CRYPTO(9)                 BSD Kernel Developer's Manual                CRYPTO(9)

     crypto — API for cryptographic services in the kernel

     #include <opencrypto/cryptodev.h>

     crypto_get_driverid(device_t, size_t, int);

     crypto_register(uint32_t, int, uint16_t, uint32_t,
         int (*)(void *, uint32_t *, struct cryptoini *),
         int (*)(void *, uint64_t), int (*)(void *, struct cryptop *), void *);

     crypto_kregister(uint32_t, int, uint32_t,
         int (*)(void *, struct cryptkop *), void *);

     crypto_unregister(uint32_t, int);


     crypto_done(struct cryptop *);

     crypto_kdone(struct cryptkop *);

     crypto_find_driver(const char *);

     crypto_newsession(crypto_session_t *, struct cryptoini *, int);


     crypto_dispatch(struct cryptop *);

     crypto_kdispatch(struct cryptkop *);

     crypto_unblock(uint32_t, int);

     struct cryptop *


     #define CRYPTO_SYMQ     0x1
     #define CRYPTO_ASYMQ    0x2

     #define EALG_MAX_BLOCK_LEN      16

     struct cryptoini {
             int                cri_alg;
             int                cri_klen;
             int                cri_mlen;
             caddr_t            cri_key;
             uint8_t            cri_iv[EALG_MAX_BLOCK_LEN];
             struct cryptoini  *cri_next;

     struct cryptodesc {
             int                crd_skip;
             int                crd_len;
             int                crd_inject;
             int                crd_flags;
             struct cryptoini   CRD_INI;
     #define crd_iv          CRD_INI.cri_iv
     #define crd_key         CRD_INI.cri_key
     #define crd_alg         CRD_INI.cri_alg
     #define crd_klen        CRD_INI.cri_klen
             struct cryptodesc *crd_next;

     struct cryptop {
             TAILQ_ENTRY(cryptop) crp_next;
             crypto_session_t   crp_session;
             int                crp_ilen;
             int                crp_olen;
             int                crp_etype;
             int                crp_flags;
             caddr_t            crp_buf;
             caddr_t            crp_opaque;
             struct cryptodesc *crp_desc;
             int              (*crp_callback) (struct cryptop *);
             caddr_t            crp_mac;

     struct crparam {
             caddr_t         crp_p;
             u_int           crp_nbits;

     #define CRK_MAXPARAM    8

     struct cryptkop {
             TAILQ_ENTRY(cryptkop) krp_next;
             u_int              krp_op;         /* ie. CRK_MOD_EXP or other */
             u_int              krp_status;     /* return status */
             u_short            krp_iparams;    /* # of input parameters */
             u_short            krp_oparams;    /* # of output parameters */
             uint32_t           krp_hid;
             struct crparam     krp_param[CRK_MAXPARAM];
             int               (*krp_callback)(struct cryptkop *);

     crypto is a framework for drivers of cryptographic hardware to register
     with the kernel so “consumers” (other kernel subsystems, and users through
     the /dev/crypto device) are able to make use of it.  Drivers register with
     the framework the algorithms they support, and provide entry points
     (functions) the framework may call to establish, use, and tear down
     sessions.  Sessions are used to cache cryptographic information in a
     particular driver (or associated hardware), so initialization is not needed
     with every request.  Consumers of cryptographic services pass a set of
     descriptors that instruct the framework (and the drivers registered with
     it) of the operations that should be applied on the data (more than one
     cryptographic operation can be requested).

     Keying operations are supported as well.  Unlike the symmetric operators
     described above, these sessionless commands perform mathematical operations
     using input and output parameters.

     Since the consumers may not be associated with a process, drivers may not
     sleep(9).  The same holds for the framework.  Thus, a callback mechanism is
     used to notify a consumer that a request has been completed (the callback
     is specified by the consumer on a per-request basis).  The callback is
     invoked by the framework whether the request was successfully completed or
     not.  An error indication is provided in the latter case.  A specific error
     code, EAGAIN, is used to indicate that a session handle has changed and
     that the request may be re-submitted immediately with the new session.
     Errors are only returned to the invoking function if not enough information
     to call the callback is available (meaning, there was a fatal error in
     verifying the arguments).  For session initialization and teardown no
     callback mechanism is used.

     The crypto_find_driver() function may be called to return the specific id
     of the provided name.  If the specified driver could not be found, the
     returned id is -1.

