device/fido/attested_credential_data.cc

// Copyright 2017 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "device/fido/attested_credential_data.h"

#include <algorithm>
#include <utility>

#include "base/containers/extend.h"
#include "base/containers/span_reader.h"
#include "base/containers/to_array.h"
#include "base/containers/to_vector.h"
#include "base/numerics/safe_math.h"
#include "components/cbor/reader.h"
#include "components/device_event_log/device_event_log.h"
#include "device/fido/public/fido_constants.h"
#include "device/fido/public_key.h"

namespace device {

// static
std::optional<std::pair<AttestedCredentialData, base::span<const uint8_t>>>
AttestedCredentialData::ConsumeFromCtapResponse(
    base::span<const uint8_t> buffer) {
  if (buffer.size() < kAaguidLength) {
    return std::nullopt;
  }

  auto aaguid = buffer.first<kAaguidLength>();
  buffer = buffer.subspan(kAaguidLength);

  if (buffer.size() < kCredentialIdLengthLength) {
    return std::nullopt;
  }

  auto credential_id_length_span = buffer.first<kCredentialIdLengthLength>();
  const size_t credential_id_length =
      (base::strict_cast<size_t>(credential_id_length_span[0]) << 8) |
      base::strict_cast<size_t>(credential_id_length_span[1]);
  buffer = buffer.subspan(kCredentialIdLengthLength);

  if (buffer.size() < credential_id_length) {
    return std::nullopt;
  }

  auto credential_id = buffer.first(credential_id_length);
  buffer = buffer.subspan(credential_id_length);

  size_t public_key_byte_len;
  std::optional<cbor::Value> public_key_cbor =
      cbor::Reader::Read(buffer, &public_key_byte_len);
  if (!public_key_cbor || !public_key_cbor->is_map()) {
    FIDO_LOG(ERROR) << "CBOR error in COSE public key";
    return std::nullopt;
  }

  const base::span<const uint8_t> public_key_cbor_bytes(
      buffer.first(public_key_byte_len));
  buffer = buffer.subspan(public_key_byte_len);

  const cbor::Value::MapValue& public_key_map = public_key_cbor->GetMap();

  // kAlg is required to be present. See
  // https://www.w3.org/TR/webauthn/#credentialpublickey
  // COSE allows it to be a string or an integer. However, WebAuthn defines
  // COSEAlgorithmIdentifier to be a long[1], thus only integer-based
  // algorithms can be negotiated.
  //
  // [1] https://www.w3.org/TR/webauthn/#alg-identifier
  const auto alg_it =
      public_key_map.find(cbor::Value(static_cast<int64_t>(CoseKeyKey::kAlg)));
  if (alg_it == public_key_map.end() || !alg_it->second.is_integer()) {
    FIDO_LOG(ERROR) << "Failed to parse COSE key algorithm";
    return std::nullopt;
  }

  // kKty is required in COSE keys:
  // https://tools.ietf.org/html/rfc8152#section-7
  if (const auto kty_it = public_key_map.find(
          cbor::Value(static_cast<int64_t>(CoseKeyKey::kKty)));
      kty_it == public_key_map.end() || !kty_it->second.is_integer()) {
    FIDO_LOG(ERROR) << "Failed to parse COSE key type";
    return std::nullopt;
  }

  // In WebIDL, a |long| is an |int32_t|[1].
  //
  // [1] https://heycam.github.io/webidl/#idl-long
  const int64_t algorithm64 = alg_it->second.GetInteger();
  if (algorithm64 > std::numeric_limits<int32_t>::max() ||
      algorithm64 < std::numeric_limits<int32_t>::min()) {
    FIDO_LOG(ERROR) << "COSE algorithm in public key is out of range";
    return std::nullopt;
  }
  const int32_t algorithm = static_cast<int32_t>(algorithm64);

  std::unique_ptr<PublicKey> public_key =
      PublicKey::FromCOSEKey(algorithm, public_key_cbor_bytes, public_key_map);
  if (!public_key) {
    return std::nullopt;
  }

  return std::make_pair(
      AttestedCredentialData(aaguid, credential_id_length_span,
                             base::ToVector(credential_id),
                             std::move(public_key)),
      buffer);
}

