(C++) 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.

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#include <CkRsa.h>
#include <CkPrivateKey.h>
#include <CkXml.h>
#include <CkAsn.h>
#include <CkBinData.h>

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

    CkRsa rsa;

    // Generate a 2048-bit key.  Chilkat RSA supports
    // key sizes ranging from 512 bits to 8192 bits.
    bool success = rsa.GenerateKey(2048);
    if (success != true) {
        std::cout << rsa.lastErrorText() << "\r\n";
        return;
    }

    CkPrivateKey *privKey = 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","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.
    CkXml privKeyXml;
    success = privKeyXml.LoadXml(privKey->getXml());

    // Get the modulus in base64 format:
    const char *keyModulus = 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.
    CkAsn asnRoot;

    // 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
    // ----------------------------------
    CkAsn *asnCertReqInfo = asnRoot.GetSubItem(0);
    success = asnCertReqInfo->AppendInt(0);

    // Build the Subject part of the Certificate Request Info
    CkAsn *asnCertSubject = asnCertReqInfo->AppendSequenceR();

    // Add each subject part..
    CkAsn *asnTemp = 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->AppendString("printable","US");
    delete asnTemp;

    asnTemp = asnCertSubject->AppendSetR();
    success = asnTemp->AppendSequence2();
    success = asnTemp->AppendOid("2.5.4.8");
    success = asnTemp->AppendString("utf8","Utah");
    delete asnTemp;

    asnTemp = asnCertSubject->AppendSetR();
    success = asnTemp->AppendSequence2();
    success = asnTemp->AppendOid("2.5.4.7");
    success = asnTemp->AppendString("utf8","Lindon");
    delete asnTemp;

    asnTemp = asnCertSubject->AppendSetR();
    success = asnTemp->AppendSequence2();
    success = asnTemp->AppendOid("2.5.4.10");
    success = asnTemp->AppendString("utf8","DigiCert Inc.");
    delete asnTemp;

    asnTemp = asnCertSubject->AppendSetR();
    success = asnTemp->AppendSequence2();
    success = asnTemp->AppendOid("2.5.4.11");
    success = asnTemp->AppendString("utf8","DigiCert");
    delete asnTemp;

    asnTemp = asnCertSubject->AppendSetR();
    success = asnTemp->AppendSequence2();
    success = asnTemp->AppendOid("2.5.4.3");
    success = asnTemp->AppendString("utf8","example.digicert.com");
    delete asnTemp;

    delete asnCertSubject;

    // Build the Public Key Info part of the Certificate Request Info
    CkAsn *asnPubKeyInfo = asnCertReqInfo->AppendSequenceR();

    CkAsn *asnPubKeyAlgId = asnPubKeyInfo->AppendSequenceR();
    success = asnPubKeyAlgId->AppendOid("1.2.840.113549.1.1.1");
    success = asnPubKeyAlgId->AppendNull();
    delete asnPubKeyAlgId;

    // 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..
    CkAsn asnRsaKey;

    // The RSA modulus is a big integer.
    success = asnRsaKey.AppendBigInt(keyModulus,"base64");
    success = asnRsaKey.AppendInt(65537);

    const char *rsaKeyDerBase64 = asnRsaKey.getEncodedDer("base64");

    // Now add the RSA key DER as a BIT STRING.
    success = asnPubKeyInfo->AppendBits(rsaKeyDerBase64,"base64");
    delete asnPubKeyInfo;

    // 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.
    CkBinData bdDer;
    success = asnCertReqInfo->WriteBd(bdDer);

    // Add the signature to the ASN.1
    CkBinData bdSig;
    success = rsa.SignBd(bdDer,"SHA1",bdSig);
    success = asnRoot.AppendBits(bdSig.getEncoded("base64"),"base64");

    delete asnCertReqInfo;

    // ----------------------------------
    // Finally, add the algorithm identifier, which is the 2nd sub-item under the root.
    // ----------------------------------
    CkAsn *asnAlgId = asnRoot.GetSubItem(1);
    success = asnAlgId->AppendOid("1.2.840.113549.1.1.5");
    success = asnAlgId->AppendNull();
    delete asnAlgId;

    // Write the CSR to a DER encoded binary file:
    success = asnRoot.WriteBinaryDer("qa_output/mydomain.csr");
    if (success != true) {
        std::cout << asnRoot.lastErrorText() << "\r\n";
        return;
    }

    // It is also possible to get the CSR in base64 format:
    const char *csrBase64 = asnRoot.getEncodedDer("base64");

    std::cout << "Base64 CSR:" << "\r\n";
    std::cout << csrBase64 << "\r\n";

    delete privKey;
    }