     The crypto_newsession() routine is called by consumers of cryptographic
     services (such as the ipsec(4) stack) that wish to establish a new session
     with the framework.  The second argument contains all the necessary
     information for the driver to establish the session.  The third argument is
     either a specific driver id, or one or both of CRYPTOCAP_F_HARDWARE, to
     select hardware devices, or CRYPTOCAP_F_SOFTWARE, to select software
     devices.  If both are specified, a hardware device will be returned before
     a software device will be.  On success, the value pointed to by the first
     argument will be the opaque session handle.  The various fields in the
     cryptoini structure are:

     cri_alg   Contains an algorithm identifier.  Currently supported algorithms


     cri_klen  Specifies the length of the key in bits, for variable-size key

     cri_mlen  Specifies how many bytes from the calculated hash should be
               copied back.  0 means entire hash.

     cri_key   Contains the key to be used with the algorithm.

     cri_iv    Contains an explicit initialization vector (IV), if it does not
               prefix the data.  This field is ignored during initialization
               (crypto_newsession).  If no IV is explicitly passed (see below on
               details), a random IV is used by the device driver processing the

     cri_next  Contains a pointer to another cryptoini structure.  Multiple such
               structures may be linked to establish multi-algorithm sessions
               (ipsec(4) is an example consumer of such a feature).

     The cryptoini structure and its contents will not be modified by the
     framework (or the drivers used).

     crypto_freesession() is called with the session handle returned by
     crypto_newsession() to free the session.

     crypto_dispatch() is called to process a request.  The various fields in
     the cryptop structure are:

     crp_session   Contains the session handle.

     crp_ilen      Indicates the total length in bytes of the buffer to be

     crp_olen      On return, contains the total length of the result.  For
                   symmetric crypto operations, this will be the same as the
                   input length.  This will be used if the framework needs to
                   allocate a new buffer for the result (or for re-formatting
                   the input).

     crp_callback  This routine is invoked upon completion of the request,
                   whether successful or not.  It is invoked through the
                   crypto_done() routine.  If the request was not successful, an
                   error code is set in the crp_etype field.  It is the
                   responsibility of the callback routine to set the appropriate
                   spl(9) level.

     crp_etype     Contains the error type, if any errors were encountered, or
                   zero if the request was successfully processed.  If the
                   EAGAIN error code is returned, the session handle has changed
                   (and has been recorded in the crp_session field).  The
                   consumer should record the new session handle and use it in
                   all subsequent requests.  In this case, the request may be
                   re-submitted immediately.  This mechanism is used by the
                   framework to perform session migration (move a session from
                   one driver to another, because of availability, performance,
                   or other considerations).

                   Note that this field only makes sense when examined by the
                   callback routine specified in crp_callback.  Errors are
                   returned to the invoker of crypto_process() only when enough
                   information is not present to call the callback routine
                   (i.e., if the pointer passed is NULL or if no callback
                   routine was specified).

     crp_flags     Is a bitmask of flags associated with this request.
                   Currently defined flags are:

                   CRYPTO_F_IMBUF     The buffer pointed to by crp_buf is an
                                      mbuf chain.

                   CRYPTO_F_IOV       The buffer pointed to by crp_buf is an uio

                   CRYPTO_F_BATCH     Batch operation if possible.

                   CRYPTO_F_CBIMM     Do callback immediately instead of doing
                                      it from a dedicated kernel thread.

                   CRYPTO_F_DONE      Operation completed.

                   CRYPTO_F_CBIFSYNC  Do callback immediately if operation is
                                      synchronous (that the driver specified the
                                      CRYPTOCAP_F_SYNC flag).

                   CRYPTO_F_ASYNC     Try to do the crypto operation in a pool
                                      of workers if the operation is synchronous
                                      (that is, if the driver specified the
                                      CRYPTOCAP_F_SYNC flag).  It aims to speed
                                      up processing by dispatching crypto
                                      operations on different processors.

                                      Dispatch callbacks in the same order they
                                      are posted.  Only relevant if the
                                      CRYPTO_F_ASYNC flag is set and if the
                                      operation is synchronous.

     crp_buf       Points to the input buffer.  On return (when the callback is
                   invoked), it contains the result of the request.  The input
                   buffer may be an mbuf chain or a contiguous buffer, depending
                   on crp_flags.

     crp_opaque    This is passed through the crypto framework untouched and is
                   intended for the invoking application's use.

     crp_desc      This is a linked list of descriptors.  Each descriptor
                   provides information about what type of cryptographic
                   operation should be done on the input buffer.  The various
                   fields are:

                   crd_iv      When the flag CRD_F_IV_EXPLICIT is set, this
                               field contains the IV.

                   crd_key     When the CRD_F_KEY_EXPLICIT flag is set, the
                               crd_key points to a buffer with encryption or
                               authentication key.

