// Copyright 2022 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//    https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

syntax = "proto3";

package s2a.proto.v2;

option go_package = "github.com/google/s2a/internal/proto/v2/s2a_go_proto";

import "internal/proto/v2/common/common.proto";
import "internal/proto/v2/s2a_context/s2a_context.proto";

enum SignatureAlgorithm {
  S2A_SSL_SIGN_UNSPECIFIED = 0;
  // RSA Public-Key Cryptography Standards #1.
  S2A_SSL_SIGN_RSA_PKCS1_SHA256 = 1;
  S2A_SSL_SIGN_RSA_PKCS1_SHA384 = 2;
  S2A_SSL_SIGN_RSA_PKCS1_SHA512 = 3;
  // ECDSA.
  S2A_SSL_SIGN_ECDSA_SECP256R1_SHA256 = 4;
  S2A_SSL_SIGN_ECDSA_SECP384R1_SHA384 = 5;
  S2A_SSL_SIGN_ECDSA_SECP521R1_SHA512 = 6;
  // RSA Probabilistic Signature Scheme.
  S2A_SSL_SIGN_RSA_PSS_RSAE_SHA256 = 7;
  S2A_SSL_SIGN_RSA_PSS_RSAE_SHA384 = 8;
  S2A_SSL_SIGN_RSA_PSS_RSAE_SHA512 = 9;
  // ED25519.
  S2A_SSL_SIGN_ED25519 = 10;
}

message AlpnPolicy {
  // If true, the application MUST perform ALPN negotiation.
  bool enable_alpn_negotiation = 1;

  // The ordered list of ALPN protocols that specify how the application SHOULD
  // negotiate ALPN during the TLS handshake.
  //
  // The application MAY ignore any ALPN protocols in this list that are not
  // supported by the application.
  repeated AlpnProtocol alpn_protocols = 2;
}

message AuthenticationMechanism {
  reserved 1;

  // Applications may specify an identity associated to an authentication
  // mechanism. Otherwise, S2A assumes that the authentication mechanism is
  // associated with the default identity. If the default identity cannot be
  // determined, the request is rejected.
  Identity identity = 3;

  oneof mechanism_oneof {
    // A token that the application uses to authenticate itself to S2A.
    string token = 2;
  }
}

message Status {
  // The status code that is specific to the application and the implementation
  // of S2A, e.g., gRPC status code.
  uint32 code = 1;

  // The status details.
  string details = 2;
}

message GetTlsConfigurationReq {
  // The role of the application in the TLS connection.
  ConnectionSide connection_side = 1;

  // The server name indication (SNI) extension, which MAY be populated when a
  // server is offloading to S2A. The SNI is used to determine the server
  // identity if the local identity in the request is empty.
  string sni = 2;
}

message GetTlsConfigurationResp {
  // Next ID: 8
  message ClientTlsConfiguration {
    reserved 4, 5;

    // The certificate chain that the client MUST use for the TLS handshake.
    // It's a list of PEM-encoded certificates, ordered from leaf to root,
    // excluding the root.
    repeated string certificate_chain = 1;

    // The minimum TLS version number that the client MUST use for the TLS
    // handshake. If this field is not provided, the client MUST use the default
    // minimum version of the client's TLS library.
    TLSVersion min_tls_version = 2;

    // The maximum TLS version number that the client MUST use for the TLS
    // handshake. If this field is not provided, the client MUST use the default
    // maximum version of the client's TLS library.
    TLSVersion max_tls_version = 3;

    // The ordered list of TLS 1.0-1.2 ciphersuites that the client MAY offer to
    // negotiate in the TLS handshake.
    repeated Ciphersuite ciphersuites = 6;

    // The policy that dictates how the client negotiates ALPN during the TLS
    // handshake.
    AlpnPolicy alpn_policy = 7;
  }

  // Next ID: 12
  message ServerTlsConfiguration {
    reserved 4, 5;

    enum RequestClientCertificate {
      UNSPECIFIED = 0;
      DONT_REQUEST_CLIENT_CERTIFICATE = 1;
      REQUEST_CLIENT_CERTIFICATE_BUT_DONT_VERIFY = 2;
      REQUEST_CLIENT_CERTIFICATE_AND_VERIFY = 3;
      REQUEST_AND_REQUIRE_CLIENT_CERTIFICATE_BUT_DONT_VERIFY = 4;
      REQUEST_AND_REQUIRE_CLIENT_CERTIFICATE_AND_VERIFY = 5;
    }

