Mbed OS Reference | SecurityManager.h Source File

 /* mbed Microcontroller Library
  * Copyright (c) 2006-2020 ARM Limited
  *
  * SPDX-License-Identifier: Apache-2.0
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *     http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
 
 #ifndef BLE_SECURITY_MANAGER_H_
 #define BLE_SECURITY_MANAGER_H_
 
 #include <cstdint>
 
 #include "ble/common/BLETypes.h"
 #include "ble/common/blecommon.h"
 #include "ble/common/CallChainOfFunctionPointersWithContext.h"
 
 namespace ble {
 
 #if !defined(DOXYGEN_ONLY)
 namespace impl {
 class SecurityManager;
 }
 #endif // !defined(DOXYGEN_ONLY)
 
 /**
  * Overview
  *
  * Security Manager is used to provide link security through encryption, signing and authentication
  * which are made possible by pairing and optionally bonding. Pairing is the process of establishing
  * and/or exchanging keys used for the current connection. Bonding means saving this information so that
  * it can later be used after reconnecting without having to pair again. This saves time and power.
  *
  * @par Paring
  *
  * There are several ways to provide different levels of security during pairing depending on your requirements
  * and the facilities provided by the application. The process starts with initialising the SecurityManager
  * with default options for new connections. Some settings can later be changed per link or globally.
  *
  * The important settings in the init() function are the MITM requirement and IO capabilities. Man in the
  * Middle (MITM) protection prevents an attack where one device can impersonate another device by
  * pairing with both devices at the same time. This protection is achieved by sharing some information
  * between the devices through some independent channel. The IO capabilities of both devices dictate
  * what algorithm is used. For details @see BLUETOOTH SPECIFICATION Version 5.0 | Vol 3, Part H - 2.3.5.1.
  * You can change the IO capabilities after initialisation with setIoCapability(). This will take effect
  * for all subsequent pairings.
  *
  * @par Out of Band data used in pairing
  *
  * Sharing this information through IO capabilities means user interaction which limits the degree of
  * protection due to the limit of the amount of data that we can expect the user to transfer. Another
  * solution is using OOB (out of band) communication to transfer this data instead which can send much
  * more data making MITM attack even less likely to succeed. OOB data has to be exchanged by the application
  * and provided to the Security Manager. Use setOOBDataUsage() to indicate you want to use it. The same call also
  * allows you to set whether or not the communication channel you are using to transmit the OOB data is
  * itself secure against MITM protection - this will set the level of the link security achieved using pairing
  * that uses this data.
  *
  * The most secure pairing is provided by Secure Connections which relies on Elliptical Curve Cryptography.
  * Support for Secure Connections is dependent on both the stack and controller on both sides supporting
  * it. If either side doesn't support it Legacy Pairing will be used. This is an older standard of pairing.
  * If higher security is required legacy pairing can be disabled by calling allowLegacyPairing(false);
  *
  * @par Signing
  *
  * Applications may require a level of security providing confidence that data transfers are coming
  * from a trusted source. This can be achieved by encrypting the link which also provides added confidentiality.
  * Encryption is a good choice when a device stays connected but introduces latency due to the need of encrypting the
  * link if the device only connects periodically to transfer data. If confidentiality is not required data GATT
  * server may allow writes to happen over an unencrypted link but authenticated by a signature present in each packet.
  * This signature relies on having sent a signing key to the peer during pairing prior to sending any signed packets.
  *
  * @par Persistence of Security information
  *
  * Security Manager stores all the data required for its operation on active links. Depending on resources
  * available on the device it will also attempt to store data for disconnected devices which have bonded to be
  * reused when reconnected.
  *
  * If the application has initialised a filesystem and the Security Manager has been provided with a
  * filepath during the init() call it may also provide data persistence across resets. This must be enabled by
  * calling preserveBondingStateOnReset(). Persistence is not guaranteed and may fail if abnormally terminated.
  * The Security Manager may also fall back to a non-persistent implementation if the resources are too limited.
  *
  * @par How to use
  *
  * First thing you need to do is to initialise the manager by calling init() with your chosen settings.
  *
  * The SecurityManager communicates with your application through events. These will trigger calls in
  * the EventHandler which you must provide by calling the setSecurityManagerEventHandler() function.
  *
  * The most important process is pairing. This may be triggered manually by calling requestPairing() or
  * may be called as a result of the application requiring encryption by calling setLinkEncryption() or
  * as a result of the application requiring MITM protection through requestAuthentication().
  *
  * All these can be implicitly called by using setLinkSecurity() to conveniently set the required
  * security for the link. The SecurityManager will trigger all the process required to achieve the set
  * security level. Security level can only be escalated. Asking the Security Manager for a lower
  * security level than the existing one will not fail but will result in a event informing the
  * application through linkEncryptionResult() of the current level (which remains unchanged).
  *
  * Depending on the IO capabilities and OOB usage settings different pairing algorithms will be chosen.
