(Swift 3,4,5...) Decrypt a SAML Response

Demonstrates how to decrypt a SAML response.

Note: This example requires Chilkat v9.5.0.76 or greater.

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func chilkatTest() {
    // This example requires the Chilkat API to have been previously unlocked.
    // See Global Unlock Sample for sample code.

    // This example decrypts this SAML response:

    // <?xml version="1.0" encoding="UTF-8" ?>
    // <saml2p:Response Destination="https://deskflow-asp2.com/ubc/ubcdfe.dll/cwlacs" ID="_e4585eaeedbcaf7c24dff7f1ee2499f5" IssueInstant="2018-10-11T17:46:20.727Z" Version="2.0" xmlns:saml2p="urn:oasis:names:tc:SAML:2.0:protocol">
    //     <saml2:Issuer xmlns:saml2="urn:oasis:names:tc:SAML:2.0:assertion">https://authentication.stg.id.ubc.ca</saml2:Issuer>
    //     <ds:Signature xmlns:ds="http://www.w3.org/2000/09/xmldsig#">
    //         <ds:SignedInfo>
    //             <ds:CanonicalizationMethod Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#"/>
    //             <ds:SignatureMethod Algorithm="http://www.w3.org/2001/04/xmldsig-more#rsa-sha256"/>
    //             <ds:Reference URI="#_e4585eaeedbcaf7c24dff7f1ee2499f5">
    //                 <ds:Transforms>
    //                     <ds:Transform Algorithm="http://www.w3.org/2000/09/xmldsig#enveloped-signature"/>
    //                     <ds:Transform Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#"/>
    //                 </ds:Transforms>
    //                 <ds:DigestMethod Algorithm="http://www.w3.org/2001/04/xmlenc#sha256"/>
    //                 <ds:DigestValue>1ui22tqFyYEOoWI19CMwz4n+ynxNjLDGdTeRMdi60EU=</ds:DigestValue>
    //             </ds:Reference>
    //         </ds:SignedInfo>
    //         <ds:SignatureValue>ROg7FXV6vsp8socVhdo76/i7cRHGGKIveAiScKdujZT0QrHVqIvvbZ/RnwvEMJ9H9i/kJFAQA171
    // 		Eo2kDjSdvNFQ/YcKaJUwMtAwT05yVatGV42RZKEf7ME+vpcCTR1LWZdrhat1FWCg1MNQwNWB0EL5
    // 		fEP2a4jAcSTB8tFbjTAHsv7IWC39E5RVv99mACYXLa7iGZLtORANZxgYu5qQgmH6pUkI6Z1cpmf+
    // 		m9mIjKM6LF0EvLfWOBWL6udZ+GsHPOLjVTJg+1S0xb9FQCYDVW1QhbjSS0icKHKTNNbrsaxllVDY
    // 		m4q27YQjRh+XxugPgvsZ61Pxlto8Jbg+6jUlMQ==</ds:SignatureValue>
    //         <ds:KeyInfo>
    //             <ds:X509Data>
    //                 <ds:X509Certificate>MIIDTTCCAjWgAwIBAgIVAJccYyIV6wly8XyddumpgnHMJ2JLMA0GCSqGSIb3DQEBCwUAMCcxJTAj
    // 			BgNVBAMMHGF1dGhlbnRpY2F0aW9uLnN0Zy5pZC51YmMuY2EwHhcNMTcwMzAxMTk1NDM0WhcNMzcw
    // 			...
    // 			xUuh6HuHKIwQqHBz7udxbH3Zbb6jXGDJjiDHt1LRJ8xbVisFIcDlIwsGQQi0HeEJfx4P</ds:X509Certificate>
    //             </ds:X509Data>
    //         </ds:KeyInfo>
    //     </ds:Signature>
    //     <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 Id="_314d80b9cf02d8eda8d686a6ffd626cf" 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#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="_d7b6da6fb59a627ebb4a96928441ab79" Recipient="https://ubcdfe.deskflow-asp2.com" 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>MIICuzCCAiQCCQD3bpigRnKMSzANBgkqhkiG9w0BAQsFADCBoTELMAkGA1UEBhMCQ0ExEDAOBgNV
    // 				BAgMB09udGFyaW8xEDAOBgNVBAcMB1Rvcm9udG8xJjAkBgNVBAoMHVRhY3RpY2FsIEJ1c2luZXNz
    // 				...
    // 				kVRcHd1UK3q7G8FoykWjdQz/0EoMTfEZ+Md56mLOe48eMUZV2ONZuL1kDCEKw1UwkaDQI4Pf8pzx
    // 				82b9rgw9wBDtvu5eFPlUGEGIBw==</ds:X509Certificate>
    //                         </ds:X509Data>
    //                     </ds:KeyInfo>
    //                     <xenc:CipherData xmlns:xenc="http://www.w3.org/2001/04/xmlenc#">
    //                         <xenc:CipherValue>BNHfUOpgdPE5BgpN2VIZIDthMAv1rxk91qVnWyCZOG9bmUKChJtTUqMpndot7VJwYuyKFshkAdnT
    // 				D79KGdlSA1xHKcVeZXXzDWglqSyYjzhDCsyOhPaI4HelMFgCLwyFz89uEpUpqlvfl8ol3Am/XnzQ
    // 				Vp7V7oS76hocjUI51Qs=</xenc:CipherValue>
    //                     </xenc:CipherData>
    //                 </xenc:EncryptedKey>
    //             </ds:KeyInfo>
    //             <xenc:CipherData xmlns:xenc="http://www.w3.org/2001/04/xmlenc#">
    //                 <xenc:CipherValue>R6l7tmbnXrOfBgB8lA3KnwLYsLH5ZO5omQ7Hp5K05atzw2o55xmCXVMYhNneFxMtxUh6raEyHeZX
    // 			PTZNgWrvdqc4GYND/R7MhRrJzk9OAq1WyoOXwbtRpwNDwWA4N2IuprPQJbvjVxaw/PesZMZwZqlp
    // 			...
    // 			zm9zAxahyu8Ooe8M4r3HN2cY0JxxxkZtDiulbnyA+rRtXfBRJtangvFQ4iFAnzM/Yg9hMyW9jcu0
    // 			S7FzuRB9ONMxi+nh0IFWgqp+</xenc:CipherValue>
    //             </xenc:CipherData>
    //         </xenc:EncryptedData>
    //     </saml2:EncryptedAssertion>
    // </saml2p:Response>

