module ietf-tls-client {

    yang-version 1.1;

    namespace
      "urn:ietf:params:xml:ns:yang:ietf-tls-client";

    prefix tlsc;

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


    }
    import ietf-crypto-types {
      prefix ct;
      reference
        "RFC 9640: YANG Data Types and Groupings for Cryptography";


    }
    import ietf-truststore {
      prefix ts;
      reference
        "RFC 9641: A YANG Data Model for a Truststore";


    }
    import ietf-keystore {
      prefix ks;
      reference
        "RFC 9642: A YANG Data Model for a Keystore";


    }
    import ietf-tls-common {
      prefix tlscmn;
      reference
        "RFC 9645: 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:intensifysecurity@gmail.com>";

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

     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.

     Copyright (c) 2024 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 9645
     (https://www.rfc-editor.org/info/rfc9645); see the RFC
     itself for full legal notices.";

    revision "2024-10-10" {
      description "Initial version";
      reference
        "RFC 9645: YANG Groupings for TLS Clients and TLS Servers";

    }


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

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

    }

    feature client-ident-raw-public-key {
      description
        "Indicates that the client 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 client-ident-tls12-psk {
      if-feature tlscmn:tls12;
      description
        "Indicates that the client 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 client-ident-tls13-epsk {
      if-feature tlscmn:tls13;
      description
        "Indicates that the client 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 server-auth-x509-cert {
      description
        "Indicates that the client supports authenticating servers
       using X.509 certificates.";
      reference
        "RFC 5280:
          Internet X.509 Public Key Infrastructure Certificate
          and Certificate Revocation List (CRL) Profile";

    }

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

    }

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

    }

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

    }

    grouping tls-client-grouping {
      description
        "A reusable grouping for configuring a TLS client without
       any consideration for how an underlying TCP session is
       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-client-parameters').  This model purposely does
       not do this itself so as to provide maximum flexibility
       to consuming models.";
      container client-identity {
        nacm:default-deny-write;
        presence
          "Indicates that a TLS-level client identity has been
                configured.  This statement is present so the
                mandatory descendant nodes do not imply that this
                node must be configured.";
        description
          "Identity credentials the TLS client MAY present when
         establishing a connection to a TLS server.  If not
         configured, then client authentication is presumed to
         occur in a protocol layer above TLS.  When configured,
         and requested by the TLS server when establishing a
         TLS session, these credentials are passed in the
         Certificate message defined in Section 7.4.2 of
         RFC 5246 and Section 4.4.2 of 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 9642: 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 client-ident-x509-cert;
            container certificate {
              description
                "Specifies the client identity using a certificate.";
              uses ks:inline-or-keystore-end-entity-cert-with-key-grouping {
                refine inline-or-keystore/inline/inline-definition {
                  must
                    'not(public-key-format) or derived-from-or-self'
                      + '(public-key-format, "ct:subject-public-key-'
                      + 'info-format")';
                }

                refine inline-or-keystore/central-keystore/central-keystore-reference/asymmetric-key {
                  must
                    'not(deref(.)/../ks:public-key-format) or '
                      + 'derived-from-or-self(deref(.)/../ks:public-'
                      + 'key-format, "ct:subject-public-key-info-'
                      + 'format")';
                }
              }
            }  // container certificate
          }  // case certificate

          case raw-public-key {
            if-feature client-ident-raw-public-key;
            container raw-private-key {
              description
                "Specifies the client identity using a raw
               private key.";
              uses ks:inline-or-keystore-asymmetric-key-grouping {
                refine inline-or-keystore/inline/inline-definition {
                  must
                    'not(public-key-format) or derived-from-or-self'
                      + '(public-key-format, "ct:subject-public-key-'
                      + 'info-format")';
                }

                refine inline-or-keystore/central-keystore/central-keystore-reference {
                  must
                    'not(deref(.)/../ks:public-key-format) or '
                      + 'derived-from-or-self(deref(.)/../ks:public-'
                      + 'key-format, "ct:subject-public-key-info-'
                      + 'format")';
                }
              }
            }  // container raw-private-key
          }  // case raw-public-key

          case tls12-psk {
            if-feature client-ident-tls12-psk;
            container tls12-psk {
              description
                "Specifies the client identity using a PSK (pre-shared
               or pairwise symmetric key).";
              uses ks:inline-or-keystore-symmetric-key-grouping;

              leaf id {
                type string;
                description
                  "The key 'psk_identity' value used in the TLS
                 'ClientKeyExchange' message.";
                reference
                  "RFC 4279: Pre-Shared Key Ciphersuites for
                  	  Transport Layer Security (TLS)";

              }
            }  // container tls12-psk
          }  // case tls12-psk

          case tls13-epsk {
            if-feature client-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).  EPSKs MUST NOT be
               imported for (D)TLS 1.2 or prior versions.  When
               PSKs are provisioned out of band, the PSK identity
               and the Key Derivation Function (KDF) hash algorithm
               to be used with the PSK MUST also be provisioned.

