Objective-C

Check for an S/MIME Signing Time

Demonstrates the Chilkat Mime.HasSignatureSigningTime method, which returns whether the signer at a zero-based index included a CMS signingTime signed attribute. The only argument is the signer index; use NumSignerCerts for the count.

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 signing time records when the signer claims to have signed, which matters for auditing and for validating a certificate that has since expired. It is an optional signed attribute, so not every signature has one — this predicate lets you check before calling GetSignatureSigningTimeStr, avoiding an error for signers that omitted it. Being a signed attribute, it is covered by the signature and cannot be altered undetected.

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Objective-C

#import <CkoMime.h>

BOOL success = NO;

CkoMime *mime = [[CkoMime alloc] init];
success = [mime LoadMimeFile: @"qa_data/signed.eml"];
if (success == NO) {
    NSLog(@"%@",mime.LastErrorText);
    return;
}

//  After verifying, check whether each signer included a CMS signingTime signed attribute.  The
//  only argument is the zero-based signer index.
success = [mime Verify];
if (success != YES) {
    NSLog(@"%@",mime.LastErrorText);
    return;
}

int n = [mime.NumSignerCerts intValue];
int i;
for (i = 0; i <= n - 1; i++) {
    if ([mime HasSignatureSigningTime: [NSNumber numberWithInt: i]]) {
        NSLog(@"%@%d%@",@"Signer ",i,@" included a signing time.");
    }
    else {
        NSLog(@"%@%d%@",@"Signer ",i,@" did not include a signing time.");
    }

}