  * They will produce appropriate events which must be handled by your EventHandler. If your event handler
  * doesn't support all the calls you must not set IO capabilities or set OOB usage in such a way that would
  * trigger them or else the pairing will fail (usually by timing out).
  *
  * The simplest example is a pairing of a device with no IO capabilities and no OOB data available.
  * With such limited pairing capabilities the "just works" method will be employed. This does not provide
  * any MITM protection. The pairing (triggered implicitly or called explicitly) will result in an event
  * being generated on the peer calling pairingRequest(). The event handler must make a decision (either in
  * the application itself or based on user interaction) whether to accept the pairing and call
  * accetPairing() or cancelPairing(). The result will be communicated on both peers through an event calling
  * pairingResult() in the EventHandler.
  *
  * @par Sequence diagrams
  *
  * Sequence diagram "Just Works" pairing
  *
  * \verbatim
  *  /-------- Device 1 ---------\  *----- BLE link -----*  /----------- Device 2-----------\
  *
  * App  EventHandler      SecurityManager            SecurityManager    EventHandler      App
  *  |        |                  |                          |                 |             |
  *  |-------------------> requestPairing()                 |                 |             |
  *  |        |                  |-----[pairing start]----->|                 |             |
  *  |        |                  |                          |---------> pairingRequest() -->|
  *  |        |                  |                   acceptPairing() <--------------------- |
  *  |        |                  |<--[pairing complete]---->|                 |             |
  *  |<- pairingResult() <-------|                          |---------> pairingResult() --->|
  *  |        |                  |                          |                 |             |
  * @endverbatim
  *
  *  @note the requestPairing() call isn't required to trigger pairing. Pairing will also be triggered
  *  if you request encryption and authentication and no bonding information is available. The sequence will
  *  be the same save for the lack of explicit requestPairing() call.
  *
  *
  *  Sequence diagram Encryption request when bonding information is available
  *
  * \verbatim
  *  /--------- Device 1 ---------\  *------ BLE link ------*  /--------- Device 2 ---------\
  *
  * App  EventHandler       SecurityManager              SecurityManager   EventHandler    App
  *  |       |                    |                            |                |           |
  *  |--------------------> setLinkEncryption()                |                |           |
  *  |       |                    |<-[encryption established]->|                |           |
  *  |<- linkEncryptionResult() <-|                            |-> linkEncryptionResult() ->|
  *  |       |                    |                            |                |           |
  * @endverbatim
  *
  * @note if bonding information is not available, pairing will be triggered
  *
  *
  * Sequence diagram for Secure Connections passkey entry pairing with one device having a display only
  * and other a keyboard
  *
  * \verbatim
  *  /---- Device 1 (keyboard) ---\  *------ BLE link ------*  /----- Device 2 (display) ---\
  *
  * App  EventHandler       SecurityManager              SecurityManager  EventHandler     App
  *  |       |                    |                            |               |            |
  *  |--------------------> requestPairing()                   |               |            |
  *  |        |                   |------[pairing start]------>|               |            |
  *  |        |                   |                            |-------> pairingRequest() ->|
  *  |        |                   |                        acceptPairing() <--------------- |
  *  |        |                   |<---[secure con. pairing]-->|               |            |
  *  |<- passkeyRequest() <-------|                            |-------> passkeyDisplay() ->|
  *  |        |                   |                            |               |            |
  *
  *                  user reads the passkey on Device 2 and inputs it on Device 1
  *
  *  |        |                   |                            |               |            |
  *  |------------------->passkeyEntered()                     |               |            |
  *  |        |                   |<---[pairing complete]----->|               |            |
  *  |<- pairingResult() <--------|                            |-------> pairingResult() -->|
  *  |        |                   |                            |               |            |
  * @endverbatim
  *
  */
 class SecurityManager
 {
 public:
     /** level of security required from the link by the application */
     enum SecurityMode_t {
         SECURITY_MODE_NO_ACCESS,
         SECURITY_MODE_ENCRYPTION_OPEN_LINK, /**< Require no protection, open link. */
         SECURITY_MODE_ENCRYPTION_NO_MITM,   /**< Require encryption, but no MITM protection. */
         SECURITY_MODE_ENCRYPTION_WITH_MITM, /**< Require encryption and MITM protection. */
         SECURITY_MODE_SIGNED_NO_MITM,       /**< Require signing or encryption, but no MITM protection. */
         SECURITY_MODE_SIGNED_WITH_MITM,     /**< Require signing or encryption, and MITM protection. */
     };
 
     /** Input/output capability of the device and application */
     enum SecurityIOCapabilities_t {
         IO_CAPS_DISPLAY_ONLY = 0x00,     /**< Display only. */
         IO_CAPS_DISPLAY_YESNO = 0x01,    /**< Display and yes/no entry. */
         IO_CAPS_KEYBOARD_ONLY = 0x02,    /**< Keyboard only. */
         IO_CAPS_NONE = 0x03,             /**< No I/O capabilities. */
         IO_CAPS_KEYBOARD_DISPLAY = 0x04, /**< Keyboard and display. */
     };
 