               The structure of this container is designed to satisfy
               the requirements in Section 4.2.11 of RFC 8446, the
               recommendations from Section 6 of RFC 9257, and the
               EPSK input fields detailed in Section 5.1 of RFC 9258.
               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
                 RFC 9257: Guidance for External Pre-Shared Key
                	  (PSK) Usage in TLS
                 RFC 9258: Importing External Pre-Shared Keys
                	  (PSKs) for TLS 1.3";

              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 RFC 9257, 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
                   RFC 9257: Guidance for External Pre-Shared Key
                  	  (PSK) Usage in TLS";

              }

              leaf hash {
                type tlscmn:epsk-supported-hash;
                default "sha-256";
                description
                  "As per Section 4.2.11 of RFC 8446, for EPSKs,
                 the hash algorithm MUST be set when the PSK is
                 established; otherwise, 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 5.1 of RFC 9258, context MUST
                 include the context used to determine the EPSK,
                 if any exists.  For example, context may include
                 information about peer roles or identities
                 to mitigate Selfie-style reflection attacks.
                 Since the EPSK is a key derived from an external
                 protocol or a sequence of protocols, context MUST
                 include a channel binding for the deriving
                 protocols (see RFC 5056).  The details of this
                 binding are protocol specific and out of scope
                 for this document.";
                reference
                  "RFC 9258: Importing External Pre-Shared Keys
                  	  (PSKs) for TLS 1.3";

              }

              leaf target-protocol {
                type uint16;
                description
                  "As per Section 3 of RFC 9258, the protocol
                 for which a PSK is imported for use.";
                reference
                  "RFC 9258: Importing External Pre-Shared Keys
                  	  (PSKs) for TLS 1.3";

              }

              leaf target-kdf {
                type uint16;
                description
                  "As per Section 3 of RFC 9258, the Key Derivation
                 Function (KDF) for which a PSK is imported for
                 use.";
                reference
                  "RFC 9258: Importing External Pre-Shared Keys
                  	  (PSKs) for TLS 1.3";

              }
            }  // container tls13-epsk
          }  // case tls13-epsk
        }  // choice auth-type
      }  // container client-identity

      container server-authentication {
        nacm:default-deny-write;
        must
          "ca-certs or ee-certs or raw-public-keys or tls12-psks
                    or tls13-epsks";
        description
          "Specifies how the TLS client can authenticate TLS servers.
         Any combination of credentials is additive and unordered.

         Note that no configuration is required for authentication
         based on PSK (pre-shared or pairwise symmetric key) as
         the key is necessarily the same as configured in the
         '../client-identity' node.";
        container ca-certs {
          if-feature server-auth-x509-cert;
          presence
            "Indicates that Certification Authority (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 CA certificates used by the TLS client to
           authenticate TLS server certificates.  A server
           certificate is authenticated if it has a valid chain of
           trust to a configured CA certificate.";
          reference
            "RFC 9641: A YANG Data Model for a Truststore";

          uses ts:inline-or-truststore-certs-grouping;
        }  // container ca-certs

        container ee-certs {
          if-feature server-auth-x509-cert;
          presence
            "Indicates that End-Entity (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 server certificates (i.e., EE certificates) used
           by the TLS client to authenticate certificates presented
           by TLS servers.  A server certificate is authenticated if
           it is an exact match to a configured server certificate.";
          reference
            "RFC 9641: A YANG Data Model for a Truststore";

          uses ts:inline-or-truststore-certs-grouping;
        }  // container ee-certs

        container raw-public-keys {
          if-feature server-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 client to
           authenticate raw public keys presented by the TLS
           server.  A raw public key is authenticated if it
           is an exact match to a configured raw public key.";
          reference
            "RFC 9641: 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/central-truststore/central-truststore-reference {
              must
                'not(deref(.)/../ts:public-key/ts:public-key-'
                  + 'format[not(derived-from-or-self(., "ct:subject-'
                  + 'public-key-info-format"))])';
            }
          }
        }  // container raw-public-keys

        leaf tls12-psks {
          if-feature server-auth-tls12-psk;
          type empty;
          description
            "Indicates that the TLS client can authenticate TLS servers
           using configured PSKs (pre-shared or pairwise symmetric
           keys).

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

        leaf tls13-epsks {
          if-feature server-auth-tls13-epsk;
          type empty;
          description
            "Indicates that the TLS client can authenticate TLS servers
           using configured External PSKs (pre-shared keys).

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

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

      container keepalives {
        nacm:default-deny-write;
        if-feature tls-client-keepalives;
        description
          "Configures the keepalive policy for the TLS client.";
        leaf peer-allowed-to-send {
          type empty;
          description
            "Indicates that the remote TLS server is allowed to send
           HeartbeatRequest messages, as defined by RFC 6520,
           to this TLS client.";
          reference
            "RFC 6520: Transport Layer Security (TLS) and Datagram
            Transport Layer Security (DTLS) Heartbeat Extension";

        }

        container test-peer-aliveness {
          presence
            "Indicates that the TLS client proactively tests the
                  aliveness of the remote TLS server.";
          description
            "Configures the keepalive policy to proactively test
           the aliveness of the TLS server.  An unresponsive
           TLS server is dropped after approximately max-wait
           * max-attempts seconds.  The TLS client MUST send
           HeartbeatRequest messages, as defined in RFC 6520.";
          reference
            "RFC 6520: Transport Layer Security (TLS) and Datagram
            Transport Layer Security (DTLS) Heartbeat Extension";

          leaf max-wait {
            type uint16 {
              range "1..max";
            }
            units "seconds";
            default "30";
            description
              "Sets the amount of time in seconds, after which a
             TLS-level message will be sent to test the
             aliveness of the TLS server if no data has been
             received from the TLS server.";
          }

          leaf max-attempts {
            type uint8;
            default "3";
            description
              "Sets the maximum number of sequential keepalive
             messages that can fail to obtain a response from
             the TLS server before assuming the TLS server is
             no longer alive.";
          }
        }  // container test-peer-aliveness
      }  // container keepalives
    }  // grouping tls-client-grouping
  }  // module ietf-tls-client