[email protected]

module ietf-tpm-remote-attestation-stream {
  yang-version 1.1;
  namespace 
     "urn:ietf:params:xml:ns:yang:ietf-tpm-remote-attestation-stream";
  prefix tras;

  import ietf-subscribed-notifications { 
    prefix sn;
    reference
      "RFC 8639: Subscription to YANG Notifications";    
  }
  import ietf-tpm-remote-attestation { 
    prefix tpm; 
    reference  
      "draft-ietf-rats-yang-tpm-charra";  
  }
  import ietf-yang-structure-ext { 
    prefix sx; 
    reference
      "draft-ietf-netmod-yang-data-ext";
  }
   
  organization "IETF";
  contact
    "WG Web:   <http://tools.ietf.org/wg/rats/>
     WG List:  <mailto:rats@ietf.org>

     Editor:   Eric Voit
               <mailto:evoit@cisco.com>";
               
  description
    "This module contains conceptual YANG specifications for  
     subscribing to attestation streams being generated from TPM chips.
    
     Copyright (c) 2020 IETF Trust and the persons identified
     as authors of the code. All rights reserved.

     Redistribution and use in source and binary forms, with
     or without modification, is permitted pursuant to, and
     subject to the license terms contained in, the Simplified
     BSD License set forth in Section 4.c of the IETF Trust's
     Legal Provisions Relating to IETF Documents
     (https://trustee.ietf.org/license-info).
     
     Redistribution and use in source and binary forms, with or
     without modification, is permitted pursuant to, and subject to
     the license terms contained in, the Simplified BSD License set
     forth in Section 4.c of the IETF Trust's Legal Provisions
     Relating to IETF Documents
     (https://trustee.ietf.org/license-info).

     This version of this YANG module is part of RFC XXXX
     (https://www.rfc-editor.org/info/rfcXXXX); see the RFC
     itself for full legal notices.

     The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL',
     'SHALL NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED',
     'NOT RECOMMENDED', 'MAY', and 'OPTIONAL' in this document
     are to be interpreted as described in BCP 14 (RFC 2119)
     (RFC 8174) when, and only when, they appear in all
     capitals, as shown here.";
  
  revision 2020-06-05 {
    description
      "Initial version.";    
    reference 
      "draft-birkholz-rats-network-device-subscription";
  }
   
  /*
   * IDENTITIES
   */
   
  identity pcr-unsubscribable {
    base sn:establish-subscription-error;
    description
      "Requested PCR is subscribable by the Attester.";
  }
  
  
  /*
   * Groupings
   */ 

  grouping heartbeat {
    description
      "Allows an Attester to push verifiable, current TPM PCR values even
      when there have been no recent changes to PCRs.";    
    leaf tpm20-subscription-heartbeat {
      type uint16;
      description
        "Number of seconds before the Attestation stream should send a new
        notification with a fresh quote.  This allows confirmation 
        that the PCR values haven't changed since the last 
        tpm20-attestation.";
    }
  }
  
  
  /*
   * RPCs
   */ 
  
  augment "/sn:establish-subscription/sn:input" {
    when 'derived-from-or-self(sn:stream, "attestation")';
    description
      "This augmentation adds a nonce to as a subscription parameters
       that apply specifically to datastore updates to RPC input.";
    uses tpm:nonce;
    leaf-list pcr-index {
      type tpm:pcr;
      min-elements 1;
      description
        "The numbers/indexes of the PCRs. This will act as a filter for the 
        subscription so that 'tpm-extend' notifications related to 
        non-requested PCRs will not be sent to a subscriber.";
    }
  }
  
