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// Copyright 2024 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef CRYPTO_USER_VERIFYING_KEY_H_
#define CRYPTO_USER_VERIFYING_KEY_H_
#include <memory>
#include <optional>
#include <string>
#include <variant>
#include <vector>
#include "base/containers/span.h"
#include "base/functional/callback.h"
#include "base/memory/ref_counted.h"
#include "base/types/expected.h"
#include "build/build_config.h"
#include "crypto/crypto_export.h"
#include "crypto/scoped_lacontext.h"
#include "crypto/signature_verifier.h"
#include "crypto/unexportable_key.h"
namespace crypto {
typedef std::string UserVerifyingKeyLabel;
// Error values supplied to the callbacks for creating and retrieving
// user-verifying keys, upon failure.
enum class UserVerifyingKeyCreationError {
kPlatformApiError = 0,
kDuplicateCredential = 1,
kNotFound = 2,
kUserCancellation = 3,
kNoMatchingAlgorithm = 4,
kUnknownError = 5,
};
// Error values supplied to the callback for signing with a user-verifying key,
// upon failure.
enum class UserVerifyingKeySigningError {
kPlatformApiError = 0,
kUserCancellation = 1,
kUnknownError = 2,
};
// UserVerifyingSigningKey is a hardware-backed key that triggers a user
// verification by the platform before a signature will be provided.
//
// Notes:
// - This is currently only supported on Windows and Mac.
// - This does not export a wrapped key because the Windows implementation uses
// the WinRT KeyCredentialManager which addresses stored keys by name.
// - The interface for this class will likely need to be generalized as support
// for other platforms is added.
class CRYPTO_EXPORT UserVerifyingSigningKey {
public:
virtual ~UserVerifyingSigningKey();
using UserVerifyingKeySignatureCallback = base::OnceCallback<void(
base::expected<std::vector<uint8_t>, UserVerifyingKeySigningError>)>;
// Sign invokes |callback| to provide a signature of |data|, or |nullopt| if
// an error occurs during signing.
virtual void Sign(base::span<const uint8_t> data,
UserVerifyingKeySignatureCallback callback) = 0;
// Provides the SPKI public key.
virtual std::vector<uint8_t> GetPublicKey() const = 0;
// Get a reference to the label used to create or retrieve this key.
virtual const UserVerifyingKeyLabel& GetKeyLabel() const = 0;
// Returns true if the underlying key is stored in "hardware". Something like
// ARM TrustZone would count as hardware for these purposes.
virtual bool IsHardwareBacked() const;
};
// Reference-counted wrapper for UserVeriyingSigningKey.
class CRYPTO_EXPORT RefCountedUserVerifyingSigningKey
: public base::RefCountedThreadSafe<RefCountedUserVerifyingSigningKey> {
public:
explicit RefCountedUserVerifyingSigningKey(
std::unique_ptr<crypto::UserVerifyingSigningKey> key);
RefCountedUserVerifyingSigningKey(const RefCountedUserVerifyingSigningKey&) =
delete;
RefCountedUserVerifyingSigningKey& operator=(
const RefCountedUserVerifyingSigningKey&) = delete;
crypto::UserVerifyingSigningKey& key() const { return *key_; }
private:
friend class base::RefCountedThreadSafe<RefCountedUserVerifyingSigningKey>;
~RefCountedUserVerifyingSigningKey();
const std::unique_ptr<crypto::UserVerifyingSigningKey> key_;
};
// UserVerifyingKeyProvider creates |UserVerifyingSigningKey|s.
class CRYPTO_EXPORT UserVerifyingKeyProvider {
public:
struct CRYPTO_EXPORT Config {
Config();
Config(const Config& config) = delete;
Config& operator=(const Config& config) = delete;
Config(Config&& config);
Config& operator=(Config&& config);
~Config();
#if BUILDFLAG(IS_MAC)
// The keychain access group the key is shared with. The binary must be
// codesigned with the corresponding entitlement.
// https://developer.apple.com/documentation/bundleresources/entitlements/keychain-access-groups?language=objc
// This must be set to a non empty value when using user verifying keys on
// macOS.
std::string keychain_access_group;
// Optional LAContext to be used when retrieving and storing keys. Passing
// an authenticated LAContext lets you call UserVerifyingSigningKey::Sign()
// without triggering a macOS local authentication prompt.
std::optional<ScopedLAContext> lacontext;
#endif // BUILDFLAG(IS_MAC)
};
using UserVerifyingKeyCreationCallback = base::OnceCallback<void(
base::expected<std::unique_ptr<UserVerifyingSigningKey>,
UserVerifyingKeyCreationError>)>;
virtual ~UserVerifyingKeyProvider();
// Similar to |GenerateSigningKeySlowly| but the resulting signing key can
// only be used with a local user authentication by the platform. This can be
// called from any thread as the work is done asynchronously on a
// high-priority thread when the underlying platform is slow.
// Invokes |callback| with the resulting key, or nullptr on error.
virtual void GenerateUserVerifyingSigningKey(
base::span<const SignatureVerifier::SignatureAlgorithm>
acceptable_algorithms,
UserVerifyingKeyCreationCallback callback) = 0;
// Similar to |FromWrappedSigningKey| but uses a wrapped key that was
// generated from |GenerateUserVerifyingSigningKey|. This can be called from
// any thread as the work is done asynchronously on a high-priority thread
// when the underlying platform is slow.
// Invokes |callback| with the resulting key, or nullptr on error.
virtual void GetUserVerifyingSigningKey(
UserVerifyingKeyLabel key_label,
UserVerifyingKeyCreationCallback callback) = 0;
// Deletes a user verifying signing key. Work is be done asynchronously on a
// low-priority thread when the underlying platform is slow.
// Invokes |callback| with `true` if the key was found and deleted, `false`
// otherwise.
virtual void DeleteUserVerifyingKey(
UserVerifyingKeyLabel key_label,
base::OnceCallback<void(bool)> callback) = 0;
};
// GetUserVerifyingKeyProvider returns |UserVerifyingKeyProvider| for the
// current platform, or nullptr if this is not implemented on the current
// platform.
// Note that this will return non null if keys are supported but not available,
// i.e. if |AreUserVerifyingKeysSupported| returns false. In that case,
// operations would fail.
CRYPTO_EXPORT std::unique_ptr<UserVerifyingKeyProvider>
GetUserVerifyingKeyProvider(UserVerifyingKeyProvider::Config config);
// Invokes the callback with true if UV keys can be used on the current
// platform, and false otherwise. `callback` can be invoked synchronously or
// asynchronously.
CRYPTO_EXPORT void AreUserVerifyingKeysSupported(
UserVerifyingKeyProvider::Config config,
base::OnceCallback<void(bool)> callback);
namespace internal {
CRYPTO_EXPORT void SetUserVerifyingKeyProviderForTesting(
std::unique_ptr<UserVerifyingKeyProvider> (*func)());
} // namespace internal
} // namespace crypto
#endif // CRYPTO_USER_VERIFYING_KEY_H_
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