    // The certificate chain that the server MUST use for the TLS handshake.
    // It's a list of PEM-encoded certificates, ordered from leaf to root,
    // excluding the root.
    repeated string certificate_chain = 1;

    // The minimum TLS version number that the server MUST use for the TLS
    // handshake. If this field is not provided, the server MUST use the default
    // minimum version of the server's TLS library.
    TLSVersion min_tls_version = 2;

    // The maximum TLS version number that the server MUST use for the TLS
    // handshake. If this field is not provided, the server MUST use the default
    // maximum version of the server's TLS library.
    TLSVersion max_tls_version = 3;

    // The ordered list of TLS 1.0-1.2 ciphersuites that the server MAY offer to
    // negotiate in the TLS handshake.
    repeated Ciphersuite ciphersuites = 10;

    // Whether to enable TLS resumption.
    bool tls_resumption_enabled = 6;

    // Whether the server MUST request a client certificate (i.e. to negotiate
    // TLS vs. mTLS).
    RequestClientCertificate request_client_certificate = 7;

    // Returns the maximum number of extra bytes that
    // |OffloadResumptionKeyOperation| can add to the number of unencrypted
    // bytes to form the encrypted bytes.
    uint32 max_overhead_of_ticket_aead = 9;

    // The policy that dictates how the server negotiates ALPN during the TLS
    // handshake.
    AlpnPolicy alpn_policy = 11;
  }

  oneof tls_configuration {
    ClientTlsConfiguration client_tls_configuration = 1;
    ServerTlsConfiguration server_tls_configuration = 2;
  }
}

message OffloadPrivateKeyOperationReq {
  enum PrivateKeyOperation {
    UNSPECIFIED = 0;
    // When performing a TLS 1.2 or 1.3 handshake, the (partial) transcript of
    // the TLS handshake must be signed to prove possession of the private key.
    //
    // See https://www.rfc-editor.org/rfc/rfc8446.html#section-4.4.3.
    SIGN = 1;
    // When performing a TLS 1.2 handshake using an RSA algorithm, the key
    // exchange algorithm involves the client generating a premaster secret,
    // encrypting it using the server's public key, and sending this encrypted
    // blob to the server in a ClientKeyExchange message.
    //
    // See https://www.rfc-editor.org/rfc/rfc4346#section-7.4.7.1.
    DECRYPT = 2;
  }

  // The operation the private key is used for.
  PrivateKeyOperation operation = 1;

  // The signature algorithm to be used for signing operations.
  SignatureAlgorithm signature_algorithm = 2;

  // The input bytes to be signed or decrypted.
  oneof in_bytes {
    // Raw bytes to be hashed and signed, or decrypted.
    bytes raw_bytes = 4;
    // A SHA256 hash to be signed. Must be 32 bytes.
    bytes sha256_digest = 5;
    // A SHA384 hash to be signed. Must be 48 bytes.
    bytes sha384_digest = 6;
    // A SHA512 hash to be signed. Must be 64 bytes.
    bytes sha512_digest = 7;
  }
}

message OffloadPrivateKeyOperationResp {
  // The signed or decrypted output bytes.
  bytes out_bytes = 1;
}

message OffloadResumptionKeyOperationReq {
  enum ResumptionKeyOperation {
    UNSPECIFIED = 0;
    ENCRYPT = 1;
    DECRYPT = 2;
  }

  // The operation the resumption key is used for.
  ResumptionKeyOperation operation = 1;

  // The bytes to be encrypted or decrypted.
  bytes in_bytes = 2;
}

message OffloadResumptionKeyOperationResp {
  // The encrypted or decrypted bytes.
  bytes out_bytes = 1;
}

message ValidatePeerCertificateChainReq {
  enum VerificationMode {
    // The default verification mode supported by S2A.
    UNSPECIFIED = 0;
    // The SPIFFE verification mode selects the set of trusted certificates to
    // use for path building based on the SPIFFE trust domain in the peer's leaf
    // certificate.
    SPIFFE = 1;
    // The connect-to-Google verification mode uses the trust bundle for
    // connecting to Google, e.g. *.mtls.googleapis.com endpoints.
    CONNECT_TO_GOOGLE = 2;
    // Internal use only.
    RESERVED_CUSTOM_VERIFICATION_MODE_3 = 3;
    // Internal use only.
    RESERVED_CUSTOM_VERIFICATION_MODE_4 = 4;
    // Internal use only.
    RESERVED_CUSTOM_VERIFICATION_MODE_5 = 5;
  }

  message ClientPeer {
    // The certificate chain to be verified. The chain MUST be a list of
    // DER-encoded certificates, ordered from leaf to root, excluding the root.
    repeated bytes certificate_chain = 1;
  }

  message ServerPeer {
    // The certificate chain to be verified. The chain MUST be a list of
    // DER-encoded certificates, ordered from leaf to root, excluding the root.
    repeated bytes certificate_chain = 1;

