无法使用 xml (X509Certificate2) 中提供的证书公钥验证签名值

>我花了100多个小时研究这个主题，其他编写原始项目的高级程序员也无法使其工作。我有一个带有签名值、证书 （X509Certificate2） 和摘要值参数的 xml。在同一 xml 中声明的创建和给定的签名值是通过将串联字段（等于摘要值）转换为哈希 （SHA1），然后通过私钥加密来实现的。为了隐私起见，私钥已从证书中取出，我只有公钥。现在，无论我如何编码，我总是得到一个错误的值（如VerifyHash/verifyHashResult is false）。这是我正在使用的代码：

请帮忙。

 static void VerifyHash(string sigVal , string digestVal, System.Security.Cryptography.X509Certificates.X509Certificate2 cert)
        {
            sigValInBytes = Convert.FromBase64String(sigVal);
            try
            {
 using (RSACryptoServiceProvider rsaProviderDecrypt = (RSACryptoServiceProvider)cert.PublicKey.Key)
               {
// Line below always return value of FALSE no matter how I code it. Here I want to verify the hashed freshly calculated digest value that is now hashed with the signature value
                    rsaProviderDecrypt.Decrypt(sigValInBytes, false);
                   rsaProviderDecrypt.Dispose();
               }
             }
        }

// At the main program I get the certificate from the xml given and call the method above:
main
{
// Code below gets the certificate details from a given xml, details of each variable confirmed to be accurate.
char[] Base64_x509ByteArray;
Base64_x509ByteArray = t.DigitalSignatures.First().X509Data.ToCharArray();
byte[] x509ByteArray;
x509ByteArray = Convert.FromBase64CharArray(Base64_x509ByteArray, 0, Base64_x509ByteArray.Length);
// Here am creating the certificate from the gathered data/certificate:
System.Security.Cryptography.X509Certificates.X509Certificate2 cert = new System.Security.Cryptography.X509Certificates.X509Certificate2(x509ByteArray);
VerifyHash(t.DigitalSignatures.FirstOrDefault().SignatureValue.Trim(), concatenatedFieldValues, cert);
}