Example of direct OpenSSL usage in Swift

ssltest.swift

//
//  ssltest.swift
//
//  Created by Cardasis, Jon C. (CAC) on 1/22/18.
//  Copyright © 2018 Jon Cardasis. All rights reserved.
//

import OpenSSL
import Security

/// Create typealias' for macros not imported to Swift
fileprivate typealias X509 = OpaquePointer


public class X509Certificate {
    
    public static func issuerName(for certificate: SecCertificate) -> String? {
        let data = SecCertificateCopyData(certificate) as NSData

        var firstByte: UnsafePointer? = data.bytes.assumingMemoryBound(to: UInt8.self)
        let certificateX509: X509? = d2i_X509(nil, &firstByte, data.length)
        
        let issuer = issuerName(for: certificateX509)

        X509_free(certificateX509)
        return issuer
    }
    
    
    //MARK: - Private
    
    private static func issuerName(for x509Certificate: X509?) -> String? {
        var issuer: String?
        guard let x509Certificate = x509Certificate else {
            return nil
        }
        
        let issuerName = X509_get_issuer_name(x509Certificate)
        let nid = NID_commonName
        let index = X509_NAME_get_index_by_NID(issuerName, nid, -1)
        
        if let issuerNameEntry /*X509_NAME_ENTRY*/ = X509_NAME_get_entry(issuerName, index) {
            if let issuerNameASN1 = X509_NAME_ENTRY_get_data(issuerNameEntry),
                let issuerNameUTF8 = ASN1_STRING_get0_data(issuerNameASN1) { // string rep of DES ASN1 structure
                issuer = String(cString: issuerNameUTF8)
            }
        }
        return issuer
    }
}