// static
std::optional<AttestedCredentialData>
AttestedCredentialData::CreateFromU2fRegisterResponse(
    base::span<const uint8_t> u2f_data,
    std::unique_ptr<PublicKey> public_key) {
  // TODO(crbug.com/41363164): Introduce a CredentialID class to do this
  // extraction. Extract the length of the credential (i.e. of the U2FResponse
  // key handle). Length is big endian.
  base::SpanReader<const uint8_t> reader(u2f_data);
  reader.Skip(kU2fKeyHandleLengthOffset);
  uint8_t extracted_length;
  if (!reader.ReadU8BigEndian(extracted_length)) {
    return std::nullopt;
  }

  // For U2F register request, device AAGUID is set to zeros.
  std::array<uint8_t, kAaguidLength> aaguid = {};

  // Note that U2F responses only use one byte for length.
  std::array<uint8_t, kCredentialIdLengthLength> credential_id_length = {
      0, extracted_length};

  // Extract the credential id (i.e. key handle).
  std::optional<base::span<const uint8_t>> credential_id =
      reader.Read(extracted_length);

  if (!credential_id.has_value()) {
    return std::nullopt;
  }

  return AttestedCredentialData(aaguid, credential_id_length,
                                base::ToVector(*credential_id),
                                std::move(public_key));
}

AttestedCredentialData::AttestedCredentialData(AttestedCredentialData&& other) =
    default;

AttestedCredentialData::AttestedCredentialData(
    base::span<const uint8_t, kAaguidLength> aaguid,
    base::span<const uint8_t, kCredentialIdLengthLength>
        credential_id_length_bytes,
    std::vector<uint8_t> credential_id,
    std::unique_ptr<PublicKey> public_key)
    : aaguid_(base::ToArray(aaguid)),
      credential_id_length_(base::ToArray(credential_id_length_bytes)),
      credential_id_(std::move(credential_id)),
      public_key_(std::move(public_key)) {
  const size_t credential_id_length =
      (base::strict_cast<size_t>(credential_id_length_[0]) << 8) |
      base::strict_cast<size_t>(credential_id_length_[1]);
  CHECK_EQ(credential_id_length, credential_id_.size());
}

AttestedCredentialData::AttestedCredentialData(
    base::span<const uint8_t, kAaguidLength> aaguid,
    base::span<const uint8_t> credential_id,
    std::unique_ptr<PublicKey> public_key)
    : AttestedCredentialData(
          aaguid,
          std::array<uint8_t, kCredentialIdLengthLength>{
              base::checked_cast<uint8_t>((0xff00 & credential_id.size()) >> 8),
              base::checked_cast<uint8_t>(0xff & credential_id.size())},
          base::ToVector(credential_id),
          std::move(public_key)) {
  CHECK_LE(credential_id.size(), 0xffffu);
}

AttestedCredentialData& AttestedCredentialData::operator=(
    AttestedCredentialData&& other) = default;

AttestedCredentialData::~AttestedCredentialData() = default;

bool AttestedCredentialData::IsAaguidZero() const {
  return std::ranges::all_of(aaguid_, [](uint8_t v) { return v == 0; });
}

bool AttestedCredentialData::DeleteAaguid() {
  if (IsAaguidZero()) {
    return false;
  }
  std::fill(aaguid_.begin(), aaguid_.end(), 0);
  return true;
}

std::vector<uint8_t> AttestedCredentialData::SerializeAsBytes() const {
  std::vector<uint8_t> attestation_data;
  base::Extend(attestation_data, aaguid_);
  base::Extend(attestation_data, credential_id_length_);
  base::Extend(attestation_data, credential_id_);
  base::Extend(attestation_data, public_key_->cose_key_bytes);
  return attestation_data;
}

const PublicKey* AttestedCredentialData::public_key() const {
  return public_key_.get();
}

}  // namespace device