Marc Schlösser Marc Schlösser - 1 year ago 490
iOS Question

SecCertificateRef: How to get the certificate information?

I have a certificate (SecCertificateRef), I can check if it's valid and I can extract a "summary" using SecCertificateCopySubjectSummary.

What is the "summary" exactly? I don't understand the term "A string that contains a human-readable summary of the contents of the certificate." in the Apple documentation. I think, they mean the "CN" in the certificate, correct?

Is there any method to get the clear X509-information out of SecCertificateRef? Does a cast to a keychain-object help?

I want to have something like this and I am especially focussed on the "CN" to compare it with the URL I submitted to avoid man-in-the-middle attacks. (Or any better ideas?)

That is what I want to have:

Version: 3 (0x2)
Serial Number: 1 (0x1)
Signature Algorithm: md5WithRSAEncryption
Issuer: C=XY, ST=Austria, L=Graz, O=TrustMe Ltd, OU=Certificate Authority, CN=CA/Email=ca@trustme.dom
Not Before: Oct 29 17:39:10 2000 GMT
Not After : Oct 29 17:39:10 2001 GMT
Subject: C=DE, ST=Austria, L=Vienna, O=Home, OU=Web Lab,
Subject Public Key Info:
Public Key Algorithm: rsaEncryption
RSA Public Key: (1024 bit)
Modulus (1024 bit):
Exponent: 65537 (0x10001)
X509v3 extensions:
X509v3 Subject Alternative Name:
Netscape Comment:
mod_ssl generated test server certificate
Netscape Cert Type:
SSL Server
Signature Algorithm: md5WithRSAEncryption

Answer Source

I couldn't wait for an answer to the bounty, so I found a solution myself. As others said, Security.framework doesn't give you a way to get this information, so you need to ask OpenSSL to parse the certificate data for you:

#import <openssl/x509.h>

// ...

NSData *certificateData = (NSData *) SecCertificateCopyData(certificate);

const unsigned char *certificateDataBytes = (const unsigned char *)[certificateData bytes];
X509 *certificateX509 = d2i_X509(NULL, &certificateDataBytes, [certificateData length]);

NSString *issuer = CertificateGetIssuerName(certificateX509);
NSDate *expiryDate = CertificateGetExpiryDate(certificateX509);

Where CertificateGetIssuerName and CertificateGetExpiryDate are as follows:

static NSString * CertificateGetIssuerName(X509 *certificateX509)
    NSString *issuer = nil;
    if (certificateX509 != NULL) {
        X509_NAME *issuerX509Name = X509_get_issuer_name(certificateX509);

        if (issuerX509Name != NULL) {
            int nid = OBJ_txt2nid("O"); // organization
            int index = X509_NAME_get_index_by_NID(issuerX509Name, nid, -1);

            X509_NAME_ENTRY *issuerNameEntry = X509_NAME_get_entry(issuerX509Name, index);

            if (issuerNameEntry) {
                ASN1_STRING *issuerNameASN1 = X509_NAME_ENTRY_get_data(issuerNameEntry);

                if (issuerNameASN1 != NULL) {
                    unsigned char *issuerName = ASN1_STRING_data(issuerNameASN1);
                    issuer = [NSString stringWithUTF8String:(char *)issuerName];

    return issuer;

static NSDate *CertificateGetExpiryDate(X509 *certificateX509)
    NSDate *expiryDate = nil;

    if (certificateX509 != NULL) {
        ASN1_TIME *certificateExpiryASN1 = X509_get_notAfter(certificateX509);
        if (certificateExpiryASN1 != NULL) {
            ASN1_GENERALIZEDTIME *certificateExpiryASN1Generalized = ASN1_TIME_to_generalizedtime(certificateExpiryASN1, NULL);
            if (certificateExpiryASN1Generalized != NULL) {
                unsigned char *certificateExpiryData = ASN1_STRING_data(certificateExpiryASN1Generalized);

                // ASN1 generalized times look like this: "20131114230046Z"
                //                                format:  YYYYMMDDHHMMSS
                //                               indices:  01234567890123
                //                                                   1111
                // There are other formats (e.g. specifying partial seconds or 
                // time zones) but this is good enough for our purposes since
                // we only use the date and not the time.
                // (Source:

                NSString *expiryTimeStr = [NSString stringWithUTF8String:(char *)certificateExpiryData];
                NSDateComponents *expiryDateComponents = [[NSDateComponents alloc] init];

                expiryDateComponents.year   = [[expiryTimeStr substringWithRange:NSMakeRange(0, 4)] intValue];
                expiryDateComponents.month  = [[expiryTimeStr substringWithRange:NSMakeRange(4, 2)] intValue];
          = [[expiryTimeStr substringWithRange:NSMakeRange(6, 2)] intValue];
                expiryDateComponents.hour   = [[expiryTimeStr substringWithRange:NSMakeRange(8, 2)] intValue];
                expiryDateComponents.minute = [[expiryTimeStr substringWithRange:NSMakeRange(10, 2)] intValue];
                expiryDateComponents.second = [[expiryTimeStr substringWithRange:NSMakeRange(12, 2)] intValue];

                NSCalendar *calendar = [NSCalendar currentCalendar];
                expiryDate = [calendar dateFromComponents:expiryDateComponents];

                [expiryDateComponents release];

    return expiryDate;

I only actually needed the issuer's organization name and the expiry date for my purposes, so that's all the code I've included below. But, based on this you should be able to figure out the rest by reading the x509.h header file.


Here's how to get the certificate. I haven't put any error handling, etc. You'll want to check trustResult, err, etc., for example.

NSURLAuthenticationChallenge *challenge;
SecTrustResultType trustResult;
SecTrustRef trust = challenge.protectionSpace.serverTrust;
OSStatus err = SecTrustEvaluate(trust, &trustResult);
SecCertificateRef certificate = SecGetLeafCertificate(trust); // See Apple docs for implementation of SecGetLeafCertificate