module ietf-tls-server {
  yang-version 1.1;
  namespace "urn:ietf:params:xml:ns:yang:ietf-tls-server";
  prefix tlss;

  import ietf-netconf-acm {
    prefix nacm;
    reference
      "RFC 8341: Network Configuration Access Control Model";
  }

  import ietf-crypto-types {
    prefix ct;
    reference
      "RFC AAAA: YANG Data Types and Groupings for Cryptography";
  }

  import ietf-truststore {
    prefix ts;
    reference
      "RFC BBBB: A YANG Data Model for a Truststore";
  }

  import ietf-keystore {
    prefix ks;
    reference
      "RFC CCCC: A YANG Data Model for a Keystore";
  }

  import ietf-tls-common {
    prefix tlscmn;
    reference
      "RFC FFFF: YANG Groupings for TLS Clients and TLS Servers";
  }

  organization
    "IETF NETCONF (Network Configuration) Working Group";

  contact
    "WG List:  NETCONF WG list <mailto:netconf@ietf.org>
     WG Web:   https://datatracker.ietf.org/wg/netconf
     Author:   Kent Watsen <mailto:kent+ietf@watsen.net>
     Author:   Jeff Hartley <mailto:jeff.hartley@commscope.com>";

  description
    "This module defines reusable groupings for TLS servers that
     can be used as a basis for specific TLS server instances.

     Copyright (c) 2023 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 Revised
     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 FFFF
     (https://www.rfc-editor.org/info/rfcFFFF); 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 2023-04-17 {
    description
      "Initial version";
    reference
      "RFC FFFF: YANG Groupings for TLS Clients and TLS Servers";
  }

  // Features

  feature tls-server-keepalives {
    description
      "Per socket TLS keepalive parameters are configurable for
       TLS servers on the server implementing this feature.";
  }

  feature server-ident-x509-cert {
    description
      "Indicates that the server supports identifying itself
       using X.509 certificates.";
    reference
      "RFC 5280:
         Internet X.509 Public Key Infrastructure Certificate
         and Certificate Revocation List (CRL) Profile";
  }

  feature server-ident-raw-public-key {
    description
      "Indicates that the server supports identifying itself
       using raw public keys.";
    reference
      "RFC 7250:
         Using Raw Public Keys in Transport Layer Security (TLS)
         and Datagram Transport Layer Security (DTLS)";
  }

  feature server-ident-tls12-psk {
    description
      "Indicates that the server supports identifying itself
       using TLS-1.2 PSKs (pre-shared or pairwise-symmetric keys).";
    reference
      "RFC 4279:
         Pre-Shared Key Ciphersuites for Transport Layer Security
         (TLS)";
  }

  feature server-ident-tls13-epsk {
    description
      "Indicates that the server supports identifying itself
       using TLS-1.3 External PSKs (pre-shared keys).";
    reference
      "RFC 8446:
         The Transport Layer Security (TLS) Protocol Version 1.3";
  }

  feature client-auth-supported {
    description
      "Indicates that the configuration for how to authenticate
       clients can be configured herein.  TLS-level client
       authentication may not be needed when client authentication
       is expected to occur only at another protocol layer.";
  }

  feature client-auth-x509-cert {
    description
      "Indicates that the server supports authenticating clients
       using X.509 certificates.";
    reference
      "RFC 5280:
         Internet X.509 Public Key Infrastructure Certificate
         and Certificate Revocation List (CRL) Profile";
  }

  feature client-auth-raw-public-key {
    description
      "Indicates that the server supports authenticating clients
       using raw public keys.";
    reference
      "RFC 7250:
         Using Raw Public Keys in Transport Layer Security (TLS)
         and Datagram Transport Layer Security (DTLS)";
  }

  feature client-auth-tls12-psk {
    description
      "Indicates that the server supports authenticating clients
       using PSKs (pre-shared or pairwise-symmetric keys).";
    reference
      "RFC 4279:
         Pre-Shared Key Ciphersuites for Transport Layer Security
         (TLS)";
  }

  feature client-auth-tls13-epsk {
    description
      "Indicates that the server supports authenticating clients
       using TLS-1.3 External PSKs (pre-shared keys).";
    reference
      "RFC 8446:
         The Transport Layer Security (TLS) Protocol Version 1.3";
  }

  // Groupings

  grouping tls-server-grouping {
    description
      "A reusable grouping for configuring a TLS server without
       any consideration for how underlying TCP sessions are
       established.