    // The sample encrypted SAML response and RSA private key are available online:
    let http = CkoHttp()!
    let sbSamlResponse = CkoStringBuilder()!
    let sbPrivateKeyPem = CkoStringBuilder()!
    var success: Bool = http.quickGetSb("https://chilkatdownload.com/data/samlresponse.xml", sbContent: sbSamlResponse)
    if success == true {
        success = http.quickGetSb("https://chilkatdownload.com/data/samlresponse_privkey.pem", sbContent: sbPrivateKeyPem)
    }

    if success != true {
        print("\(http.lastErrorText!)")
        return
    }

    let xml = CkoXml()!
    xml.loadSb(sbSamlResponse, autoTrim: true)

    // Load the RSA private key..
    let privkey = CkoPrivateKey()!
    success = privkey.loadPem(sbPrivateKeyPem.getAsString())
    if success != true {
        print("\(privkey.lastErrorText!)")
        return
    }

    // Prepare an RSA object w/ the private key...
    let rsa = CkoRsa()!
    success = rsa.importPrivateKeyObj(privkey)
    if success != true {
        print("\(rsa.lastErrorText!)")
        return
    }

    // RSA will be used to decrypt the xenc:EncryptedKey
    // The bytes to be decrypted are in xenc:CipherValue (in base64 format)
    var encryptedAesKey: String? = xml.getChildContent("saml2:EncryptedAssertion|xenc:EncryptedData|ds:KeyInfo|xenc:EncryptedKey|xenc:CipherData|xenc:CipherValue")
    if xml.lastMethodSuccess != true {
        print("Encrypted AES key not found.")
        return
    }

    print("Encrypted AES key (base64) = \(encryptedAesKey!)")

