ECDsaCertificateExtensions.cs

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using Internal.Cryptography;
using Internal.Cryptography.Pal;
 
namespace System.Security.Cryptography.X509Certificates;
 
public static class ECDsaCertificateExtensions
{
    public static ECDsa? GetECDsaPublicKey(this X509Certificate2 certificate)
    {
        return certificate.GetPublicKey<ECDsa>((X509Certificate2 cert) => HasECDsaKeyUsage(cert));
    }
 
    public static ECDsa? GetECDsaPrivateKey(this X509Certificate2 certificate)
    {
        return certificate.GetPrivateKey<ECDsa>((X509Certificate2 cert) => HasECDsaKeyUsage(cert));
    }
 
    public static X509Certificate2 CopyWithPrivateKey(this X509Certificate2 certificate, ECDsa privateKey)
    {
        if (certificate == null)
        {
            throw new ArgumentNullException("certificate");
        }
        if (privateKey == null)
        {
            throw new ArgumentNullException("privateKey");
        }
        if (certificate.HasPrivateKey)
        {
            throw new InvalidOperationException(System.SR.Cryptography_Cert_AlreadyHasPrivateKey);
        }
        using (ECDsa eCDsa = certificate.GetECDsaPublicKey())
        {
            if (eCDsa == null)
            {
                throw new ArgumentException(System.SR.Cryptography_PrivateKey_WrongAlgorithm);
            }
            if (!Internal.Cryptography.Helpers.AreSamePublicECParameters(eCDsa.ExportParameters(includePrivateParameters: false), privateKey.ExportParameters(includePrivateParameters: false)))
            {
                throw new ArgumentException(System.SR.Cryptography_PrivateKey_DoesNotMatch, "privateKey");
            }
        }
        ICertificatePal pal = certificate.Pal.CopyWithPrivateKey(privateKey);
        return new X509Certificate2(pal);
    }
 
    private static bool HasECDsaKeyUsage(X509Certificate2 certificate)
    {
        foreach (X509Extension extension in certificate.Extensions)
        {
            if (extension.Oid.Value == "2.5.29.15")
            {
                X509KeyUsageExtension x509KeyUsageExtension = (X509KeyUsageExtension)extension;
                if ((x509KeyUsageExtension.KeyUsages & X509KeyUsageFlags.KeyAgreement) == 0)
                {
                    return true;
                }
                return (x509KeyUsageExtension.KeyUsages & (X509KeyUsageFlags.CrlSign | X509KeyUsageFlags.KeyCertSign | X509KeyUsageFlags.NonRepudiation | X509KeyUsageFlags.DigitalSignature)) != 0;
            }
        }
        return true;
    }
}