<?xml version="1.0" encoding="UTF-8"?>
<saml2p:Response xmlns:saml2p="urn:oasis:names:tc:SAML:2.0:protocol" Destination="https://cct.bananaqa.net/SignIn/SamlAcs" ID="_584d6720576184d6a6f7c396f850b019" InResponseTo="Banana_7a26613a-b24e-461c-af39-b5ea8e11be89" IssueInstant="2016-04-13T18:10:00.709Z" Version="2.0">
    <saml2:Issuer xmlns:saml2="urn:oasis:names:tc:SAML:2.0:assertion" Format="urn:oasis:names:tc:SAML:2.0:nameid-format:entity">https://scb1.cct.edu/idp/shibboleth</saml2:Issuer>
    <saml2p:Status>
        <saml2p:StatusCode Value="urn:oasis:names:tc:SAML:2.0:status:Success" /></saml2p:Status>
    <saml2:EncryptedAssertion xmlns:saml2="urn:oasis:names:tc:SAML:2.0:assertion">
        <xenc:EncryptedData xmlns:xenc="http://www.w3.org/2001/04/xmlenc#" Id="_4cd6916c8c1adc98c371a202c6c50f4f" Type="http://www.w3.org/2001/04/xmlenc#Element">
            <xenc:EncryptionMethod Algorithm="http://www.w3.org/2001/04/xmlenc#aes128-cbc" xmlns:xenc="http://www.w3.org/2001/04/xmlenc#" />
            <ds:KeyInfo xmlns:ds="http://www.w3.org/2000/09/xmldsig#">
                <xenc:EncryptedKey Id="_aa1cb5932dd3ed1a5d968e09f41c79e8" xmlns:xenc="http://www.w3.org/2001/04/xmlenc#">
                    <xenc:EncryptionMethod Algorithm="http://www.w3.org/2001/04/xmlenc#rsa-oaep-mgf1p" xmlns:xenc="http://www.w3.org/2001/04/xmlenc#">
                        <ds:DigestMethod Algorithm="http://www.w3.org/2000/09/xmldsig#sha1" xmlns:ds="http://www.w3.org/2000/09/xmldsig#" />
                    </xenc:EncryptionMethod>
                    <ds:KeyInfo>
                        <ds:X509Data>
                            <ds:X509Certificate>MIIFODCCBCCgAwIBAgIJAOqAYZiaSD9SMA0GCSqGSIb3DQEBCwUAMIG0MQswCQYDVQQGEwJVUzEQMA4GA1UECBMHQXJpem9uYTETMBEGA1UEBxMKU2.......BgwFoAUQMK9J47MNIMwojPX+2yz8LQsgM4wMwYDVR0RBCwwKoIUKi5hd2FyZHNwcmluZy1xYS5uZXSCEmF3YXJkc3ByaW5nLXFhLm5ldDAdBgNVHQ4EFgQUADqtjmhLN8HW6DDSOJ5PE2UVNKgwDQY.......Eh6G+GMByWVvSi80WXqnzV2oGTthFx3a2hyT3ndcr9RL17GE7wT5nw=</ds:X509Certificate>
                        </ds:X509Data>
                    </ds:KeyInfo>
                    <xenc:CipherData xmlns:xenc="http://www.w3.org/2001/04/xmlenc#">
                        <xenc:CipherValue>......w8QEZG0qI/asmzbIDcP4ahkfeKQ96pUDg7xTtcPhKseRlOxUW7alwe2PHVYP9O0bWWxz/4Ih6kvl2cVPDql6QRpJAimmdY...==</xenc:CipherValue>
                    </xenc:CipherData>
                </xenc:EncryptedKey>
            </ds:KeyInfo>
            <xenc:CipherData xmlns:xenc="http://www.w3.org/2001/04/xmlenc#">
                <xenc:CipherValue>.........SEGgqL4Kxr/Ddon78edBK4tSLUyLS12bmYHKQQRCauL9kuIskAQJdx8dMEW0dKC+r+n445Gc5k2fGuvIReIKRU4SgUloWhqme29SYC3La5t1k9QvGFuh7qc1/KrH/UAdtA47NfnxE4ZXdjTmAAwxrf41ARHFCEb5it9F8zvv21vfkACExYVQFY8Kgcww2augZldehH/Ycx4IdDVgGQmLz46HGrHfFM3y9Yy1GET1jELQ/R/HLc35KbFdzHa8fxKB4/boS+Yp2e6Sme62FCVJkSljP1XOGhfX/K+p6X67YR9Atyqova4UqNP+8Fv8qAlPM5kQC75WqKI2LtpjvngTG5MjqCUphZM/wKFKWFjH8D5YatK31xIcG9hqdxpDcq3Eh84tRPWKG+WF2Rl3kmjCy1XvyTPhcAqGna/BRtqcrtFrDY4GyOAJTtj.......</xenc:CipherValue>
            </xenc:CipherData>
        </xenc:EncryptedData>
    </saml2:EncryptedAssertion>
</saml2p:Response>

using System;
using System.IO;
using System.Linq;
using System.Security.Cryptography;
using System.Security.Cryptography.X509Certificates;
using System.Security.Cryptography.Xml;
using System.Text;
using System.Xml;

namespace Service.SSO
{
public class Saml2DecryptResponse
{
    private XmlNamespaceManager _nsManager;
    private XmlDocument _xmlDoc;

    public Saml2DecryptResponse(XmlDocument xmlDocument)
    {
        _xmlDoc = xmlDocument;

