cryptohome/flatbuffer_schemas/structures.fbs

// Copyright 2021 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

include "libhwsec/structures/signature_sealed_data.fbs";

// Our Python generator removes the "_serialized_" namespace when generating
// the code, to avoid symbol clash with the code generated by flatc.
namespace cryptohome._serialized_;

// Defined the attributes that may be used in this schema file.
attribute "optional";
attribute "secure";
attribute "serializable";

// Cryptographic signature algorithm type for challenge requests. Used with
// challenge-response cryptohome keys.
enum SerializedChallengeSignatureAlgorithm : int {
  kRsassaPkcs1V15Sha1 = 1,
  kRsassaPkcs1V15Sha256 = 2,
  kRsassaPkcs1V15Sha384 = 3,
  kRsassaPkcs1V15Sha512 = 4,
}

// Fields specific to the challenge-response protection.
// The Scrypt KDF passphrase, used for the protection of the keyset, is
// defined as a concatenation of two values:
// * The first is the blob which is sealed in |sealed_secret|.
// * The second is the deterministic signature of |salt| using the
//   |salt_signature_algorithm| algorithm.
// The cryptographic key specified in |public_key_spki_der| is used for both.
table SerializedSignatureChallengeInfo (serializable) {
  // DER-encoded blob of the X.509 Subject Public Key Info of the key to be
  // challenged in order to obtain the KDF passphrase for decrypting the vault
  // keyset.
  public_key_spki_der:[ubyte] (id: 0);
  // Container with the secret data which is sealed using the TPM in a way
  // that the process of its unsealing involves signature challenges against
  // the specified key. This secret data is one of the sources for building
  // the KDF passphrase.
  sealed_secret:hwsec._serialized_.SignatureSealedData (id: 2);
  // Salt whose signature is another source for building the KDF passphrase.
  salt:[ubyte] (id: 3);
  // Signature algorithm to be used for signing |salt|.
  // NOTE: the signature algorithm has to be deterministic (that is, always
  // produce the same output for the same input).
  salt_signature_algorithm:SerializedChallengeSignatureAlgorithm = null (id: 4);
}

// Description of a public key of an asymmetric cryptographic key. Used with
// challenge-response cryptohome keys.
table SerializedChallengePublicKeyInfo {
  // DER-encoded blob of the X.509 Subject Public Key Info.
  public_key_spki_der:[ubyte] (id: 0);
  // 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.
  signature_algorithm:[SerializedChallengeSignatureAlgorithm] (id: 1);
}

root_type SerializedSignatureChallengeInfo;