                   crd_alg     An algorithm to use.  Must be the same as the one
                               given at newsession time.

                   crd_klen    The crd_key key length.

                   crd_skip    The offset in the input buffer where processing
                               should start.

                   crd_len     How many bytes, after crd_skip, should be

                   crd_inject  The crd_inject field specifies an offset in bytes
                               from the beginning of the buffer.  For encryption
                               algorithms, this may be where the IV will be
                               inserted when encrypting or where the IV may be
                               found for decryption (subject to crd_flags).  For
                               MAC algorithms, this is where the result of the
                               keyed hash will be inserted.

                   crd_flags   The following flags are defined:

                                    For encryption algorithms, this bit is set
                                    when encryption is required (when not set,
                                    decryption is performed).

                                    For encryption, if this bit is not set the
                                    IV used to encrypt the packet will be
                                    written at the location pointed to by
                                    crd_inject.  The IV length is assumed to be
                                    equal to the blocksize of the encryption
                                    algorithm.  For encryption, if this bit is
                                    set, nothing is done.  For decryption, this
                                    flag has no meaning.  Applications that do
                                    special “IV cooking”, such as the half-IV
                                    mode in ipsec(4), can use this flag to
                                    indicate that the IV should not be written
                                    on the packet.  This flag is typically used
                                    in conjunction with the CRD_F_IV_EXPLICIT

                                    This bit is set when the IV is explicitly
                                    provided by the consumer in the crd_iv
                                    field.  Otherwise, for encryption operations
                                    the IV is provided for by the driver used to
                                    perform the operation, whereas for
                                    decryption operations the offset of the IV
                                    is provided by the crd_inject field.  This
                                    flag is typically used when the IV is
                                    calculated “on the fly” by the consumer, and
                                    does not precede the data (some ipsec(4)
                                    configurations, and the encrypted swap are
                                    two such examples).

                                    For encryption and authentication (MAC)
                                    algorithms, this bit is set when the key is
                                    explicitly provided by the consumer in the
                                    crd_key field for the given operation.
                                    Otherwise, the key is taken at newsession
                                    time from the cri_key field.  As calculating
                                    the key schedule may take a while, it is
                                    recommended that often used keys are given
                                    their own session.

                                    For compression algorithms, this bit is set
                                    when compression is required (when not set,
                                    decompression is performed).

                   CRD_INI     This cryptoini structure will not be modified by
                               the framework or the device drivers.  Since this
                               information accompanies every cryptographic
                               operation request, drivers may re-initialize
                               state on-demand (typically an expensive
                               operation).  Furthermore, the cryptographic
                               framework may re-route requests as a result of
                               full queues or hardware failure, as described

                   crd_next    Point to the next descriptor.  Linked operations
                               are useful in protocols such as ipsec(4), where
                               multiple cryptographic transforms may be applied
                               on the same block of data.

     crypto_getreq() allocates a cryptop structure with a linked list of as many
     cryptodesc structures as were specified in the argument passed to it.

     crypto_freereq() deallocates a structure cryptop and any cryptodesc
     structures linked to it.  Note that it is the responsibility of the
     callback routine to do the necessary cleanups associated with the opaque
     field in the cryptop structure.

     crypto_kdispatch() is called to perform a keying operation.  The various
     fields in the cryptkop structure are:

     krp_op        Operation code, such as CRK_MOD_EXP.

     krp_status    Return code.  This errno-style variable indicates whether
                   lower level reasons for operation failure.

     krp_iparams   Number if input parameters to the specified operation.  Note
                   that each operation has a (typically hardwired) number of
                   such parameters.

     krp_oparams   Number if output parameters from the specified operation.
                   Note that each operation has a (typically hardwired) number
                   of such parameters.

     krp_kvp       An array of kernel memory blocks containing the parameters.

     krp_hid       Identifier specifying which low-level driver is being used.

     krp_callback  Callback called on completion of a keying operation.

     The crypto_get_driverid(), crypto_get_driver_session(), crypto_register(),
     crypto_kregister(), crypto_unregister(), crypto_unblock(), and
     crypto_done() routines are used by drivers that provide support for
     cryptographic primitives to register and unregister with the kernel crypto
     services framework.

     Drivers must first use the crypto_get_driverid() function to acquire a
     driver identifier, specifying the flags as an argument.  One of
     CRYPTOCAP_F_SYNC may also be specified, and should be specified if the
     driver does all of it's operations synchronously.  Drivers must pass the
     size of their session struct as the second argument.  An appropriately
     sized memory will be allocated by the framework, zeroed, and passed to the
     driver's newsession() method.

