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     crypto — API for cryptographic services in the kernel


     #include <opencrypto/cryptodev.h>


     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_newsession(uint64_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;
             uint64_t           crp_sid;
             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

     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 number has changed and that the request may
     be re-submitted immediately with the new session number.  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 there is no callback mechanism used.

     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.  On success,
     the first argument will contain the Session Identifier (SID).  The second argument contains
     all the necessary information for the driver to establish the session.  The third argument
     indicates whether a hardware driver (1) should be used or not (0).  The various fields in
     the cryptoini structure are:

     cri_alg   Contains an algorithm identifier.  Currently supported algorithms are:


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

     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.  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).  Subsequent requests for processing that use the SID returned will avoid the
     cost of re-initializing the hardware (in essence, SID acts as an index in the session cache
     of the driver).

     crypto_freesession() is called with the SID returned by crypto_newsession() to disestablish
     the session.

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

     crp_sid       Contains the SID.

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

     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
                   SID has changed (and has been recorded in the crp_sid field).  The consumer
                   should record the new SID 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

                   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 structure.

                   CRYPTO_F_REL       Must return data in the same place.

                   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.

     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      The field where IV should be provided when the CRD_F_IV_EXPLICIT
                               flag is given.

                   crd_key     When the CRD_F_KEY_EXPLICIT flag is given, 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 processed.

                   crd_inject  Offset from the beginning of the buffer to insert any results.
                               For encryption algorithms, this is where the initialization vector
                               (IV) will be inserted when encrypting or where it can be found
                               when decrypting (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 algorithms, this bit is set when the IV
                                    already precedes the data, so the crd_inject value will be
                                    ignored and no IV will be written in the buffer.  Otherwise,
                                    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.
                                    Some 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

                                    For encryption algorithms, 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 it is pointed to 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.

                                    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 above.

                   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_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 cc_flags as an argument (normally 0, but software-only drivers
     should specify CRYPTOCAP_F_SOFTWARE).  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 routines.  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.

     The calling convention for the three driver-supplied routines is:

     int (*newsession)(void *, uint32_t *, struct cryptoini *);
     int (*freesession)(void *, uint64_t);
     int (*process)(void *, struct cryptop *);
     int (*kprocess)(void *, struct cryptkop *);

     On invocation, the first argument to all routines is an opaque data value supplied when the
     algorithm is registered with crypto_register().  The second argument to newsession()
     contains the driver identifier obtained via crypto_get_driverid().  On successful return, it
     should contain a driver-specific session identifier.  The third argument is identical to
     that of crypto_newsession().

     The freesession() routine takes as arguments the opaque data value and the SID (which is the
     concatenation of the driver identifier and the driver-specific session identifier).  It
     should clear any context associated with the session (clear hardware registers, memory,

     The process() routine is invoked with a request to perform crypto 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 crp_etype field of the cryptop structure.  When the
     request is completed, or an error is detected, the process() routine should 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


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


     ipsec(4), 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

     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 supported.  Note that
     3DES is considered one algorithm (and not three instances of DES).  Thus, 3DES and DES could
     be mixed in the same request.