       Note that this grouping uses fairly typical descendant
       node names such that a stack of 'uses' statements will
       have name conflicts.  It is intended that the consuming
       data model will resolve the issue (e.g., by wrapping
       the 'uses' statement in a container called
       'tls-server-parameters').  This model purposely does
       not do this itself so as to provide maximum flexibility
       to consuming models.";

    container server-identity {
      nacm:default-deny-write;
      description
        "A locally-defined or referenced end-entity certificate,
         including any configured intermediate certificates, the
         TLS server will present when establishing a TLS connection
         in its Certificate message, as defined in Section 7.4.2
         in RFC 5246 and Section 4.4.2 in RFC 8446.";
      reference
        "RFC 5246: The Transport Layer Security (TLS) Protocol
                   Version 1.2
         RFC 8446: The Transport Layer Security (TLS) Protocol
                   Version 1.3
         RFC CCCC: A YANG Data Model for a Keystore";
      choice auth-type {
        mandatory true;
        description
          "A choice amongst authentication types, of which one must
           be enabled (via its associated 'feature') and selected.";
        case certificate {
          if-feature "server-ident-x509-cert";
          container certificate {
            description
              "Specifies the server identity using a certificate.";
            uses
              "ks:inline-or-keystore-end-entity-cert-with-key-"
              + "grouping" {
              refine "inline-or-keystore/inline/inline-definition" {
                must 'derived-from-or-self(public-key-format,'
                   + ' "ct:subject-public-key-info-format")';
              }
              refine "inline-or-keystore/keystore/keystore-reference"
                   + "/asymmetric-key" {
                must 'derived-from-or-self(deref(.)/../ks:public-'
                   + 'key-format, "ct:subject-public-key-info-'
                   + 'format")';
              }
            }
          }
        }
        case raw-private-key {
          if-feature "server-ident-raw-public-key";
          container raw-private-key {
            description
              "Specifies the server identity using a raw
               private key.";
            uses ks:inline-or-keystore-asymmetric-key-grouping {
              refine "inline-or-keystore/inline/inline-definition" {
                must 'derived-from-or-self(public-key-format,'
                   + ' "ct:subject-public-key-info-format")';
              }
              refine
                "inline-or-keystore/keystore/keystore-reference" {
                must 'derived-from-or-self(deref(.)/../ks:public-'
                   + 'key-format, "ct:subject-public-key-info-'
                   + 'format")';
              }
            }
          }
        }
        case tls12-psk {
          if-feature "server-ident-tls12-psk";
          container tls12-psk {
            description
              "Specifies the server identity using a PSK (pre-shared
               or pairwise-symmetric key).";
            uses ks:inline-or-keystore-symmetric-key-grouping;
            leaf id_hint {
              type string;
              description
                "The key 'psk_identity_hint' value used in the TLS
                 'ServerKeyExchange' message.";
              reference
                "RFC 4279: Pre-Shared Key Ciphersuites for
                           Transport Layer Security (TLS)";
            }
          }
        }
        case tls13-epsk {
          if-feature "server-ident-tls13-epsk";
          container tls13-epsk {
            description
              "An External Pre-Shared Key (EPSK) is established
              or provisioned out-of-band, i.e., not from a TLS
              connection.  An EPSK is a tuple of (Base Key,
              External Identity, Hash).  External PSKs MUST
              NOT be imported for (D)TLS 1.2 or prior versions.
              When PSKs are provisioned out of band, the PSK
              identity and the KDF hash algorithm to be used
              with the PSK MUST also be provisioned.