     /** Result of security requests */
     enum SecurityCompletionStatus_t {
         SEC_STATUS_SUCCESS              = 0x00,  /**< Procedure completed with success. */
         SEC_STATUS_TIMEOUT              = 0x01,  /**< Procedure timed out. */
         SEC_STATUS_PDU_INVALID          = 0x02,  /**< Invalid PDU received. */
         SEC_STATUS_PASSKEY_ENTRY_FAILED = 0x81,  /**< Passkey entry failed (user cancelled or other). */
         SEC_STATUS_OOB_NOT_AVAILABLE    = 0x82,  /**< Out of Band Key not available. */
         SEC_STATUS_AUTH_REQ             = 0x83,  /**< Authentication requirements not met. */
         SEC_STATUS_CONFIRM_VALUE        = 0x84,  /**< Confirm value failed. */
         SEC_STATUS_PAIRING_NOT_SUPP     = 0x85,  /**< Pairing not supported.  */
         SEC_STATUS_ENC_KEY_SIZE         = 0x86,  /**< Encryption key size. */
         SEC_STATUS_SMP_CMD_UNSUPPORTED  = 0x87,  /**< Unsupported SMP command. */
         SEC_STATUS_UNSPECIFIED          = 0x88,  /**< Unspecified reason. */
         SEC_STATUS_REPEATED_ATTEMPTS    = 0x89,  /**< Too little time elapsed since last attempt. */
         SEC_STATUS_INVALID_PARAMS       = 0x8A,  /**< Invalid parameters. */
         SEC_STATUS_DHKEY_CHECK_FAILED   = 0x8B,  /**< DHKey received doesn’t match locally calculated one. */
         SEC_STATUS_COMPARISON_FAILED    = 0x8C,  /**< Values in the numeric comparison protocol do not match. */
     };
 
     /**
      * Declaration of type containing a passkey to be used during pairing. This
      * is passed into initializeSecurity() to specify a pre-programmed passkey
      * for authentication instead of generating a random one.
      */
     static const unsigned PASSKEY_LEN = 6;
     typedef uint8_t Passkey_t[PASSKEY_LEN]; /**< 6-digit passkey in ASCII ('0'-'9' digits only). */
 
     typedef FunctionPointerWithContext<const SecurityManager *> SecurityManagerShutdownCallback_t;
     typedef CallChainOfFunctionPointersWithContext<const SecurityManager *> SecurityManagerShutdownCallbackChain_t;
 
     /** The stack will use these functions to signal events to the application,
      *  subclass to override handlers. Use SecurityManager::setSecurityManagerEventHandler
      *  to set the interface implementation to be used. */
     class EventHandler {
     public:
         ////////////////////////////////////////////////////////////////////////////
         // Pairing
         //
 
 #if BLE_ROLE_PERIPHERAL
         /**
          * Request application to accept or reject pairing. Application should respond by
          * calling the appropriate function: acceptPairingRequest or cancelPairingRequest
          *
          * @param[in] connectionHandle connection connectionHandle
          */
         virtual void pairingRequest(ble::connection_handle_t connectionHandle) {
             (void)connectionHandle;
         }
 #endif // BLE_ROLE_PERIPHERAL
 
         /**
          * Indicate to the application that pairing has completed.
          *
          * @param[in] connectionHandle connection connectionHandle
          * @param[in] result result of the pairing indicating success or reason for failure
          */
         virtual void pairingResult(ble::connection_handle_t connectionHandle, SecurityCompletionStatus_t result) {
             (void)connectionHandle;
             (void)result;
         }
 
         /**
          * Indicate that a peer address has been saved by the security manager or if we are
          * bonded to the peer the identity has been retrieved from the database on connection.
          *
          * @param[in] connectionHandle Connection handle.
          * @param[in] peer_address Peer address that has been saved by the security database, NULL it not found.
          * @param[in] address_is_public Address type, true if public. Invalid if peer_address NULL.
          */
         virtual void peerIdentity(ble::connection_handle_t connectionHandle,
                                   const address_t *peer_address,
                                   bool address_is_public) {
             (void)connectionHandle;
             (void)peer_address;
             (void)address_is_public;
         }
 
         ////////////////////////////////////////////////////////////////////////////
         // Security
         //
 
         /**
          * Deliver the requested whitelist to the application.
          *
          * @param[in] whitelist pointer to the whitelist filled with entries based on bonding information
          */
         virtual void whitelistFromBondTable(::ble::whitelist_t* whitelist) {
             (void)whitelist;
         }
 
         ////////////////////////////////////////////////////////////////////////////
         // Encryption
         //
 
         /**
          * Inform the device of the encryption state of a given link.
          *
          * @param[in] connectionHandle connection connectionHandle
          * @param[in] result encryption state of the link
          */
         virtual void linkEncryptionResult(ble::connection_handle_t connectionHandle, ble::link_encryption_t result) {
             (void)connectionHandle;
             (void)result;
         }
 