     For each algorithm the driver supports, it must then call
     crypto_register().  The first two arguments are the driver and algorithm
     identifiers.  The next two arguments specify the largest possible operator
     length (in bits, important for public key operations) and flags for this
     algorithm.  The last four arguments must be provided in the first call to
     crypto_register() and are ignored in all subsequent calls.  They are
     pointers to three driver-provided functions that the framework may call to
     establish new cryptographic context with the driver, free already
     established context, and ask for a request to be processed (encrypt,
     decrypt, etc.); and an opaque parameter to pass when calling each of these

     crypto_unregister() is called by drivers that wish to withdraw support for
     an algorithm.  The two arguments are the driver and algorithm identifiers,
     respectively.  Typically, drivers for PCMCIA crypto cards that are being
     ejected will invoke this routine for all algorithms supported by the card.
     crypto_unregister_all() will unregister all algorithms registered by a
     driver and the driver will be disabled (no new sessions will be allocated
     on that driver, and any existing sessions will be migrated to other
     drivers).  The same will be done if all algorithms associated with a driver
     are unregistered one by one.  After a call to crypto_unregister_all() there
     will be no threads in either the newsession or freesession function of the

     The calling convention for the driver-supplied routines are:

     int (*newsession)(device_t, crypto_session_t, struct cryptoini *);
     void (*freesession)(device_t, crypto_session_t);
     int (*process)(device_t, struct cryptop *, int);
     int (*kprocess)(device_t, struct cryptkop *, int);

     On invocation, the first argument to all routines is the device_t that was
     provided to crypto_get_driverid().  The second argument to newsession() is
     the opaque session handle for the new session.  The third argument is
     identical to that of crypto_newsession().

     Drivers obtain a pointer to their session memory by invoking
     crypto_get_driver_session() on the opaque crypto_session_t handle.

     The freesession() routine takes as arguments the opaque data value and the
     session handle.  It should clear any context associated with the session
     (clear hardware registers, memory, etc.).  If no resources need to be
     released other than the contents of session memory, the method is optional.
     The crypto framework will zero and release the allocated session memory
     (after running the freesession() method, if one exists).

     The process() routine is invoked with a request to perform crypto
     processing.  This routine must not block or sleep, but should queue the
     request and return immediately or process the request to completion.  In
     case of an unrecoverable error, the error indication must be placed in the
     crp_etype field of the cryptop structure.  When the request is completed,
     or an error is detected, the process() routine must invoke crypto_done().
     Session migration may be performed, as mentioned previously.

     In case of a temporary resource exhaustion, the process() routine may
     return ERESTART in which case the crypto services will requeue the request,
     mark the driver as “blocked”, and stop submitting requests for processing.
     The driver is then responsible for notifying the crypto services when it is
     again able to process requests through the crypto_unblock() routine.  This
     simple flow control mechanism should only be used for short-lived resource
     exhaustion as it causes operations to be queued in the crypto layer.  Doing
     so is preferable to returning an error in such cases as it can cause
     network protocols to degrade performance by treating the failure much like
     a lost packet.

     The kprocess() routine is invoked with a request to perform crypto key
     processing.  This routine must not block, but should queue the request and
     return immediately.  Upon processing the request, the callback routine
     should be invoked.  In case of an unrecoverable error, the error indication
     must be placed in the krp_status field of the cryptkop structure.  When the
     request is completed, or an error is detected, the kprocess() routine
     should invoked crypto_kdone().

     crypto_register(), crypto_kregister(), crypto_unregister(),
     crypto_newsession(), crypto_freesession(), and crypto_unblock() return 0 on
     success, or an error code on failure.  crypto_get_driverid() returns a non-
     negative value on error, and -1 on failure.  crypto_getreq() returns a
     pointer to a cryptop structure and NULL on failure.  crypto_dispatch()
     returns EINVAL if its argument or the callback function was NULL, and 0
     otherwise.  The callback is provided with an error code in case of failure,
     in the crp_etype field.

     sys/opencrypto/crypto.c  most of the framework code

     crypto(4), ipsec(4), crypto(7), malloc(9), sleep(9)

     The cryptographic framework first appeared in OpenBSD 2.7 and was written
     by Angelos D. Keromytis <>.

     The framework currently assumes that all the algorithms in a
     crypto_newsession() operation must be available by the same driver.  If
     that is not the case, session initialization will fail.

     The framework also needs a mechanism for determining which driver is best
     for a specific set of algorithms associated with a session.  Some type of
     benchmarking is in order here.

     Multiple instances of the same algorithm in the same session are not

BSD                               July 17, 2018                              BSD