    let bdAesKey = CkoBinData()!
    bdAesKey.appendEncoded(encryptedAesKey, encoding: "base64")

    let sbRsaAlg = CkoStringBuilder()!
    sbRsaAlg.append(xml.chilkatPath("saml2:EncryptedAssertion|xenc:EncryptedData|ds:KeyInfo|xenc:EncryptedKey|xenc:EncryptionMethod|(Algorithm)"))
    print("sbRsaAlg contains: \(sbRsaAlg.getAsString()!)")
    if sbRsaAlg.contains("rsa-oaep", caseSensitive: true) == true {
        rsa.oaepPadding = true
    }

    // Note: The DecryptBd method is introduced in Chilkat v9.5.0.76
    success = rsa.decryptBd(bdAesKey, usePrivateKey: true)
    if success != true {
        print("\(rsa.lastErrorText!)")
        return
    }

    print("Decrypted AES key (hex) = \(bdAesKey.getEncoded("hex")!)")

    // Get the encrypted XML (in base64) to be decrypted w/ the AES key.
    var encrypted64: String? = xml.getChildContent("saml2:EncryptedAssertion|xenc:EncryptedData|xenc:CipherData|xenc:CipherValue")
    if xml.lastMethodSuccess != true {
        print("Encrypted data not found.")
        return
    }

    let bdEncrypted = CkoBinData()!
    bdEncrypted.appendEncoded(encrypted64, encoding: "base64")

    // Get the symmetric algorithm:  "http://www.w3.org/2001/04/xmlenc#aes128-cbc"
    // and set the symmetric decrypt properties.
    let crypt = CkoCrypt2()!
    let sbAlg = CkoStringBuilder()!
    sbAlg.append(xml.chilkatPath("saml2:EncryptedAssertion|xenc:EncryptedData|xenc:EncryptionMethod|(Algorithm)"))
    if sbAlg.contains("aes128-cbc", caseSensitive: true) == true {
        crypt.cryptAlgorithm = "aes"
        crypt.keyLength = 128
        crypt.cipherMode = "cbc"
        // The 1st 16 bytes of the encrypted data are the AES IV.
        crypt.setEncodedIV(bdEncrypted.getEncodedChunk(0, numBytes: 16, encoding: "hex"), encoding: "hex")
        bdEncrypted.removeChunk(0, numBytes: 16)
    }

    // Other algorithms, key lengths, etc, can be supported by checking for different Algorithm attribute values..

    crypt.setEncodedKey(bdAesKey.getEncoded("hex"), encoding: "hex")

    // AES decrypt...
    success = crypt.decryptBd(bdEncrypted)
    if success != true {
        print("\(crypt.lastErrorText!)")
        return
    }

    // Get the decrypted XML
    var decryptedXml: String? = bdEncrypted.getString("utf-8")
    print("Decrypted XML:")
    print("\(decryptedXml!)")

    // The decrypted XML looks like this:

    // <saml2:Assertion xmlns:saml2="urn:oasis:names:tc:SAML:2.0:assertion" ID="_226e565c548db7986d165d7d969b48b4" IssueInstant="2018-10-11T17:46:20.727Z" Version="2.0">
    // ...
    // ...
    // ...
    // </saml2:Assertion>

    let xmlAssertion = CkoXml()!
    xmlAssertion.load(decryptedXml)

    // Replace the saml2:EncryptedAssertion XML subtree with the saml2:Assertion XML.
    var xmlEncryptedAssertion: CkoXml? = xml.findChild("saml2:EncryptedAssertion")
    xmlEncryptedAssertion!.swapTree(xmlAssertion)
    xmlEncryptedAssertion = nil

    // The decrypted XML assertion has now replaced the encrypted XML assertion.
    // Examine the fully decrypted XML document:
    print("Full XML SAML document with decrypted assertion:")
    print("\(xml.getXml()!)")

}