              The structure of this container is designed
              to satisfy the requirements of RFC 8446
              Section 4.2.11, the recommendations from
              I-D ietf-tls-external-psk-guidance Section 6,
              and the EPSK input fields detailed in
              I-D draft-ietf-tls-external-psk-importer
              Section 3.1.  The base-key is based upon
              ks:inline-or-keystore-symmetric-key-grouping
              in order to provide users with flexible and
              secure storage options.";
            reference
              "RFC 8446: The Transport Layer Security (TLS)
                         Protocol Version 1.3
               I-D.ietf-tls-external-psk-importer: Importing
                         External PSKs for TLS
               I-D.ietf-tls-external-psk-guidance: Guidance
                         for External PSK Usage in TLS";
            uses ks:inline-or-keystore-symmetric-key-grouping;
            leaf external-identity {
              type string;
              mandatory true;
              description
                "As per Section 4.2.11 of RFC 8446, and Section 4.1
                 of I-D. ietf-tls-external-psk-guidance: A sequence
                 of bytes used to identify an EPSK. A label for a
                 pre-shared key established externally.";
              reference
                "RFC 8446: The Transport Layer Security (TLS)
                           Protocol Version 1.3
                 I-D.ietf-tls-external-psk-guidance:
                           Guidance for External PSK Usage in TLS";
            }
            leaf hash {
              type tlscmn:epsk-supported-hash;
              mandatory true;
              description
                "As per Section 4.2.11 of RFC 8446, for externally
                 established PSKs, the Hash algorithm MUST be set
                 when the PSK is established or default to SHA-256
                 if no such algorithm is defined.  The server MUST
                 ensure that it selects a compatible PSK (if any)
                 and cipher suite.  Each PSK MUST only be used
                 with a single hash function.";
              reference
                "RFC 8446: The Transport Layer Security (TLS)
                           Protocol Version 1.3";
            }
            leaf context {
              type string;
              description
                "As per Section 4.1 of I-D.
                 ietf-tls-external-psk-guidance: Context
                 may include information about peer roles or
                 identities to mitigate Selfie-style reflection
                 attacks [Selfie].  If the EPSK is a key derived
                 from some other protocol or sequence of protocols,
                 context MUST include a channel binding for the
                 deriving protocols [RFC5056].  The details of
                 this binding are protocol specific.";
              reference
                "I-D.ietf-tls-external-psk-importer:
                           Importing External PSKs for TLS
                 I-D.ietf-tls-external-psk-guidance:
                           Guidance for External PSK Usage in TLS";
            }
            leaf target-protocol {
              type uint16;
              description
                "As per Section 3.1 of I-D.
                 ietf-tls-external-psk-guidance: The protocol
                 for which a PSK is imported for use.";
              reference
                "I-D.ietf-tls-external-psk-importer:
                           Importing External PSKs for TLS";
            }
            leaf target-kdf {
              type uint16;
              description
                "As per Section 3.1 of I-D.
                 ietf-tls-external-psk-guidance: The specific Key
                 Derivation Function (KDF) for which a PSK is
                 imported for use.";
              reference
                "I-D.ietf-tls-external-psk-importer:
                           Importing External PSKs for TLS";
            }
          }
        }
      }
    } // container server-identity

    container client-authentication {
      if-feature "client-auth-supported";
      nacm:default-deny-write;
      must 'ca-certs or ee-certs or raw-public-keys or tls12-psks
        or tls13-epsks';
      presence
        "Indicates that client authentication is supported (i.e.,
         that the server will request clients send certificates).
         If not configured, the TLS server SHOULD NOT request the
         TLS clients provide authentication credentials.";
      description
        "Specifies how the TLS server can authenticate TLS clients.
         Any combination of credentials is additive and unordered.