         ////////////////////////////////////////////////////////////////////////////
         // MITM
         //
 
         /**
          * Display the given passkey on the local device.
          *
          * @param[in] connectionHandle connection connectionHandle
          * @param[in] passkey 6 digit passkey to be displayed
          */
 #if BLE_PASSKEY_DISPLAY_REVERSED_DIGITS_DEPRECATION
         MBED_DEPRECATED_SINCE("mbed-os-6.8.0", "This returns the passkey in reverse order. Please set the config option ble.ble-passkey-display-reversed-digits-deprecation in your mbed_app.json override section to false. This will then return the passkey in the correct order.")
 #endif // BLE_PASSKEY_DISPLAY_REVERSED_DIGITS_DEPRECATION
         virtual void passkeyDisplay(ble::connection_handle_t connectionHandle, const Passkey_t passkey) {
             (void)connectionHandle;
             (void)passkey;
         }
 
 #if BLE_FEATURE_SECURE_CONNECTIONS
         /**
          * Indicate to the application that a confirmation is required. This is used
          * when the device does not have a keyboard but has a yes/no button. The device
          * displays numbers on its display in response to passkeyDisplay and the user
          * checks if they are the same on both devices. The application should proceed
          * by supplying the confirmation using the confirmationEntered function.
          *
          * @param[in] connectionHandle connection connectionHandle
          */
         virtual void confirmationRequest(ble::connection_handle_t connectionHandle) {
             (void)connectionHandle;
         }
 #endif // BLE_FEATURE_SECURE_CONNECTIONS
 
         /**
          * Indicate to the application that a passkey is required. The application should
          * proceed by supplying the passkey through the passkeyEntered function.
          *
          * @param[in] connectionHandle connection connectionHandle
          */
         virtual void passkeyRequest(ble::connection_handle_t connectionHandle) {
             (void)connectionHandle;
         }
 
 #if BLE_FEATURE_SECURE_CONNECTIONS
         /**
          * Notify the application that a key was pressed by the peer during passkey entry.
          *
          * @param[in] connectionHandle connection connectionHandle
          * @param[in] keypress type of keypress event
          */
         virtual void keypressNotification(ble::connection_handle_t connectionHandle, ble::Keypress_t keypress) {
             (void)connectionHandle;
             (void)keypress;
         }
 #endif // BLE_FEATURE_SECURE_CONNECTIONS
 
         /**
          * Indicate to the application it needs to return legacy pairing OOB to the stack.
          *
          * @param[in] connectionHandle connection connectionHandle
          */
         virtual void legacyPairingOobRequest(ble::connection_handle_t connectionHandle) {
             (void)connectionHandle;
         }
 
         /**
          * Indicate that the application needs to send legacy pairing OOB data to the peer.
          *
          * @param[in] address address that will be used in the pairing
          * @param[in] temporaryKey temporary key to be used in legacy pairing
          */
         virtual void legacyPairingOobGenerated(const ble::address_t *address,
                                                const ble::oob_tk_t *temporaryKey) {
             (void)address;
             (void)temporaryKey;
         }
 
         /**
          * Indicate that the application needs to send secure connections OOB data to the peer.
          *
          * @param[in] address address that will be used in the pairing
          * @param[in] random random number used to generate the confirmation
          * @param[in] confirm confirmation value to be use for authentication
          *                    in secure connections pairing
          */
         virtual void oobGenerated(const ble::address_t *address,
                                   const ble::oob_lesc_value_t *random,
                                   const ble::oob_confirm_t *confirm) {
             (void)address;
             (void)random;
             (void)confirm;
         }
 
         ////////////////////////////////////////////////////////////////////////////
         // Keys
         //
 
 #if BLE_FEATURE_SIGNING
         /**
          * Deliver the signing key to the application.
          *
          * @param[in] connectionHandle connection connectionHandle
          * @param[in] csrk signing key, pointer only valid during call
          * @param[in] authenticated indicates if the signing key is authenticated
          */
         virtual void signingKey(ble::connection_handle_t connectionHandle, const ble::csrk_t *csrk, bool authenticated) {
             (void)connectionHandle;
             (void)csrk;
             (void)authenticated;
         }
 #endif // BLE_FEATURE_SIGNING
 
         /**
          * Prevent polymorphic deletion and avoid unnecessary virtual destructor
          * as the SecurityManager class will never delete the instance it contains.
          */
         ~EventHandler() = default;
     };
 
     /*
      * The following functions are meant to be overridden in the platform-specific sub-class.
      */
 public:
     ////////////////////////////////////////////////////////////////////////////
     // SM lifecycle management
     //
 