    // The expected hostname of the server.
    string server_hostname = 2;

    // The UnrestrictedClientPolicy specified by the user.
    bytes serialized_unrestricted_client_policy = 3;
  }

  // The verification mode that S2A MUST use to validate the peer certificate
  // chain.
  VerificationMode mode = 1;

  oneof peer_oneof {
    ClientPeer client_peer = 2;
    ServerPeer server_peer = 3;
  }
}

message ValidatePeerCertificateChainResp {
  enum ValidationResult {
    UNSPECIFIED = 0;
    SUCCESS = 1;
    FAILURE = 2;
  }

  // The result of validating the peer certificate chain.
  ValidationResult validation_result = 1;

  // The validation details. This field is only populated when the validation
  // result is NOT SUCCESS.
  string validation_details = 2;

  // The S2A context contains information from the peer certificate chain.
  //
  // The S2A context MAY be populated even if validation of the peer certificate
  // chain fails.
  S2AContext context = 3;
}

message SessionReq {
  reserved 1;
  // The identity corresponding to the TLS configurations that MUST be used for
  // the TLS handshake.
  //
  // If a managed identity already exists, the local identity and authentication
  // mechanisms are ignored. If a managed identity doesn't exist and the local
  // identity is not populated, S2A will try to deduce the managed identity to
  // use from the SNI extension. If that also fails, S2A uses the default
  // identity (if one exists).
  Identity local_identity = 7;

  // The authentication mechanisms that the application wishes to use to
  // authenticate to S2A, ordered by preference. S2A will always use the first
  // authentication mechanism that matches the managed identity.
  repeated AuthenticationMechanism authentication_mechanisms = 2;

  oneof req_oneof {
    // Requests the certificate chain and TLS configuration corresponding to the
    // local identity, which the application MUST use to negotiate the TLS
    // handshake.
    GetTlsConfigurationReq get_tls_configuration_req = 3;

    // Signs or decrypts the input bytes using a private key corresponding to
    // the local identity in the request.
    //
    // WARNING: More than one OffloadPrivateKeyOperationReq may be sent to the
    // S2Av2 by a server during a TLS 1.2 handshake.
    OffloadPrivateKeyOperationReq offload_private_key_operation_req = 4;

    // Encrypts or decrypts the input bytes using a resumption key corresponding
    // to the local identity in the request.
    OffloadResumptionKeyOperationReq offload_resumption_key_operation_req = 5;

    // Verifies the peer's certificate chain using
    // (a) trust bundles corresponding to the local identity in the request, and
    // (b) the verification mode in the request.
    ValidatePeerCertificateChainReq validate_peer_certificate_chain_req = 6;
  }
}

message SessionResp {
  // Status of the session response.
  //
  // The status field is populated so that if an error occurs when making an
  // individual request, then communication with the S2A may continue. If an
  // error is returned directly (e.g. at the gRPC layer), then it may result
  // that the bidirectional stream being closed.
  Status status = 1;

  oneof resp_oneof {
    // Contains the certificate chain and TLS configurations corresponding to
    // the local identity.
    GetTlsConfigurationResp get_tls_configuration_resp = 2;

    // Contains the signed or encrypted output bytes using the private key
    // corresponding to the local identity.
    OffloadPrivateKeyOperationResp offload_private_key_operation_resp = 3;

    // Contains the encrypted or decrypted output bytes using the resumption key
    // corresponding to the local identity.
    OffloadResumptionKeyOperationResp offload_resumption_key_operation_resp = 4;

    // Contains the validation result, peer identity and fingerprints of peer
    // certificates.
    ValidatePeerCertificateChainResp validate_peer_certificate_chain_resp = 5;
  }
}

service S2AService {
  // SetUpSession is a bidirectional stream used by applications to offload
  // operations from the TLS handshake.
  rpc SetUpSession(stream SessionReq) returns (stream SessionResp) {}
}
