(Ruby) Decrypt a SAML Response

Demonstrates how to decrypt a SAML response.

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

Chilkat Ruby Downloads install from rubygems.org gem install chilkat or download... Ruby Library for Windows, MacOS, Linux, Alpine Linux

require 'chilkat'

#  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:
http = Chilkat::CkHttp.new()
sbSamlResponse = Chilkat::CkStringBuilder.new()
sbPrivateKeyPem = Chilkat::CkStringBuilder.new()
success = http.QuickGetSb("https://chilkatdownload.com/data/samlresponse.xml",sbSamlResponse)
if (success == true)
    success = http.QuickGetSb("https://chilkatdownload.com/data/samlresponse_privkey.pem",sbPrivateKeyPem)
end

if (success != true)
    print http.lastErrorText() + "\n";
    exit
end

xml = Chilkat::CkXml.new()
xml.LoadSb(sbSamlResponse,true)

#  Load the RSA private key..
privkey = Chilkat::CkPrivateKey.new()
success = privkey.LoadPem(sbPrivateKeyPem.getAsString())
if (success != true)
    print privkey.lastErrorText() + "\n";
    exit
end

#  Prepare an RSA object w/ the private key...
rsa = Chilkat::CkRsa.new()
success = rsa.ImportPrivateKeyObj(privkey)
if (success != true)
    print rsa.lastErrorText() + "\n";
    exit
end

#  RSA will be used to decrypt the xenc:EncryptedKey
#  The bytes to be decrypted are in xenc:CipherValue (in base64 format)
encryptedAesKey = xml.getChildContent("saml2:EncryptedAssertion|xenc:EncryptedData|ds:KeyInfo|xenc:EncryptedKey|xenc:CipherData|xenc:CipherValue")
if (xml.get_LastMethodSuccess() != true)
    print "Encrypted AES key not found." + "\n";
    exit
end

print "Encrypted AES key (base64) = " + encryptedAesKey + "\n";

bdAesKey = Chilkat::CkBinData.new()
bdAesKey.AppendEncoded(encryptedAesKey,"base64")

sbRsaAlg = Chilkat::CkStringBuilder.new()
sbRsaAlg.Append(xml.chilkatPath("saml2:EncryptedAssertion|xenc:EncryptedData|ds:KeyInfo|xenc:EncryptedKey|xenc:EncryptionMethod|(Algorithm)"))
print "sbRsaAlg contains: " + sbRsaAlg.getAsString() + "\n";
if (sbRsaAlg.Contains("rsa-oaep",true) == true)
    rsa.put_OaepPadding(true)
end

#  Note: The DecryptBd method is introduced in Chilkat v9.5.0.76
success = rsa.DecryptBd(bdAesKey,true)
if (success != true)
    print rsa.lastErrorText() + "\n";
    exit
end

print "Decrypted AES key (hex) = " + bdAesKey.getEncoded("hex") + "\n";

#  Get the encrypted XML (in base64) to be decrypted w/ the AES key.
encrypted64 = xml.getChildContent("saml2:EncryptedAssertion|xenc:EncryptedData|xenc:CipherData|xenc:CipherValue")
if (xml.get_LastMethodSuccess() != true)
    print "Encrypted data not found." + "\n";
    exit
end

bdEncrypted = Chilkat::CkBinData.new()
bdEncrypted.AppendEncoded(encrypted64,"base64")

#  Get the symmetric algorithm:  "http://www.w3.org/2001/04/xmlenc#aes128-cbc"
#  and set the symmetric decrypt properties.
crypt = Chilkat::CkCrypt2.new()
sbAlg = Chilkat::CkStringBuilder.new()
sbAlg.Append(xml.chilkatPath("saml2:EncryptedAssertion|xenc:EncryptedData|xenc:EncryptionMethod|(Algorithm)"))
if (sbAlg.Contains("aes128-cbc",true) == true)
    crypt.put_CryptAlgorithm("aes")
    crypt.put_KeyLength(128)
    crypt.put_CipherMode("cbc")
    #  The 1st 16 bytes of the encrypted data are the AES IV.
    crypt.SetEncodedIV(bdEncrypted.getEncodedChunk(0,16,"hex"),"hex")
    bdEncrypted.RemoveChunk(0,16)
end

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

crypt.SetEncodedKey(bdAesKey.getEncoded("hex"),"hex")

#  AES decrypt...
success = crypt.DecryptBd(bdEncrypted)
if (success != true)
    print crypt.lastErrorText() + "\n";
    exit
end

#  Get the decrypted XML
decryptedXml = bdEncrypted.getString("utf-8")
print "Decrypted XML:" + "\n";
print decryptedXml + "\n";

#  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>

xmlAssertion = Chilkat::CkXml.new()
xmlAssertion.LoadXml(decryptedXml)

#  Replace the saml2:EncryptedAssertion XML subtree with the saml2:Assertion XML.
# xmlEncryptedAssertion is a CkXml
xmlEncryptedAssertion = xml.FindChild("saml2:EncryptedAssertion")
xmlEncryptedAssertion.SwapTree(xmlAssertion)

#  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:" + "\n";
print xml.getXml() + "\n";