     /**
      * Enable the BLE stack's Security Manager. The Security Manager implements
      * the actual cryptographic algorithms and protocol exchanges that allow two
      * devices to securely exchange data and privately detect each other.
      * Calling this API is a prerequisite for encryption and pairing (bonding).
      *
      * @param[in]  enableBonding Allow for bonding.
      * @param[in]  requireMITM   Require protection for man-in-the-middle attacks.
      * @param[in]  iocaps        To specify the I/O capabilities of this peripheral,
      *                           such as availability of a display or keyboard, to
      *                           support out-of-band exchanges of security data.
      * @param[in]  passkey       To specify a static passkey.
      * @param[in]  signing       Generate and distribute signing key during pairing
      * @param[in]  dbFilepath    Path to the file used to store keys in the filesystem,
      *                           if NULL keys will be only stored in memory
      *
      *
      * @return BLE_ERROR_NONE on success.
      */
     ble_error_t init(
         bool                     enableBonding = true,
         bool                     requireMITM   = true,
         SecurityIOCapabilities_t iocaps        = IO_CAPS_NONE,
         const Passkey_t          passkey       = nullptr,
         bool                     signing       = true,
         const char              *dbFilepath    = nullptr
     );
 
     /**
      * Change the file used for the security database. If path is invalid or a NULL is passed
      * keys will only be stored in memory.
      *
      * @note This operation is only allowed with no active connections.
      *
      * @param[in]  dbFilepath    Path to the file used to store keys in the filesystem,
      *                           if NULL keys will be only stored in memory
      *
      * @return BLE_ERROR_NONE on success.
      */
     ble_error_t setDatabaseFilepath(const char *dbFilepath = nullptr);
 
     /**
      * Notify all registered onShutdown callbacks that the SecurityManager is
      * about to be shutdown and clear all SecurityManager state of the
      * associated object.
      *
      * This function is meant to be overridden in the platform-specific
      * sub-class. Nevertheless, the sub-class is only expected to reset its
      * state and not the data held in SecurityManager members. This shall be
      * achieved by a call to SecurityManager::reset() from the sub-class'
      * reset() implementation.
      *
      * @return BLE_ERROR_NONE on success.
      */
     ble_error_t reset();
 
     /**
      * Normally all bonding information is lost when device is reset, this requests that the stack
      * attempts to save the information and reload it during initialisation. This is not guaranteed.
      *
      * @param[in] enable if true the stack will attempt to preserve bonding information on reset.
      * @return BLE_ERROR_NONE or appropriate error code indicating the failure reason.
      */
     ble_error_t preserveBondingStateOnReset(bool enable);
 
     ////////////////////////////////////////////////////////////////////////////
     // List management
     //
 
     /**
      * Delete all peer device context and all related bonding information from
      * the database within the security manager.
      *
      * @retval BLE_ERROR_NONE             On success, else an error code indicating reason for failure.
      * @retval BLE_ERROR_INVALID_STATE    If the API is called without module initialization or
      *                                    application registration.
      */
     ble_error_t purgeAllBondingState();
 
     /**
      * Create a list of addresses from all peers in the bond table and generate
      * an event which returns it as a whitelist. Pass in the container for the whitelist.
      * This will be returned by the event.
      *
      * @param[in] whitelist Preallocated whitelist which will be filled up to its capacity.
      *                      If whitelist already contains entries this will be appended to.
      *                      Do not access the whitelist until callback has been called,
      *                      returning the filled whitelist.
      *
      * @retval BLE_ERROR_NONE On success, else an error code indicating reason for failure
      */
     ble_error_t generateWhitelistFromBondTable(::ble::whitelist_t *whitelist) const;
 
     ////////////////////////////////////////////////////////////////////////////
     // Pairing
     //
 
 #if BLE_ROLE_CENTRAL
     /**
      * Request pairing with the peer. Called by the master.
      * @note Slave can call requestAuthentication or setLinkEncryption to achieve security.
      *
      * @param[in] connectionHandle Handle to identify the connection.
      * @return BLE_ERROR_NONE or appropriate error code indicating the failure reason.
      */
     ble_error_t requestPairing(ble::connection_handle_t connectionHandle);
 #endif // BLE_ROLE_CENTRAL
 
 #if BLE_ROLE_PERIPHERAL
     /**
      * Accept the pairing request. Called as a result of pairingRequest being called
      * on the event handler.
      *
      * @param[in] connectionHandle Handle to identify the connection.
      * @return BLE_ERROR_NONE or appropriate error code indicating the failure reason.
      */
     ble_error_t acceptPairingRequest(ble::connection_handle_t connectionHandle);
 #endif // BLE_ROLE_PERIPHERAL
 
     /**
      * Reject pairing request if the local device is the slave or cancel an outstanding
      * pairing request if master.
      *
      * @param[in] connectionHandle Handle to identify the connection.
      * @return BLE_ERROR_NONE or appropriate error code indicating the failure reason.
      */
     ble_error_t cancelPairingRequest(ble::connection_handle_t connectionHandle);
 
