Objective-C

Get the S/MIME Signer's Certificate

Demonstrates the Chilkat Mime.LastSignerCert method, which loads the signer certificate at a zero-based index from the most recent successful verification (or security-unwrapping) into a Cert. The first argument is the signer index and the second is the receiving Cert.

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: Verifying tells you the signature is mathematically valid, but you usually also need to know who signed — the subject, the issuer, the validity dates — to decide whether to trust it. This retrieves each signer's certificate after verification so your code can inspect and apply its own trust rules. A message can have multiple signers, so iterate from 0 to NumSignerCerts - 1.

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Objective-C

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

BOOL success = NO;

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

//  After a successful verification, load each signer's certificate to inspect it.  The 1st argument
//  is the zero-based signer index and the 2nd is a Cert object that receives the certificate.
success = [mime Verify];
if (success != YES) {
    NSLog(@"%@",mime.LastErrorText);
    return;
}

int n = [mime.NumSignerCerts intValue];
CkoCert *cert = [[CkoCert alloc] init];
int i;
for (i = 0; i <= n - 1; i++) {
    success = [mime LastSignerCert: [NSNumber numberWithInt: i] cert: cert];
    if (success == NO) {
        NSLog(@"%@",mime.LastErrorText);
        return;
    }

    NSLog(@"%@%d%@%@%@%@%@",@"Signer ",i,@": ",cert.SubjectCN,@" (issued by ",cert.IssuerCN,@")");
}