;
}

// Download the 1st email (as MIME) in the Inbox by sequence number.
CkoStringBuilder *sbMime = [[CkoStringBuilder alloc] init];
success = [imap FetchSingleAsMimeSb: 1 bUid: NO sbMime: sbMime];
if (success == NO) {
    NSLog(@"%@",imap.LastErrorText);
    return;
}

// Load it into a MIME object and check to see if it is signed
CkoMime *mime = [[CkoMime alloc] init];
[mime LoadMimeSb: sbMime];
BOOL alreadySavedParts = NO;
if ([mime ContainsSignedParts] == YES) {

    // This will save the .p7s and other parts...
    CkoStringTable *st = [[CkoStringTable alloc] init];
    success = [mime PartsToFiles: @"c:/temp/qa_output" st: st];
    if (success == YES) {
        int numFiles = [st.Count intValue];
        int i = 0;
        while (i < numFiles) {
            NSLog(@"%@%@",@"Created: ",[st StringAt: [NSNumber numberWithInt: i]]);
            i = i + 1;
        }

        alreadySavedParts = YES;
    }

}

// Load the MIME into an Email object.  This unwraps the security layers and verifies signatures.
CkoEmail *email = [[CkoEmail alloc] init];
[email SetFromMimeSb: sbMime];

if (email.ReceivedSigned == YES) {

    NSLog(@"%@",@"This email was signed.");

    // Check to see if the signatures were verified.
    if (email.SignaturesValid == YES) {
        NSLog(@"%@",@"Digital signature(s) verified.");

        NSLog(@"%@%@",@"Signer: ",email.SignedBy);

        // The certificate used for signing may be obtained
        // by calling email.GetSignedByCert.
        CkoCert *cert = [[CkoCert alloc] init];
        success = [email LastSignerCert: [NSNumber numberWithInt: i] cert: cert];
        if (success == NO) {
            NSLog(@"%@",@"Failed to get signing certificate object.");
        }
        else {
            NSLog(@"%@%@",@"Signing cert: ",cert.SubjectCN);
        }

    }

}
else {
    NSLog(@"%@",@"Digital signature verification failed.");
}

if (alreadySavedParts != YES) {
    [email SaveAllAttachments: @"c:/temp/qa_output"];
}