(Swift 3,4,5...) Duplicate openssl req -newkey rsa:2048 -nodes -keyout mydomain.pem -out mydomain.csr

Demonstrates how to duplicate this OpenSSL command:

openssl req -newkey rsa:2048 -nodes -keyout mydomain.pem -out mydomain.csr

This command creates 2 files:

1. mydomain.csr: this is the file to send to DigiCert or Let's Encrypt (or any other CA)
2. mydomain.pem: this is the private key of the domain.

The second file is needed to pair with the certificate that will later be received from the CA.

Chilkat Downloads for the Swift Programming Language MAC OS X (Cocoa) Objective-C/Swift Libs iOS Objective-C/Swift Libs

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

    let rsa = CkoRsa()!

    // Generate a 2048-bit key.  Chilkat RSA supports
    // key sizes ranging from 512 bits to 8192 bits.
    var success: Bool = rsa.generateKey(2048)
    if success != true {
        print("\(rsa.lastErrorText!)")
        return
    }

    var privKey: CkoPrivateKey? = rsa.exportPrivateKeyObj()

    // Save the private key to unencrypted PKCS8 PEM
    success = privKey!.savePkcs8PemFile("mydomain.pem")

    // (alternatively) Save the private key to encrypted PKCS8 PEM
    success = privKey!.savePkcs8EncryptedPemFile("myPassword", path: "mydomain_enc.pem")

    // We'll need the private key's modulus for the CSR.
    // The modulus is not something that needs to be protected.  Most people don't realize
    // that a public key is actually just a subset of the private key.  The public parts of
    // an RSA private key are the modulus and exponent.  The exponent is always 65537.
    let privKeyXml = CkoXml()!
    success = privKeyXml.load(privKey!.getXml())

    // Get the modulus in base64 format:
    var keyModulus: String? = privKeyXml.getChildContent("Modulus")

    // --------------------------------------------------------------------------------
    // Now build the CSR using Chilkat's ASN.1 API.
    // The keyModulus will be embedded within the ASN.1.

    // A new ASN.1 object is automatically a SEQUENCE.
    // Given that the CSR's root item is a SEQUENCE, we can use
    // this as the root of our CSR.
    let asnRoot = CkoAsn()!

    // Beneath the root, we have a SEQUENCE (the certificate request info), 
    // another SEQUENCE (the algorithm identifier), and a BITSTRING (the signature data)

    success = asnRoot.appendSequence()
    success = asnRoot.appendSequence()

    // ----------------------------------
    // Build the Certificate Request Info
    // ----------------------------------
    var asnCertReqInfo: CkoAsn? = asnRoot.getSubItem(0)
    success = asnCertReqInfo!.appendInt(0)

    // Build the Subject part of the Certificate Request Info
    var asnCertSubject: CkoAsn? = asnCertReqInfo!.appendSequenceR()

    // Add each subject part..
    var asnTemp: CkoAsn? = asnCertSubject!.appendSetR()
    success = asnTemp!.appendSequence2()
    // AppendSequence2 updates the internal reference to the newly appended SEQUENCE.
    // The OID and printable string are added to the SEQUENCE.
    success = asnTemp!.appendOid("2.5.4.6")
    success = asnTemp!.append("printable", value: "US")
    asnTemp = nil

    asnTemp = asnCertSubject!.appendSetR()
    success = asnTemp!.appendSequence2()
    success = asnTemp!.appendOid("2.5.4.8")
    success = asnTemp!.append("utf8", value: "Utah")
    asnTemp = nil

    asnTemp = asnCertSubject!.appendSetR()
    success = asnTemp!.appendSequence2()
    success = asnTemp!.appendOid("2.5.4.7")
    success = asnTemp!.append("utf8", value: "Lindon")
    asnTemp = nil

    asnTemp = asnCertSubject!.appendSetR()
    success = asnTemp!.appendSequence2()
    success = asnTemp!.appendOid("2.5.4.10")
    success = asnTemp!.append("utf8", value: "DigiCert Inc.")
    asnTemp = nil

    asnTemp = asnCertSubject!.appendSetR()
    success = asnTemp!.appendSequence2()
    success = asnTemp!.appendOid("2.5.4.11")
    success = asnTemp!.append("utf8", value: "DigiCert")
    asnTemp = nil

    asnTemp = asnCertSubject!.appendSetR()
    success = asnTemp!.appendSequence2()
    success = asnTemp!.appendOid("2.5.4.3")
    success = asnTemp!.append("utf8", value: "example.digicert.com")
    asnTemp = nil

    asnCertSubject = nil

    // Build the Public Key Info part of the Certificate Request Info
    var asnPubKeyInfo: CkoAsn? = asnCertReqInfo!.appendSequenceR()

    var asnPubKeyAlgId: CkoAsn? = asnPubKeyInfo!.appendSequenceR()
    success = asnPubKeyAlgId!.appendOid("1.2.840.113549.1.1.1")
    success = asnPubKeyAlgId!.appendNull()
    asnPubKeyAlgId = nil

    // The public key itself is a BIT STRING, but the bit string is composed of ASN.1
    // for the RSA public key.  We'll first build the RSA ASN.1 for the public key
    // (containing the 2048 bit modulus and exponent), and encoded it to DER, and then add
    // the DER bytes as a BIT STRING (as a sub-item of asnPubKeyInfo)

    // This is already a SEQUENCE..
    let asnRsaKey = CkoAsn()!

    // The RSA modulus is a big integer.
    success = asnRsaKey.appendBigInt(keyModulus, encoding: "base64")
    success = asnRsaKey.appendInt(65537)

    var rsaKeyDerBase64: String? = asnRsaKey.getEncodedDer("base64")

    // Now add the RSA key DER as a BIT STRING.
    success = asnPubKeyInfo!.appendBits(rsaKeyDerBase64, encoding: "base64")
    asnPubKeyInfo = nil

    // The last part of the certificate request info is an empty context-specific constructed item
    // with a tag equal to 0.
    success = asnCertReqInfo!.appendContextConstructed(0)

    // Get the DER of the asnCertReqInfo.  
    // This will be signed using the RSA private key.
    let bdDer = CkoBinData()!
    success = asnCertReqInfo!.writeBd(bdDer)

    // Add the signature to the ASN.1
    let bdSig = CkoBinData()!
    success = rsa.signBd(bdDer, hashAlgorithm: "SHA1", bdSig: bdSig)
    success = asnRoot.appendBits(bdSig.getEncoded("base64"), encoding: "base64")

    asnCertReqInfo = nil

    // ----------------------------------
    // Finally, add the algorithm identifier, which is the 2nd sub-item under the root.
    // ----------------------------------
    var asnAlgId: CkoAsn? = asnRoot.getSubItem(1)
    success = asnAlgId!.appendOid("1.2.840.113549.1.1.5")
    success = asnAlgId!.appendNull()
    asnAlgId = nil

    // Write the CSR to a DER encoded binary file:
    success = asnRoot.writeBinaryDer("qa_output/mydomain.csr")
    if success != true {
        print("\(asnRoot.lastErrorText!)")
        return
    }

    // It is also possible to get the CSR in base64 format:
    var csrBase64: String? = asnRoot.getEncodedDer("base64")

    print("Base64 CSR:")
    print("\(csrBase64!)")

    privKey = nil

}