How to decrypt a SAML Response in .NET

I have SAML Response and Metadata URL provided by Client (Identity Provider). How I (Service Provider) Can decrypt the SAML Response

Below is the SAML Response

<samlp:Response ID="_17222aef-2970-44d1-aae6-1c25187c4319" Version="2.0" IssueInstant="2017-06-29T10:23:12.036Z" Destination="https://ssotest-1246771484.ap-south-1.elb.amazonaws.com/ssotest/index.html" Consent="urn:oasis:names:tc:SAML:2.0:consent:unspecified"
  InResponseTo="a351b3fi19a2024838868e374da59j6" xmlns:samlp="urn:oasis:names:tc:SAML:2.0:protocol">
  <Issuer xmlns="urn:oasis:names:tc:SAML:2.0:assertion">https://yyy.xxx.com/adfs/zzz/trust</Issuer>
  <samlp:Status>
    <samlp:StatusCode Value="urn:oasis:names:tc:SAML:2.0:status:Success" />
  </samlp:Status>
  <EncryptedAssertion xmlns="urn:oasis:names:tc:SAML:2.0:assertion">
    <xenc:EncryptedData Type="http://www.w3.org/2001/04/xmlenc#Element" xmlns:xenc="http://www.w3.org/2001/04/xmlenc#">
      <xenc:EncryptionMethod Algorithm="http://www.w3.org/2001/04/xmlenc#aes256-cbc" />
      <KeyInfo xmlns="http://www.w3.org/2000/09/xmldsig#">
        <e:EncryptedKey xmlns:e="http://www.w3.org/2001/04/xmlenc#">
          <e:EncryptionMethod Algorithm="http://www.w3.org/2001/04/xmlenc#rsa-oaep-mgf1p">
            <DigestMethod Algorithm="http://www.w3.org/2000/09/xmldsig#sha1" />
          </e:EncryptionMethod>
          <KeyInfo>
        <ds:X509Data xmlns:ds="http://www.w3.org/2000/09/xmldsig#">
          <ds:X509IssuerSerial>
            <ds:X509IssuerName>CN=apollo, OU=R&amp;D, O=RM5 Software Oy, L=Helsinki, S=Uusimaa, C=FI</ds:X509IssuerName>
            <ds:X509SerialNumber>1357039681</ds:X509SerialNumber>
          </ds:X509IssuerSerial>
        </ds:X509Data>
      </KeyInfo>
      <e:CipherData>
        <e:CipherValue>f6yX7d1FF4eHtj79WRxJ/xga3qhUASk79sTHWDfKW/bHbIGL+UVwBIdQIh21AMbLN/1cgiVCps7UBAoaipew7JQCq1EYQR/ipFO7Wcmoqs5V1h/KwBgNdhT/L/TqAacIz9QoRPkNhxsDAKMvdj9wwPZhYHGvqC1cFgrMZjMS4r1VlF2qh2TgQVgv9PjA234dZfNLTUmu1WNRjs30mtcZAZtnwB8A6sUwQsJCSfKfXoTcEAYrD2Am+9FQdHBnrZ3HwtH1gkbe0pAYtEPqX+yzRm7wtsMLj9F4+PoE1Ax3Ju3kpPiV5u1au1CCJG8CzuxbswFII4npKlwjuKm9y7A8YA==</e:CipherValue>
      </e:CipherData>
    </e:EncryptedKey>
  </KeyInfo>
  <xenc:CipherData>
    <xenc:CipherValue>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</xenc:CipherValue>
  </xenc:CipherData>
</xenc:EncryptedData>

How encryption scenario works in SAML: identity provider encrypts some elements of the SAML response with service provider's public key. The service provider decrypts using the private key that corresponds to the public key used to encrypt. In other words, the service provider needs to own a keypair - private key and public key - for this use case to work.

Assuming you have the private key for decryption, you just need to decide on the implementation approach. Rolling your own is technically possible but unlikely to succeed. For .NET we recommend either Sustainsys or ITFoxtec, both are OSS and support decryption.