1 /* 2 * Copyright 2015 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 #ifndef GATEKEEPER_H_ 18 #define GATEKEEPER_H_ 19 20 #include <stdint.h> 21 #include <UniquePtr.h> 22 #include <hardware/hw_auth_token.h> 23 24 #include "gatekeeper_messages.h" 25 #include "password_handle.h" 26 27 namespace gatekeeper { 28 29 struct __attribute__((packed)) failure_record_t { 30 uint64_t secure_user_id; 31 uint64_t last_checked_timestamp; 32 uint32_t failure_counter; 33 }; 34 35 /** 36 * Base class for gatekeeper implementations. Provides all functionality except 37 * the ability to create/access keys and compute signatures. These are left up 38 * to the platform-specific implementation. 39 */ 40 class GateKeeper { 41 public: 42 GateKeeper() {} 43 virtual ~GateKeeper() {} 44 45 void Enroll(const EnrollRequest &request, EnrollResponse *response); 46 void Verify(const VerifyRequest &request, VerifyResponse *response); 47 48 protected: 49 50 // The following methods are intended to be implemented by concrete subclasses 51 52 /** 53 * Retrieves the key used by GateKeeper::MintAuthToken to sign the payload 54 * of the AuthToken. This is not cached as is may have changed due to an event such 55 * as a password change. 56 * 57 * Writes the length in bytes of the returned key to length if it is not null. 58 * 59 * Ownership of the auth_token_key pointer is maintained by the implementor. 60 * 61 * Returns true if the key was successfully fetched. 62 * 63 */ 64 virtual bool GetAuthTokenKey(const uint8_t **auth_token_key, uint32_t *length) 65 const = 0; 66 67 /** 68 * The key used to sign and verify password data. 69 * 70 * MUST be different from the AuthTokenKey. 71 * 72 * GetPasswordKey is not const because unlike AuthTokenKey, 73 * this value can be cached. 74 * 75 * Ownership of the password_key pointer is maintained by the implementor. 76 * 77 */ 78 virtual void GetPasswordKey(const uint8_t **password_key, uint32_t *length) = 0; 79 80 /** 81 * Uses platform-specific routines to compute a signature on the provided password. 82 * 83 * This can be implemented as a simple pass-through to ComputeSignature, but is 84 * available in case handling for password signatures is different from general 85 * purpose signatures. 86 * 87 * Writes the signature_length size signature to the 'signature' pointer. 88 */ 89 virtual void ComputePasswordSignature(uint8_t *signature, uint32_t signature_length, 90 const uint8_t *key, uint32_t key_length, const uint8_t *password, 91 uint32_t password_length, salt_t salt) const = 0; 92 93 /** 94 * Retrieves a unique, cryptographically randomly generated buffer for use in password 95 * hashing, etc. 96 * 97 * Assings the random to the random UniquePtr, relinquishing ownership to the caller 98 */ 99 virtual void GetRandom(void *random, uint32_t requested_size) const = 0; 100 101 /** 102 * Uses platform-specific routines to compute a signature on the provided message. 103 * 104 * Writes the signature_length size signature to the 'signature' pointer. 105 */ 106 virtual void ComputeSignature(uint8_t *signature, uint32_t signature_length, 107 const uint8_t *key, uint32_t key_length, const uint8_t *message, 108 const uint32_t length) const = 0; 109 110 /** 111 * Get the time since boot in milliseconds. 112 * 113 * Should return 0 on error. 114 */ 115 virtual uint64_t GetMillisecondsSinceBoot() const = 0; 116 117 /** 118 * Returns the value of the current failure record for the user. 119 * 120 * The failure record should be written to hardware-backed secure storage, such as 121 * RPMB, if the target device supports it. 122 * 123 * If 'secure' is false, password is operating in a fallback mode. Implementations 124 * may store the failure record in memory or in non-secure storage if this value is false. 125 * 126 * Returns true on success, false if failure record cannot be retrieved. 127 */ 128 virtual bool GetFailureRecord(uint32_t uid, secure_id_t user_id, failure_record_t *record, 129 bool secure) = 0; 130 131 /** 132 * Initializes or reinitializes the failure record for the current user. 133 * 134 * Must be persisted in secure storage if the target device supports it. 135 * 136 * If 'secure' is false, password is operating in a fallback mode. Implementations 137 * may store the failure record in memory or in non-secure storage if this value is false. 138 * 139 * Returns true if the failure record was successfully persisted. 140 */ 141 virtual bool ClearFailureRecord(uint32_t uid, secure_id_t user_id, bool secure) = 0; 142 143 /* 144 * Writes the provided failure record to persistent storage. 145 * 146 * Must be persisted in secure storage if the target device supports it. 147 * 148 * If 'secure' is false, password is operating in a fallback mode. Implementations 149 * may store the failure record in memory or in non-secure storage if this value is false. 150 * 151 * Returns true if record was successfully written. 152 */ 153 virtual bool WriteFailureRecord(uint32_t uid, failure_record_t *record, bool secure) = 0; 154 155 /** 156 * Computes the amount of time to throttle the user due to the current failure_record 157 * counter. An implementation is provided by the generic GateKeeper, but may be 158 * overriden. 159 */ 160 virtual uint32_t ComputeRetryTimeout(const failure_record_t *record); 161 162 /** 163 * Returns whether the GateKeeper implementation is backed by hardware. 164 */ 165 virtual bool IsHardwareBacked() const = 0; 166 167 /** 168 * Verifies that handle matches password HMAC'ed with the password_key 169 */ 170 virtual bool DoVerify(const password_handle_t *expected_handle, const SizedBuffer &password); 171 172 private: 173 /** 174 * Generates a signed attestation of an authentication event and assings 175 * to auth_token UniquePtr. 176 * The format is consistent with that of hw_auth_token_t. 177 * Also returns the length in length if it is not null. 178 */ 179 void MintAuthToken(UniquePtr<uint8_t> *auth_token, uint32_t *length, uint64_t timestamp, 180 secure_id_t user_id, secure_id_t authenticator_id, uint64_t challenge); 181 182 /** 183 * Populates password_handle with the data provided and computes HMAC. 184 */ 185 bool CreatePasswordHandle(SizedBuffer *password_handle, salt_t salt, 186 secure_id_t secure_id, secure_id_t authenticator_id, uint8_t handle_version, 187 const uint8_t *password, uint32_t password_length); 188 189 /** 190 * Increments the counter on the current failure record for the provided user id. 191 * Sets the last_checked_timestamp to timestamp. Writes the updated record 192 * to *record if not null. 193 * 194 * Returns true if failure record was successfully incremented. 195 */ 196 bool IncrementFailureRecord(uint32_t uid, secure_id_t user_id, uint64_t timestamp, 197 failure_record_t *record, bool secure); 198 199 /** 200 * Determines whether the request is within the current throttle window. 201 * 202 * If the system timer has been reset due to a reboot or otherwise, resets 203 * the throttle window with a base at the current time. 204 * 205 * Returns true if the request is in the throttle window. 206 */ 207 bool ThrottleRequest(uint32_t uid, uint64_t timestamp, 208 failure_record_t *record, bool secure, GateKeeperMessage *response); 209 }; 210 211 } 212 213 #endif // GATEKEEPER_H_ 214