     /**
      * Tell the stack whether the application needs to authorise pairing requests or should
      * they be automatically accepted.
      *
      * @param[in] required If set to true, pairingRequest in the event handler will
      *                     will be called and will require an action from the application
      *                     to continue with pairing by calling acceptPairingRequest
      *                     or cancelPairingRequest if the user wishes to reject it.
      * @return BLE_ERROR_NONE or appropriate error code indicating the failure reason.
      */
     ble_error_t setPairingRequestAuthorisation(bool required = true);
 
     /**
      * Retrieve identity address for the peer on the given connection.
      *
      * @param[in] connectionHandle Handle to identify the connection.
      * @return BLE_ERROR_NONE or appropriate error code indicating the failure reason.
      */
     ble_error_t getPeerIdentity(ble::connection_handle_t connectionHandle);
 
     ////////////////////////////////////////////////////////////////////////////
     // Feature support
     //
 
 #if BLE_FEATURE_SECURE_CONNECTIONS
     /**
      * Allow of disallow the use of legacy pairing in case the application only wants
      * to force the use of Secure Connections. If legacy pairing is disallowed and either
      * side doesn't support Secure Connections the pairing will fail.
      *
      * @param[out] allow If true legacy pairing will be used if either side doesn't support Secure Connections.
      * @return BLE_ERROR_NONE or appropriate error code indicating the failure reason.
      */
     ble_error_t allowLegacyPairing(bool allow = true);
 
     /**
      * Check if the Secure Connections feature is supported by the stack and controller.
      *
      * @param[out] enabled true if SC are supported
      * @return BLE_ERROR_NONE or appropriate error code indicating the failure reason.
      */
     ble_error_t getSecureConnectionsSupport(bool *enabled);
 #endif // BLE_FEATURE_SECURE_CONNECTIONS
 
     ////////////////////////////////////////////////////////////////////////////
     // Security settings
     //
 
     /**
      * Set the IO capability of the local device.
      *
      * @param[in] iocaps type of IO capabilities available on the local device
      * @return BLE_ERROR_NONE or appropriate error code indicating the failure reason.
      */
     ble_error_t setIoCapability(SecurityIOCapabilities_t iocaps);
 
     /**
      * Set the passkey that is displayed on the local device instead of using
      * a randomly generated one
      *
      * @param[in] passkey ASCII string of 6 digits
      * @return BLE_ERROR_NONE or appropriate error code indicating the failure reason.
      */
     ble_error_t setDisplayPasskey(const Passkey_t passkey);
 
     /**
      * Set the security mode on a connection. Useful for elevating the security mode
      * once certain conditions are met, e.g., a particular service is found.
      *
      * @param[in]  connectionHandle   Handle to identify the connection.
      * @param[in]  securityMode       Requested security mode.
      *
      * @return BLE_ERROR_NONE or appropriate error code indicating the failure reason.
      */
     ble_error_t setLinkSecurity(ble::connection_handle_t connectionHandle, SecurityMode_t securityMode);
 
     /**
      * Set whether or not we want to send and receive keypress notifications
      * during passkey entry.
      *
      * @param[in] enabled if true pairing will try to enable keypress notifications
      * (dependent on other side supporting it)
      *
      * @return BLE_ERROR_NONE or appropriate error code indicating the failure reason.
      */
     ble_error_t setKeypressNotification(bool enabled = true);
 
 #if BLE_FEATURE_SIGNING
     /**
      * Request generation and exchange of signing keys so that packet signing can be utilised
      * on this connection.
      * @note This does not generate a signingKey event. Use getSigningKey for that.
      *
      * @param[in] connectionHandle Handle to identify the connection.
      * @param[in] enabled          If set to true, signing keys will be exchanged
      *                             during subsequent pairing.
      * @return BLE_ERROR_NONE or appropriate error code indicating the failure reason.
      */
     ble_error_t enableSigning(ble::connection_handle_t connectionHandle, bool enabled = true);
 #endif // BLE_FEATURE_SIGNING
 
     /**
      * Give a hint to the stack that the master/slave role might change in the future.
      *
      * @param[in] enable If set to true it hints the roles are likely to swap in the future.
      *
      * @return BLE_ERROR_NONE or appropriate error code indicating the failure reason.
      */
     ble_error_t setHintFutureRoleReversal(bool enable = true);
 
     ////////////////////////////////////////////////////////////////////////////
     // Encryption
     //
 
     /**
      * Current state of encryption on the link.
      *
      * @param[in] connectionHandle Handle to identify the connection.
      * @param[out] encryption
      * @return BLE_ERROR_NONE or appropriate error code indicating the failure reason.
      */
     ble_error_t getLinkEncryption(ble::connection_handle_t connectionHandle, ble::link_encryption_t *encryption);
 
     /**
      * Enabled or disable encryption on the link. The result of this request will be indicated
      * by a call to linkEncryptionResult in the event handler when the action is completed.
      *
      * @param[in] connectionHandle Handle to identify the connection.
      * @param[in] encryption encryption state requested
      * @return BLE_ERROR_NONE or appropriate error code indicating the failure reason.
      */
     ble_error_t setLinkEncryption(ble::connection_handle_t connectionHandle, ble::link_encryption_t encryption);
 