        _nsManager = new XmlNamespaceManager(_xmlDoc.NameTable);
        _nsManager.AddNamespace("ds", "http://www.w3.org/2000/09/xmldsig#");
        _nsManager.AddNamespace("saml", "urn:oasis:names:tc:SAML:2.0:assertion");
        _nsManager.AddNamespace("samlp", "urn:oasis:names:tc:SAML:2.0:protocol");
        _nsManager.AddNamespace("xenc", "http://www.w3.org/2001/04/xmlenc#");
    }

    public XmlNode GetDecryptedAssertion(X509Certificate2 myCert)
    {
        RSACryptoServiceProvider privateCsp = (RSACryptoServiceProvider)myCert.PrivateKey;

        // load the xmlDoc
        EncryptedXml encXml = new EncryptedXml(_xmlDoc);
        XmlElement encryptedDataElement = _xmlDoc.GetElementsByTagName("xenc:EncryptedData")[0] as XmlElement;
        EncryptedData encryptedData = new EncryptedData();
        encryptedData.LoadXml(encryptedDataElement);

        //get your cipher data from the encrypted assertion key info
        byte[] cipherBytes = GetKeyCipherValue();

        // use the RSACryptoServiceProvider to decrypt it
        var symKey = privateCsp.Decrypt(cipherBytes, true);

        // get the assertion data
        byte[] dataCipherBytes = GetEncryptedAssertionData();

        // and the encryption method
        string encMethod = GetEncryptionMethod();

        // build your symmetric algorythm, used to decrypt your assertion data
        SymmetricAlgorithm symAlg = null;
        symAlg = GetAlgorithm(encMethod);
        symAlg.IV = encXml.GetDecryptionIV(encryptedData, encMethod);

        // decrypt the assertion data
        byte[] decryptedAssertionData = DecryptBytes(symAlg, dataCipherBytes, symKey, symAlg.IV);
        string rawText = Encoding.UTF8.GetString(decryptedAssertionData);

        // clean up the unencrypted text
        int samlStart = rawText.IndexOf("<saml:Assertion");
        int samlEnd = rawText.IndexOf("</saml:Assertion>") + 17 - samlStart;
        string cleanText = rawText.Substring(samlStart, samlEnd);

        // turn it into an xml element and return it
        XmlDocumentFragment fragment = _xmlDoc.CreateDocumentFragment();
        fragment.InnerXml = cleanText;
        return fragment;
    }

    public static byte[] DecryptBytes(SymmetricAlgorithm algorithm, byte[] encryptedData, byte[] keyBytes, byte[] iv)
    {
        byte[] plainTextBytes;

        int decryptedBytesCount;

        using (var decryptor = algorithm.CreateDecryptor(keyBytes, iv))
        {
            using (var memoryStream = new MemoryStream(encryptedData))
            {
                using (var cryptoStream = new CryptoStream(memoryStream, decryptor, CryptoStreamMode.Read))
                {
                    plainTextBytes = new byte[encryptedData.Length];
                    decryptedBytesCount = cryptoStream.Read(plainTextBytes, 0, plainTextBytes.Length);

                    memoryStream.Close();
                    cryptoStream.Close();
                }
            }
        }

        return plainTextBytes;
    }

    public byte[] GetKeyCipherValue()
    {
        var node = GetNode("//xenc:EncryptedKey//xenc:CipherData//xenc:CipherValue");
        return Convert.FromBase64String(node.InnerText);
    }

    public byte[] GetEncryptedAssertionData()
    {
        var node = GetNode("//xenc:EncryptedData//xenc:CipherData//xenc:CipherValue");
        return Convert.FromBase64String(node.InnerText);
    }

    public string GetEncryptionMethod()
    {
        XmlNode node = GetNode("//xenc:EncryptionMethod");
        return node.Attributes["Algorithm"].Value.Trim();
    }

    public XmlNode GetNode(string xpath)
    {
        return _xmlDoc.SelectSingleNode(xpath, _nsManager);
    }

    private static SymmetricAlgorithm GetAlgorithm(string symAlgUri)
    {
        SymmetricAlgorithm symAlg = null;

        switch (symAlgUri)
        {
            case EncryptedXml.XmlEncAES128Url:
            case EncryptedXml.XmlEncAES128KeyWrapUrl:
                symAlg = SymmetricAlgorithm.Create("Rijndael");
                symAlg.KeySize = 128;
                symAlg.Padding = PaddingMode.None;
                break;
            case EncryptedXml.XmlEncAES192Url:
            case EncryptedXml.XmlEncAES192KeyWrapUrl:
                symAlg = SymmetricAlgorithm.Create("Rijndael");
                symAlg.KeySize = 192;
                break;
            case EncryptedXml.XmlEncAES256Url:
            case EncryptedXml.XmlEncAES256KeyWrapUrl:
                symAlg = SymmetricAlgorithm.Create("Rijndael");
                symAlg.KeySize = 256;
                break;
            case EncryptedXml.XmlEncDESUrl:
                symAlg = SymmetricAlgorithm.Create("DES");
                break;
            case EncryptedXml.XmlEncTripleDESUrl:
            case EncryptedXml.XmlEncTripleDESKeyWrapUrl:
                symAlg = SymmetricAlgorithm.Create("TripleDES");
                break;
            default:
                throw new ArgumentException("symAlgUri");
        }

        return symAlg;
    }
}
}