  /*
   * NOTIFICATIONS
   */  

  notification tpm-extend {
    description
      "This notification indicates that a PCR has extended within a TPM based
      cryptoprocessor.  In less that 10 seconds, it should be followed with 
      either a tpm12-attestation or tpm20-attestation notification.";
    uses tpm:tpm-name;
    leaf pcr-index-changed {
      type tpm:pcr;
      mandatory true;
      description
        "The number of the PCR extended.";
    }
    list attested-event {
      description
        "A set of events which extended an Attester PCR.  The sequence of 
        elements represented in list must match the sequence of events  
        placed into the TPM.";
      container attested-event {
        description
          "An instance of an event which extended an Attester PCR";
        leaf extended-with {
          type binary;
          mandatory true;
          description
            "Information extending the PCR.";
        }
        leaf event-type {
          type identityref {
            base tpm:attested-event-log-type;
          }
          description
            "Indicates what kind of event happened the Attester thought was 
            worthy of recording in a PCR.";  
        }
        anydata event-details {
          description
            "Any structure reference 'event-type' contains supporting 
            information which allows an Attester to evaluate the trust 
            implications.
            
            Event details may be populated with YANG log structures defined
            at the bottom of this module.";
        }
      }
    }
  }  

  notification tpm12-attestation {
    if-feature "tpm:TPM12";
    description
      "Contains an instance of TPM1.2 style signed cryptoprocessor 
      measurements.  It is supplemented by unsigned Attester information.";
    uses tpm:tpm12-attestation;
  }

  notification tpm20-attestation {
    if-feature "tpm:TPM20";
    description
      "Contains an instance of TPM2 style signed cryptoprocessor 
      measurements.  It is supplemented by unsigned Attester information.";
    uses tpm:tpm20-attestation;
  } 


  /*
   * DATA NODES
   */  

  augment "/tpm:rats-support-structures" {
    description
      "Defines platform wide 'attestation' stream subscription parameters.";   
    leaf marshalling-period {
      config true;
      type uint8;
      default 5;
      description
        "The maximum number of seconds between the time an event extends a PCR, 
        and the 'tpm-extend' notification which reports it to a subscribed
        Verifier.  This period allows multiple extend operations bundled 
        together and handled as a group.";
    }
    leaf tpm12-subscribed-signature-scheme {
      if-feature "tpm:TPM12";
      type leafref {
        path "../tpm:supported-algos"; 
          /* a specific algorithm, need to check syntax */
      }
      description
        "A single signature-scheme which will be used to sign the evidence 
        from a TPM 1.2. which is then placed onto the 'attestation' event
        stream.";
    }
    leaf tpm20-subscribed-signature-scheme {
      if-feature "tpm:TPM20";
      type leafref {
        path "../tpm:supported-algos"; 
          /* a specific algorithm, need to check syntax */
      }
      description
        "A single signature-scheme which will be used to sign the evidence 
        from a TPM 2.0. which is then placed onto the 'attestation' event
        stream.";
    }    
    uses heartbeat{
      if-feature "tpm:TPM20";
    }
  }
  
  augment "/tpm:rats-support-structures/tpm:tpms" {
    description
      "Allows the configuration 'attestation' stream parameters for a TPM.";  
    leaf leafref-to-keystore {
      config true;
      type string;
      description 
        "needs to be replaced with Reference to keystore draft.";
    }
    choice subscribable {
      config true;
      description
        "Indicates that the set of notifications which comprise the attestation 
        stream can be modified or tuned by a network adminsitrator.";
      case tpm12-stream {
        if-feature "tpm:TPM12";
        description
          "Configuration elements for a TPM1.2 event stream.";
        leaf-list tpm12-pcr-index {
          type tpm:pcr;
          description
            "The numbers/indexes of the PCRs which can be subscribed.";
        }
      }
      case tpm20-stream {
        if-feature "tpm:TPM20";
        description
          "Configuration elements for a TPM2.0 event stream.";
        leaf-list tpm20-pcr-index {
          type tpm:pcr;
          description
            "The numbers/indexes of the PCRs which can be subscribed.";
        }
        /* We need to decide if more than one hash-algo is subscribable */
      }
    }
  }  

  
  /*
   * STRUCTURES - these contain the schema of reportable event types
   */    
  
   sx:structure bios-event-log {
     when 'derived-from(../event-type, "bios-event-log")';
     description
       "BIOS/UEFI event log format";
     uses tpm:bios-event-log;
   }
      
   sx:structure ima-event-log {
     when 'derived-from(../event-type, "ima-event-log")';
     description
       "IMA event log format";
     uses tpm:ima-event-log;
   }
}