     /**
      * Set the requirements for encryption key size. If the peer cannot comply with the requirements
      * paring will fail.
      *
      * @param[in] minimumByteSize Smallest allowed encryption key size in bytes. (no smaller than 7)
      * @param[in] maximumByteSize Largest allowed encryption key size in bytes. (no larger than 16)
      * @return BLE_ERROR_NONE or appropriate error code indicating the failure reason.
      */
     ble_error_t setEncryptionKeyRequirements(uint8_t minimumByteSize, uint8_t maximumByteSize);
 
     /**
      * Get encryption key size for given connection.
      *
      * @param[in] connectionHandle Handle to identify the connection.
      * @param[out] size Returns the key size in bits.
      *
      * @return BLE_ERROR_NONE or appropriate error code indicating the failure reason.
      */
     ble_error_t getEncryptionKeySize(
         connection_handle_t connectionHandle,
         uint8_t *size
     );
 
     ////////////////////////////////////////////////////////////////////////////
     // Authentication
     //
 
     /**
      * Request that the link be authenticated (keys with MITM protection). This might trigger encryption
      * or pairing/re-pairing. The success will be indicated through an event indicating security level change.
      *
      * @param[in] connectionHandle Handle to identify the connection.
      * @return BLE_ERROR_NONE or appropriate error code indicating the failure reason.
      */
     ble_error_t requestAuthentication(ble::connection_handle_t connectionHandle);
 
     ////////////////////////////////////////////////////////////////////////////
     // MITM
     //
 
     /**
      * Generate OOB data with the given address. If Secure Connections is supported this will
      * also generate Secure Connections OOB data on top of legacy pairing OOB data. This can be used
      * to generate such data before the connection takes place.
      *
      * In this model the OOB exchange takes place before the devices connect. Devices should establish
      * communication over another channel and exchange the OOB data. The address provided will be used
      * by the peer to associate the received data with the address of the device it will then connect
      * to over BLE.
      *
      * @param[in] address The local address you will use in the connection using this OOB data. This
      *                    address will be returned along with the rest of the OOB data when generation
      *                    is complete. Using an invalid address is illegal.
      * @return BLE_ERROR_NONE or appropriate error code indicating the failure reason.
      */
     ble_error_t generateOOB(const ble::address_t *address);
 
     /**
      * Enable OOB data usage during paring. If Secure Connections is supported enabling useOOB will
      * generate Secure Connections OOB data through oobGenerated() on top of legacy pairing OOB data.
      *
      * You do not have to call this function to return received OOB data. Use legacyPairingOobReceived
      * or oobReceived to hand it in. This will allow the stack to use it if possible. You only need to
      * call this function to attempt legacy OOB data exchange after pairing start and to inform
      * the stack OOB data does not provide MITM protection (by default it is set to provide this).
      *
      * In this model the OOB exchange takes places after the devices have connected but possibly
      * prior to pairing. For secure connections pairing must not be started until after the OOB
      * data has been sent and/or received. The address in the OOB data generated will match
      * the original address used to establish the connection and will be used by the peer to
      * identify which connection the OOB data belongs to.
      *
      * @param[in] connectionHandle Handle to identify the connection.
      * @param[in] useOOB If set to true, authenticate using OOB data.
      * @param[in] OOBProvidesMITM If set to true keys exchanged during pairing using OOB data
      *                            will provide Man-in-the-Middle protection. This indicates that
      *                            the form of exchange used by the OOB data itself provides MITM
      *                            protection.
      * @return BLE_ERROR_NONE or appropriate error code indicating the failure reason.
      */
     ble_error_t setOOBDataUsage(ble::connection_handle_t connectionHandle, bool useOOB, bool OOBProvidesMITM = true);
 
 #if BLE_FEATURE_SECURE_CONNECTIONS
     /**
      * Report to the stack if the passkey matches or not. Used during pairing to provide MITM protection.
      *
      * @param[in] connectionHandle Handle to identify the connection.
      * @param[in] confirmation True value indicates the passkey displayed matches.
      * @return BLE_ERROR_NONE or appropriate error code indicating the failure reason.
      */
     ble_error_t confirmationEntered(ble::connection_handle_t connectionHandle, bool confirmation);
 #endif // BLE_FEATURE_SECURE_CONNECTIONS
 
     /**
      * Supply the stack with the user entered passkey.
      *
      * @param[in] connectionHandle Handle to identify the connection.
      * @param[in] passkey ASCII string of digits entered by the user.
      * @return BLE_ERROR_NONE or appropriate error code indicating the failure reason.
      */
     ble_error_t passkeyEntered(ble::connection_handle_t connectionHandle, Passkey_t passkey);
 
