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

     crypto -- API for cryptographic services in the kernel

     #include <opencrypto/cryptodev.h>


     crypto_register(u_int32_t, int, u_int16_t, u_int32_t,
         int (*)(void *, u_int32_t *, struct cryptoini *),
         int (*)(void *, u_int64_t), int (*)(void *, struct cryptop *),
         void *);

     crypto_kregister(u_int32_t, int, u_int32_t,
         int (*)(void *, struct cryptkop *), void *);

     crypto_unregister(u_int32_t, int);


     crypto_done(struct cryptop *);

     crypto_kdone(struct cryptkop *);

     crypto_newsession(u_int64_t *, struct cryptoini *, int);


     crypto_dispatch(struct cryptop *);

     crypto_kdispatch(struct cryptkop *);

     crypto_unblock(u_int32_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_rnd;
             caddr_t            cri_key;
             u_int8_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;
             struct cryptodesc *crd_next;

     struct cryptop {
             TAILQ_ENTRY(cryptop) crp_next;
             u_int64_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 */
             u_int32_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 reg-
     ister 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 regis-
     tered 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 opera-
     tions 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 call-
     back is specified by the consumer on an per-request basis).  The callback
     is invoked by the framework whether the request was successfully com-
     pleted 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 initializa-
     tion 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 ses-
     sion 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 algo-
               rithms are:


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

     cri_rnd   Specifies the number of rounds to be used with the algorithm,
               for variable-round algorithms.

     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 request.

     cri_next  Contains a pointer to another cryptoini structure.  Multiple
               such structures may be linked to establish multi-algorithm ses-
               sions (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

     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 appropri-
                   ate 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 considera-

                   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 rou-
                   tine (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.  Cur-
                   rently defined flags are:

                   CRYPTO_F_IMBUF  The buffer pointed to by crp_buf is an mbuf

     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 pro-
                   vides information about what type of cryptographic opera-
                   tion should be done on the input buffer.  The various
                   fields are:

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

                   crd_len     How many bytes, after crd_skip, should be pro-

                   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:

                               CRD_F_ENCRYPT      For encryption algorithms,
                                                  this bit is set when encryp-
                                                  tion is required (when not
                                                  set, decryption is per-

                               CRD_F_IV_PRESENT   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.  Oth-
                                                  erwise, 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 typi-
                                                  cally used in conjunction
                                                  with the CRD_F_IV_EXPLICIT

                               CRD_F_IV_EXPLICIT  For encryption algorithms,
                                                  this bit is set when the IV
                                                  is explicitly provided by
                                                  the consumer in the cri_iv
                                                  fields.  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 typi-
                                                  cally 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).

                               CRD_F_COMP         For compression algorithms,
                                                  this bit is set when com-
                                                  pression is required (when
                                                  not set, decompression is

                   CRD_INI     This cryptoini structure will not be modified
                               by the framework or the device drivers.  Since
                               this information accompanies every crypto-
                               graphic operation request, drivers may re-ini-
                               tialize 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 opera-
                               tions 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

     crypto_freereq() deallocates a structure cryptop and any cryptodesc
     structures linked to it.  Note that it is the responsibility of the call-
     back 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) num-
                    ber of such parameters.

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

     krp_kvp        An array of kernel memory blocks containing the parame-

     krp_hid        Identifier specifying which low-level driver is being

     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 reg-
     ister 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 soft-
     ware-only drivers should specify CRYPTOCAP_F_SOFTWARE).  For each algo-
     rithm 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 unregis-
     ter all algorithms registered by a driver and the driver will be disabled
     (no new sessions will be allocated on that driver, and any existing ses-
     sions 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 *, u_int32_t *, struct cryptoini *);
     int (*freesession)(void *, u_int64_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 associ-
     ated with the session (clear hardware registers, memory, etc.).

     The process() routine is invoked with a request to perform crypto pro-
     cessing.  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 indica-
     tion 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 ser-
     vices 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 rou-
     tine should be invoked.  In case of an unrecoverable error, the error
     indication must be placed in the krp_status field of the cryptkop struc-
     ture.  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 fail-
     ure, in the crp_etype field.

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

FreeBSD 6.2                    October 14, 2002                    FreeBSD 6.2


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