(C#) Get a Certificate's Key Size

Demonstrates how to get the RSA key size of a certificate (for example, 1024-bit, 2048-bit, etc.)

Chilkat .NET Downloads Chilkat .NET Framework Chilkat for .NET Core

// For this example, I have a certificate in raw base64 format (not PEM),
// that looks like this:  "MIIGkDCCBHigAwIBAgIUMDA ... s/iqLsLA=="
Chilkat.StringBuilder sbCertBase64 = new Chilkat.StringBuilder();
bool success = sbCertBase64.LoadFile("qa_data/certs/base64Cert.txt","utf-8");

Chilkat.Cert cert = new Chilkat.Cert();
success = cert.LoadFromBase64(sbCertBase64.GetAsString());
if (success != true) {
    Debug.WriteLine(cert.LastErrorText);
    return;
}

// Get the public key.
Chilkat.PublicKey pubKey = cert.ExportPublicKey();
if (cert.LastMethodSuccess != true) {
    Debug.WriteLine(cert.LastErrorText);
    return;
}

// In Chilkat version v9.5.0.67, the KeySize property was added.
int numBits = pubKey.KeySize;
Debug.WriteLine("Number of bits = " + Convert.ToString(numBits));

// If using an older version of Chilkat, the key size can be obtained like this:
Chilkat.Xml xml = new Chilkat.Xml();
xml.LoadXml(pubKey.GetXml());

Chilkat.BinData binDat = new Chilkat.BinData();
binDat.AppendEncoded(xml.GetChildContent("Modulus"),"base64");

numBits = 8 * binDat.NumBytes;
Debug.WriteLine("Number of bits = " + Convert.ToString(numBits));