AD RMS: Document consumption overview.

How recipient gets access to RMS-protect file\email? What does it send to RMS server? How to decrypt symmetric key and decrypt document? These questions will be answered within this post today.

Numeration on a diagram below is continuing from previous post. The first 6 steps explain document protection process. Our recipient (User#2 on a diagram) received somehow RMS-protected document. User#2 might copy it from network share, or get it by email, etc. Since document protected with appropriate RMS-template this protected document isn’t available for operation unless these rights were granted in RMS-template, or granted directly to this user. Even if abuser receives protected document it won’t be available for opening. How safe is our protection? Insofar as RSA 1024 encryption protocol safe (with this protocol protected symmetric key).

User#2 got:

  • Original document protected with symmetric key
  • Publish license (encrypted with SLC public key and signed with user’s CLC private key):
  •     Symmetric key encrypted with SLC public key
  •     List of rights expressed in XrML format
  •     Copy of user’s CLC certificate

How Consume protected document_partII_v.1.0

Legend

 

7. User “unpacks” protected document takes out Publish License

8. User sends copy of its own RAC certificate (as you remember RAC is used to identity user) & Publish License to RMS server.

IMPORTANT: content (RMS-protected file\email) is never sent to RMS server. NEVER.

9. RMS server using its own private key decrypts Publish License and symmetric key. As of now RMS server has symmetric key, but hasn’t decrypted content (still on User#2 computer).

10. RMS server extracts list of rights from Publish License  and compares list of rights with user identity (RMS server has user’s RAC file, so RMS server knows exactly who asks for right to open a file).

11. RMS server generates Use License and puts there:

  • Symmetric key protected with RAC public key. As of now only RAC private key owner can decrypt this symmetric key.
  • New list of rights with appropriate entries only (e.g.User#2 – Read & Print)
  • RMS server signs Use License with its private key (SLC).

12. RMS server sends Use License back to requester (User#2).

13. User#2 (actually RMS-client) retrieves symmetric key from Use License and decrypt it with its own CLC private key.

14. Using symmetric key RMS-client finally decrypts document.

15. User’s rights are applied for decrypted document. As of now user can manage document according to his right in Use License (list of rights XrML document).

That is all.

AD RMS: Client machine activation

It’s time for client activation. As of now we have:

  • Client PC with Security Processor Certificate (SPC)
  • AD RMS server with Service Licensing Certificate (SLC)
  • Server with Active Directory Domain Service role.
  • SQL server with RMS databases.

So, client has to be activate first to start protect documents. As you remember when you installed AD RMS server role you also registered Service Connection Point. This is specially entry in Active Directory which allows clientsto identifies the connection URL for the service to the AD RMS-enabled clients.

1. Client “asks” AD DS for Service Connection Point, looks like “give me the URL where AD RMS role is hosted”. This step is very important: if client activation doesn’t happen I recommend to start first of all with “Get RMS SCP” command from AD RMS Toolkit . Here you can find some trick how to force RMS activation on client side without appropriate entry in Active Directory. The secret in client registry.

2. As the answer on client request it gets appropriate URL AD RMS Certification pipeline: https://<RMS>/certification.asmx

3. Using URL which client got on a step above, it asks RMS server for Rights Account Certificate (RAC). This request for RAC contains user’s Security Processor Certificate (SPC). Understanding AD RMS Ceritificates. 

4. AD RMS server unpack public key from user’s SPC for future purposes (step 9).

5. AD RMS server sends request to AD DS for user’s email address. Why does RMS require SMTP address for user? Why RMS require SMTP entry at least (instead of real email address in your email exchange system)? Good questions, think so? I’ll publish answer at next post, just leaving this question for you…

6. Probably this isn’t a first user’s attempt to ask for RAC, probably RMS server already had issued RAC for user earlier? RMS checks RAC for appropriate user in SQL server. The next step depends on RAC availability in SQL server: if RAC already exist server brings it back for user (not interesting case for us), otherwise server generates new RAC.

7. Server generates key pair: private and public key for RAC. The key length might be up to RSA 2048 bit if your RMS server already was patched and configured for Cryptographic Mode 2

8. AD RMS server encrypts new key pair with SLC public key and store result (BLOB) in SQL. So, next time when RMS-client asks for RAC , RMS server will bring back certificate with these public\private keys in it (see step 6).

9. Finally (for this stage) RMS generates new RAC certificate and put there:

  • public key
  • private key encrypted with user’s public key from SPC (server got this SPC public key on step#4).

Server signs RAC certificate with public key from SLC.

RAC certificate is ready to be sent to user. Done!

10. It’s time to order Client Licensor Certificate (CLC), which can be submitted only with RMS licensing web role. What the URL for this licensing role?

It is obvious from AD RMS console, but it isn’t obvious for client. Client asks for licensing URL and substitutes “Certification.amsx” in pipeline for “Publishing.asmx”

RMS COnsole2

 

11. Client asks fro CLC using URL address which it got on a step above.

12. RMS server generates key pair: public and private key for CLC, generates new certificate and put there these 2 keys:

  • public key
  • private key protected with public key from RAC. So, only RAC’s private key owner can decrypt CLC private key.

Server signs new CLC certificate with public key from SLC.

Pay attention that CLC certificate, neither keys aren’t saved in SQL, it means that RMS server generate these keys\certificate each time when client asks for them. How often it happens? Obviously not so often: when end-user uses new client PC. In the rest cases end-users uses CLC to sing Publishing license which was requested earlier.

CLS is done and ready to be sent to user back with RMS server SLC.

Congratulation. We are ready to protect and consume protected documents.

 

Machine Activation_v.1.0