Reading XML Digital Signature value

For a project I’m working on, I have to read in an XML digital signature – XmlDSig. In this post, I’m going to show how to read an XmlDsig value using SignedXml object from namespace System.Security.Cryptography.Xml.

I add a class to hold my signature data

    public class SignedObjectModel
    {
        public X509Certificate2 Certificate { get; set; }
        public DigestModel Digest { get; set; }
        public SignatureModel Signature { get; set; }
    }

    public class DigestModel
    {
        public string Value { get; set; }
        public string Encoding { get; set; }
        public string Algorithm { get; set; }
    }

    public class SignatureModel
    {
        public string Value { get; set; }
        public string Algorithm { get; set; }
        public string Encoding { get; set; }
    }

The following is the function to read the XmlDsig value

        public SignedObjectModel ReadXmlDSigValue(string value)
        {
            var xmlDoc = new XmlDocument();
            xmlDoc.LoadXml(value);
            XmlNodeList nodeList = xmlDoc.GetElementsByTagName("Signature", SignedXml.XmlDsigNamespaceUrl);
            SignedXml signedXml = new SignedXml((XmlElement)nodeList[0]);
            signedXml.LoadXml((XmlElement)nodeList[0]);

            var certValue = xmlDoc.GetElementsByTagName("X509Certificate")[0].InnerText;

            var cert = new X509Certificate2(Convert.FromBase64String(certValue));

            var checkSignature = signedXml.CheckSignature(cert, true);
            return new SignedObjectModel
            {
                Certificate = cert,
                Digest = new DigestModel
                {
                    Value = xmlDoc.GetElementsByTagName("DigestValue")[0].InnerText,
                    Encoding = "Base64",
                    Algorithm = (signedXml.SignedInfo.References[0] as Reference).DigestMethod
                },
                Signature = new SignatureModel
                {
                    Value = xmlDoc.GetElementsByTagName("SignatureValue")[0].InnerText,
                    Algorithm = signedXml.SignatureMethod,
                    Encoding = "Base64"
                }
            };
        }