dbus/cryptohome/key.proto

// Copyright (c) 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
//
// Provides wire-type for cryptohome Key objects.  It does not
// represent the entirety of the bookkeeping data needed by Cryptohome.
//
// Anything in this file may be persisted on disk.  Update carefully!

syntax = "proto2";

option optimize_for = LITE_RUNTIME;

package cryptohome;

message KeyAuthorizationSecretUsage {
  optional bool encrypt = 1;
  optional bool sign = 2;
}

message KeyAuthorizationSecret {
  optional KeyAuthorizationSecretUsage usage = 1;
  optional bytes symmetric_key = 2;
  optional bytes public_key = 3;
  // Indicates if the symmetric_key is wrapped.
  optional bool wrapped = 4 [default=false];
}

message KeyAuthorizationData {
  enum KeyAuthorizationType {
    KEY_AUTHORIZATION_TYPE_HMACSHA256 = 0;
    KEY_AUTHORIZATION_TYPE_AES256CBC_HMACSHA256 = 1;
  }
  optional KeyAuthorizationType type = 1;
  repeated KeyAuthorizationSecret secrets = 2;
}

// Software-enforced privileges.
message KeyPrivileges {
  // Allows the key to mount the cryptohome.
  optional bool mount = 1 [default=true];
  // Allows new keys to be added.
  optional bool add = 2 [default=true];
  // Allows other existing keys to be removed.
  optional bool remove = 3 [default=true];
  // Allows the key to update itself.
  optional bool update = 4 [default=true];
  // Allows a key to update itself iff the requested change
  // is authorized as per KeyAuthorizationData.
  optional bool authorized_update = 5 [default=false];
}

// Public metadata stored on behalf of the KeyProvider.
message KeyProviderData {
  message Entry {
    optional string name = 1;
    optional int64 number = 2;
    optional bytes bytes = 3;
  }
  repeated Entry entry = 1;
}

// Cryptographic signature algorithm type for challenge requests. Used with
// challenge-response cryptohome keys.
enum ChallengeSignatureAlgorithm {
  CHALLENGE_RSASSA_PKCS1_V1_5_SHA1 = 1;
  CHALLENGE_RSASSA_PKCS1_V1_5_SHA256 = 2;
  CHALLENGE_RSASSA_PKCS1_V1_5_SHA384 = 3;
  CHALLENGE_RSASSA_PKCS1_V1_5_SHA512 = 4;
}

// Description of a public key of an asymmetric cryptographic key. Used with
// challenge-response cryptohome keys.
message ChallengePublicKeyInfo {
  // DER-encoded blob of the X.509 Subject Public Key Info.
  optional bytes public_key_spki_der = 1;
  // Supported signature algorithms, in the order of preference (starting from
  // the most preferred). Absence of this field denotes that the key cannot be
  // used for signing.
  repeated ChallengeSignatureAlgorithm signature_algorithm = 2;
}

// Policies which determine how a key can be used. |GetSupportedKeyPolicies|
// request can be used to determine if a given policy value is supported.
// This message is also used inside of |GetKeyDataReply|, which allows clients
// to query current key state without submitting an authentication attempt.
message KeyPolicy {
  // Is this key additionally protected from brute force attacks as a low
  // entropy credential? For such keys, delays between subsequent unsuccessful
  // authorization attempts and/or a limit on the number of such attempts are
  // enforced to slow down dictionary-based attacks. Set this to true when
  // registering a key to protect it.
  optional bool low_entropy_credential = 1;
  // If true, the key is "locked" after too many unsuccessful authorization
  // attempts. Future authentication attempts against a locked key fail with
  // CRYPTOHOME_ERROR_TPM_DEFEND_LOCK error.
  // Currently, such locking is supported only for keys with
  // |low_entropy_credential| policy set to true,
  // This field is ignored when registering a new key.
  optional bool auth_locked = 2;
}

// Non-secret data describing the key.
message KeyData {
  // The KeyType should specify the handling needed by Cryptohome
  // and not a provider KeyType.
  enum KeyType {
    // Password-based key. The password's text or its hashed/transformed
    // representation is transmitted in the |secret| field of the Key message.
    KEY_TYPE_PASSWORD = 0;
    // The challenge-response type of key. The secret data for such key is not
    // passed clear-text through D-Bus calls, but is instead handled by
    // cryptohome internally. In order to authenticate using such key,
    // cryptohome will issue one or multiple challenge requests.
    KEY_TYPE_CHALLENGE_RESPONSE = 1;
  }
  optional KeyType type = 1;
  // All keys must be labeled when persisted to disk, but when KeyData
  // is used in an UpdateKeyRequest, only defined fields are necessary
  // (so that the caller doesn't need the full KeyData first).
  optional string label = 2;
  // If undefined, use the default settings.
  optional KeyPrivileges privileges = 3;
  optional int64 revision = 4;
  // At present, only support for one authorization mechanism is implemented.
  repeated KeyAuthorizationData authorization_data = 5;
  // Data stored for use by the provider of the key, often for pre-processing
  // of passwords or custom provider key typing.
  // This will be size-limited by serialized size (e.g., 4096 bytes).
  optional KeyProviderData provider_data = 6;
  // Is set when |type| is |KEY_TYPE_CHALLENGE_RESPONSE|. Specifies the list of
  // keys that should be used for challenge requests.
  repeated ChallengePublicKeyInfo challenge_response_key = 7;
  // Optional additional policy to apply to the key. Certain policy values
  // require hardware support which may not be available.
  optional KeyPolicy policy = 8;
}

// Key is not presently persisted to disk, but it acts as the single authority
// for what comprises a key.
message Key {
  // In most cases, |data| is required.  When used in an UpdateKeyRequest, it
  // is only required if KeyData is changing.  If only the |secret| is changing,
  // this field may be left unset.
  optional KeyData data = 1;
  // |secret| is required for many requests, like AddKeyRequest, but not all.
  // An UpdateKeyRequest only requires the changes to the Key that was
  // was authorized in the AuthorizationRequest. Making |secret| required would
  // logically force a key rotation even if the values were the same.
  optional bytes secret = 2;
}