 #if BLE_FEATURE_SECURE_CONNECTIONS
     /**
      * Send a notification to the peer that the user pressed a key on the local device.
      * @note This will only be delivered if the keypress notifications have been enabled during pairing.
      *
      * @param[in] connectionHandle Handle to identify the connection.
      * @param[in] keypress Type of keypress event.
      * @return BLE_ERROR_NONE or appropriate error code indicating the failure reason.
      */
     ble_error_t sendKeypressNotification(ble::connection_handle_t connectionHandle, ble::Keypress_t keypress);
 #endif // BLE_FEATURE_SECURE_CONNECTIONS
 
     /**
      * Supply the stack with the OOB data for legacy connections.
      *
      * @param[in] address address of the peer device this data comes from
      * @param[in] tk pointer to out of band data received containing the temporary key.
      * @return BLE_ERROR_NONE or appropriate error code indicating the failure reason.
      */
     ble_error_t legacyPairingOobReceived(const ble::address_t *address, const ble::oob_tk_t *tk);
 
 #if BLE_FEATURE_SECURE_CONNECTIONS
     /**
      * Supply the stack with the OOB data for secure connections.
      *
      * @param[in] address address of the peer device this data comes from
      * @param[in] random random number used to generate the confirmation
      * @param[in] confirm confirmation value to be use for authentication
      *                    in secure connections pairing
      * @return BLE_ERROR_NONE or appropriate error code indicating the failure reason.
      */
     ble_error_t oobReceived(const ble::address_t *address, const ble::oob_lesc_value_t *random, const ble::oob_confirm_t *confirm);
 #endif // BLE_FEATURE_SECURE_CONNECTIONS
 
     ////////////////////////////////////////////////////////////////////////////
     // Keys
     //
 
 #if BLE_FEATURE_SIGNING
     /**
      * Retrieves a signing key through a signingKey event.
      * If a signing key is not present, pairing/authentication will be attempted.
      * @note This will attempt to retrieve the key even if enableSigning hasn't been called prior to pairing.
      *
      * @param[in] connectionHandle Handle to identify the connection.
      * @param[in] authenticated    Whether the signing key needs to be authenticated
      *                             (provide MITM protection).
      *
      * @return BLE_ERROR_NONE or appropriate error code indicating the failure reason.
      */
     ble_error_t getSigningKey(ble::connection_handle_t connectionHandle, bool authenticated);
 #endif // BLE_FEATURE_SIGNING
 
     ////////////////////////////////////////////////////////////////////////////
     // Privacy
     //
 
 #if BLE_FEATURE_PRIVACY
     /**
      * Sets how often the address is rotated when privacy is enabled.
      *
      * @param[in] timeout_in_seconds How many seconds to wait before starting generation of a new address.
      *
      * @return BLE_ERROR_NONE or appropriate error code indicating the failure reason.
      */
     ble_error_t setPrivateAddressTimeout(
         uint16_t timeout_in_seconds
     );
 #endif // BLE_FEATURE_PRIVACY
 
     /* Event callback handlers. */
 public:
     /**
      * Setup a callback to be invoked to notify the user application that the
      * SecurityManager instance is about to shutdown (possibly as a result of a call
      * to BLE::shutdown()).
      *
      * @note  It is possible to chain together multiple onShutdown callbacks
      * (potentially from different modules of an application) to be notified
      * before the SecurityManager is shutdown.
      *
      * @note  It is also possible to set up a callback into a member function of
      * some object.
      *
      * @note It is possible to unregister a callback using onShutdown().detach(callback)
      */
     void onShutdown(const SecurityManagerShutdownCallback_t& callback);
 
     template <typename T>
     void onShutdown(T *objPtr, void (T::*memberPtr)(const SecurityManager *))
     {
         onShutdown({objPtr, memberPtr});
     }
 
     /**
      * Provide access to the callchain of shutdown event callbacks.
      * It is possible to register callbacks using onShutdown().add(callback).
      * It is possible to unregister callbacks using onShutdown().detach(callback).
      *
      * @return The shutdown event callbacks chain
      */
     SecurityManagerShutdownCallbackChain_t& onShutdown();
 
     /**
      * Assign the event handler implementation that will be used by the stack to signal events
      * back to the application.
      *
      * @param[in] handler Event Handler interface implementation.
      */
     void setSecurityManagerEventHandler(EventHandler* handler);
 
 public:
 #if !defined(DOXYGEN_ONLY)
     /** For backwards compatibility. This enum is now in BLETypes.h
      * @deprecated use the enum in ble namespace */
     typedef ble::Keypress_t Keypress_t;
 
     SecurityManager(impl::SecurityManager* impl) : impl(impl) {}
     SecurityManager(const SecurityManager&) = delete;
     SecurityManager& operator=(const SecurityManager&) = delete;
 #endif // !defined(DOXYGEN_ONLY)
 
 private:
     impl::SecurityManager *impl;
 };
 
 } // ble
 
 /** @deprecated Use the namespaced ble::SecurityManager instead of the global SecurityManager. */
 using ble::SecurityManager;
 
 #endif /*BLE_SECURITY_MANAGER_H_*/
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