Exporting a Certificate as BASE-64 encoded .cer

Question

I am trying to export a cert without the private key as as BASE-64 encoded file, same as exporting it from windows. When exported from windows I am able to open the .cer file in notepad.

When I try the following and open on notepad I get binary data...I think it is...not readable.

X509Certificate2 cert = new X509Certificate2("c:\\myCert.pfx", "test", X509KeyStorageFlags.Exportable);

File.WriteAllBytes("c:\\testcer.cer", cert.Export(X509ContentType.Cert));

I tried removing the 'X509KeyStorageFlags.Exportable" but that doesn't work. Am I missing something?

Edit - I tried

File.WriteAllText("c:\\testcer.cer",Convert.ToBase64String(cert.Export(X509ContentType.Cert)))

and that seems to work, however, missing the "-----BEGIN CERTIFICATE-----" and "-----END CERTIFICATE-----"

Answer 1

Perhaps

/// <summary>
/// Export a certificate to a PEM format string
/// </summary>
/// <param name="cert">The certificate to export</param>
/// <returns>A PEM encoded string</returns>
public static string ExportToPEM(X509Certificate cert)
{
    StringBuilder builder = new StringBuilder();            

    builder.AppendLine("-----BEGIN CERTIFICATE-----");
    builder.AppendLine(Convert.ToBase64String(cert.Export(X509ContentType.Cert), Base64FormattingOptions.InsertLineBreaks));
    builder.AppendLine("-----END CERTIFICATE-----");

    return builder.ToString();
}

Answer 2

try this:

X509Certificate2 cerifikata = new X509Certificate2("C://certificate.pfx");
File.WriteAllBytes("D://Test.cer",cerifikata.Export(X509ContentType.Cert));

Answer 3

For those implementing something similar in .NET Core, here's the code, based on what tyranid did. Base64FormattingOptions.InsertLineBreaks doesn't exist in .NET Core, so I had to implement my own way to do line breaking.

    // Certificates content has 64 characters per lines
    private const int MaxCharactersPerLine = 64;

    /// <summary>
    /// Export a certificate to a PEM format string
    /// </summary>
    /// <param name="cert">The certificate to export</param>
    /// <returns>A PEM encoded string</returns>
    public static string ExportToPem(this X509Certificate2 cert)
    {
        var builder = new StringBuilder();
        var certContentBase64 = Convert.ToBase64String(cert.Export(X509ContentType.Cert));
        // Calculates the max number of lines this certificate will take.
        var certMaxNbrLines = Math.Ceiling((double)certContentBase64.Length / MaxCharactersPerLine);

        builder.AppendLine("-----BEGIN CERTIFICATE-----");
        for (var index = 0; index < certMaxNbrLines; index++)
        {
            var maxSubstringLength = index * MaxCharactersPerLine + MaxCharactersPerLine > certContentBase64.Length
                ? certContentBase64.Length - index * MaxCharactersPerLine
                : MaxCharactersPerLine;
            builder.AppendLine(certContentBase64.Substring(index * MaxCharactersPerLine, maxSubstringLength));
        }
        builder.AppendLine("-----END CERTIFICATE-----");

        return builder.ToString();
    }

Answer 4

//however, missing the "-----BEGIN CERTIFICATE-----" and "-----END CERTIFICATE-----"

These missing lines are optional. CA may generate them or not depending on settings. For all practical reasons they can be removed from the Base64 encoded file.