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

Chilkat.Rsa rsa = new Chilkat.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) {
    Debug.WriteLine(rsa.LastErrorText);
    return;
}

Chilkat.PrivateKey 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.
Chilkat.Xml privKeyXml = new Chilkat.Xml();
success = privKeyXml.LoadXml(privKey.GetXml());

// Get the modulus in base64 format:
string 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.
Chilkat.Asn asnRoot = new Chilkat.Asn();

// 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
// ----------------------------------
Chilkat.Asn asnCertReqInfo = asnRoot.GetSubItem(0);
success = asnCertReqInfo.AppendInt(0);

// Build the Subject part of the Certificate Request Info
Chilkat.Asn asnCertSubject = asnCertReqInfo.AppendSequenceR();

// Add each subject part..
Chilkat.Asn 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");

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

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

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

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

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

// Build the Public Key Info part of the Certificate Request Info
Chilkat.Asn asnPubKeyInfo = asnCertReqInfo.AppendSequenceR();

Chilkat.Asn asnPubKeyAlgId = asnPubKeyInfo.AppendSequenceR();
success = asnPubKeyAlgId.AppendOid("1.2.840.113549.1.1.1");
success = asnPubKeyAlgId.AppendNull();

// 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..
Chilkat.Asn asnRsaKey = new Chilkat.Asn();

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

string rsaKeyDerBase64 = asnRsaKey.GetEncodedDer("base64");

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

// 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.
Chilkat.BinData bdDer = new Chilkat.BinData();
success = asnCertReqInfo.WriteBd(bdDer);

// Add the signature to the ASN.1
Chilkat.BinData bdSig = new Chilkat.BinData();
success = rsa.SignBd(bdDer,"SHA1",bdSig);
success = asnRoot.AppendBits(bdSig.GetEncoded("base64"),"base64");

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

// Write the CSR to a DER encoded binary file:
success = asnRoot.WriteBinaryDer("qa_output/mydomain.csr");
if (success != true) {
    Debug.WriteLine(asnRoot.LastErrorText);
    return;
}

// It is also possible to get the CSR in base64 format:
string csrBase64 = asnRoot.GetEncodedDer("base64");

Debug.WriteLine("Base64 CSR:");
Debug.WriteLine(csrBase64);