RSAParameters to pfx (X509Certificate2) conversion

Question

I want to create a pfx file from keys created by RSACryptoServiceProvider . I tried:

certificate.PrivateKey =  rsa as AsymmetricAlgorithm;

which is the reverse of:

rsa = (RSACryptoServiceProvider)certificate.PrivateKey;

which seems to work (the second, that is). But got the following error:

m_safeCertContext is an invalid handle.

I tried some things using RSAParameters - but to no avail.

Answer 1

You can use Bouncy Castle to do it:

private static byte[] MergePFXFromPrivateAndCertificate(RSAParameters privateKey, X509Certificate2 certificate, string pfxPassPhrase)
{
    RsaPrivateCrtKeyParameters rsaParam = new RsaPrivateCrtKeyParameters(
        ParseAsUnsignedBigInteger(privateKey.Modulus),
        ParseAsUnsignedBigInteger(privateKey.Exponent),
        ParseAsUnsignedBigInteger(privateKey.D),
        ParseAsUnsignedBigInteger(privateKey.P),
        ParseAsUnsignedBigInteger(privateKey.Q),
        ParseAsUnsignedBigInteger(privateKey.DP),
        ParseAsUnsignedBigInteger(privateKey.DQ),
        ParseAsUnsignedBigInteger(privateKey.InverseQ)
    );

    Org.BouncyCastle.X509.X509Certificate bcCert = new Org.BouncyCastle.X509.X509CertificateParser().ReadCertificate(certificate.RawData);

    MemoryStream p12Stream = new MemoryStream();
    Pkcs12Store p12 = new Pkcs12Store();
    p12.SetKeyEntry("key", new AsymmetricKeyEntry(rsaParam), new X509CertificateEntry[] { new X509CertificateEntry(bcCert) });
    p12.Save(p12Stream, pfxPassPhrase.ToCharArray(), new SecureRandom());

    return p12Stream.ToArray();
}

private static BigInteger ParseAsUnsignedBigInteger(byte[] rawUnsignedNumber)
{
    return new BigInteger(1, rawUnsignedNumber, 0, rawUnsignedNumber.Length);
}

You will need the following namespaces:

using Org.BouncyCastle.Crypto.Parameters;
using Org.BouncyCastle.Math;
using Org.BouncyCastle.Pkcs;
using Org.BouncyCastle.Security;
using System.Security.Cryptography;
using System.Security.Cryptography.X509Certificates;