         Note that no configuration is required for PSK (pre-shared
         or pairwise-symmetric key) based authentication as the key
         is necessarily the same as configured in the '../server-
         identity' node.";
      container ca-certs {
        if-feature "client-auth-x509-cert";
        presence
          "Indicates that CA certificates have been configured.
           This statement is present so the mandatory descendant
           nodes do not imply that this node must be configured.";
        description
          "A set of certificate authority (CA) certificates used by
           the TLS server to authenticate TLS client certificates.
           A client certificate is authenticated if it has a valid
           chain of trust to a configured CA certificate.";
        reference
          "RFC BBBB: A YANG Data Model for a Truststore";
        uses ts:inline-or-truststore-certs-grouping;
      }
      container ee-certs {
        if-feature "client-auth-x509-cert";
        presence
          "Indicates that EE certificates have been configured.
           This statement is present so the mandatory descendant
           nodes do not imply that this node must be configured.";
        description
          "A set of client certificates (i.e., end entity
           certificates) used by the TLS server to authenticate
           certificates presented by TLS clients. A client
           certificate is authenticated if it is an exact
           match to a configured client certificate.";
        reference
          "RFC BBBB: A YANG Data Model for a Truststore";
        uses ts:inline-or-truststore-certs-grouping;
      }
      container raw-public-keys {
        if-feature "client-auth-raw-public-key";
        presence
          "Indicates that raw public keys have been configured.
           This statement is present so the mandatory descendant
           nodes do not imply that this node must be configured.";
        description
          "A set of raw public keys used by the TLS server to
           authenticate raw public keys presented by the TLS
           client.  A raw public key is authenticated if it
           is an exact match to a configured raw public key.";
        reference
          "RFC BBBB: A YANG Data Model for a Truststore";
        uses ts:inline-or-truststore-public-keys-grouping {
          refine "inline-or-truststore/inline/inline-definition/"
               + "public-key" {
            must 'derived-from-or-self(public-key-format,'
               + ' "ct:subject-public-key-info-format")';
          }
          refine "inline-or-truststore/truststore/truststore-"
               + "reference" {
            must 'not(deref(.)/../ts:public-key/ts:public-key-'
               + 'format[not(derived-from-or-self(., "ct:subject-'
               + 'public-key-info-format"))])';
          }
        }
      }
      leaf tls12-psks {
        if-feature "client-auth-tls12-psk";
        type empty;
        description
          "Indicates that the TLS server can authenticate TLS clients
           using configured PSKs (pre-shared or pairwise-symmetric
           keys).

           No configuration is required since the PSK value is the
           same as PSK value configured in the 'server-identity'
           node.";
      }
      leaf tls13-epsks {
        if-feature "client-auth-tls13-epsk";
        type empty;
        description
          "Indicates that the TLS 1.3 server can authenticate TLS
           clients using configured external PSKs (pre-shared keys).

           No configuration is required since the PSK value is the
           same as PSK value configured in the 'server-identity'
           node.";
      }
    } // container client-authentication

    container hello-params {
      nacm:default-deny-write;
      if-feature "tlscmn:hello-params";
      uses tlscmn:hello-params-grouping;
      description
        "Configurable parameters for the TLS hello message.";
    } // container hello-params

    container keepalives {
      nacm:default-deny-write;
      if-feature "tls-server-keepalives";
      description
        "Configures the keepalive policy for the TLS server.";
      leaf peer-allowed-to-send {
        type empty;
        description
          "Indicates that the remote TLS client is allowed to send
           HeartbeatRequest messages, as defined by RFC 6520
           to this TLS server.";
        reference
          "RFC 6520: Transport Layer Security (TLS) and Datagram
           Transport Layer Security (DTLS) Heartbeat Extension";
      }
      container test-peer-aliveness {
        presence
          "Indicates that the TLS server proactively tests the
           aliveness of the remote TLS client.";
        description
          "Configures the keep-alive policy to proactively test
           the aliveness of the TLS client.  An unresponsive
           TLS client is dropped after approximately max-wait
           * max-attempts seconds.";
        leaf max-wait {
          type uint16 {
            range "1..max";
          }
          units "seconds";
          default "30";
          description
            "Sets the amount of time in seconds after which if
             no data has been received from the TLS client, a
             TLS-level message will be sent to test the
             aliveness of the TLS client.";
        }
        leaf max-attempts {
          type uint8;
          default "3";
          description
            "Sets the maximum number of sequential keep-alive
             messages that can fail to obtain a response from
             the TLS client before assuming the TLS client is
             no longer alive.";
        }
      }
    } // container keepalives
  } // grouping tls-server-grouping

}