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

NAME
     crypto -- API for cryptographic services in the kernel

SYNOPSIS
     #include <&lt;crypto/cryptodev.h>&gt;

     int32_t
     crypto_get_driverid(u_int8_t);

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

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

     int
     crypto_unregister(u_int32_t, int);

     void
     crypto_done(struct cryptop *);

     void
     crypto_kdone(struct cryptkop *);

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

     int
     crypto_freesession(u_int64_t);

     int
     crypto_dispatch(struct cryptop *);

     int
     crypto_kdispatch(struct cryptkop *);

     struct cryptop *
     crypto_getreq(int);

     void
     crypto_freereq(struct cryptop *);


     #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 {
             u_int64_t          crp_sid;
             int                crp_ilen;
             int                crp_olen;
             int                crp_alloctype;
             int                crp_etype;
             int                crp_flags;
             void              *crp_buf;
             void              *crp_opaque;
             struct cryptodesc *crp_desc;
             int              (*crp_callback)(struct cryptop *);
             struct cryptop    *crp_next;
             caddr_t            crp_mac;
     };

     struct crparam {
             caddr_t         crp_p;
             u_int           crp_nbits;
     };

     #define CRK_MAXPARAM    8

     struct cryptkop {
             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];       /* kvm */
             int               (*krp_callback)(struct cryptkop *);
             struct cryptkop   *krp_next;
     };

DESCRIPTION
     crypto is a framework for drivers of cryptographic hardware to register
     with the kernel so ``consumers'' (other kernel subsystems, and eventually
     users through an appropriate 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 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
     use tsleep(9).  The same holds for the framework.  Thus, a callback mech-
     anism 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 call-
     back 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 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 should be used (1) or not (0).  The
     various fields in the cryptoini structure are:

     cri_alg       Contains an algorithm identifier.  Currently supported
                   algorithms are:

                   CRYPTO_DES_CBC
                   CRYPTO_3DES_CBC
                   CRYPTO_BLF_CBC
                   CRYPTO_CAST_CBC
                   CRYPTO_MD5_HMAC
                   CRYPTO_SHA1_HMAC
                   CRYPTO_RIPEMD160_HMAC
                   CRYPTO_MD5_KPDK
                   CRYPTO_SHA1_KPDK
                   CRYPTO_AES_CBC
                   CRYPTO_AES_CTR
                   CRYPTO_AES_XTS
                   CRYPTO_ARC4
                   CRYPTO_MD5
                   CRYPTO_SHA1

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

     cri_rnd       Specifies the number of rounds to be used with the algo-
                   rithm, 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 initial-
                   ization.  If no IV is explicitly passed (see below on
                   details), a random IV is used by the device driver process-
                   ing the request.

                   In the case of the CRYPTO_AES_XTS transform, the IV should
                   be provided as a 64-bit block number in host byte order.

     cri_next      Contains a pointer to another cryptoini structure.  Multi-
                   ple such structures may be linked to establish multi-algo-
                   rithm 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 length of the result, not includ-
                    ing crd_skip.  For symmetric crypto operations, this will
                    be the same as the input length.

     crp_alloctype  Indicates the type of buffer, as used in the kernel
                    malloc(9) routine.  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 appro-
                    priate 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.  Cur-
                    rently defined flags are:

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

     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 struct uio depend-
                    ing 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_skip    The offset in the input buffer where process-
                                ing should start.

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

                    crd_inject  Offset from the beginning of the buffer to
                                insert any results.  For encryption algo-
                                rithms, this is where the initialization vec-
                                tor (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
                                                   encryption is required
                                                   (when not set, decryption
                                                   is performed).

                                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 buf-
                                                   fer.  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 spe-
                                                   cial ``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 conjunc-
                                                   tion with the
                                                   CRD_F_IV_EXPLICIT flag.

                                CRD_F_IV_EXPLICIT  For encryption algorithms,
                                                   this bit is set when the IV
                                                   is explicitly provided by
                                                   the consumer in the crd_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 typically used when
                                                   the IV is calculated ``on
                                                   the fly'' by the consumer,
                                                   and does not precede the
                                                   data (some ipsec(4) config-
                                                   urations, and the encrypted
                                                   swap are two such exam-
                                                   ples).

                                CRD_F_COMP         For compression algorithms,
                                                   this bit is set when com-
                                                   pression 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 crypto-
                                graphic operation request, drivers may re-ini-
                                tialize state on-demand (typically an expen-
                                sive operation).  Furthermore, the crypto-
                                graphic 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 opera-
                                tions are useful in protocols such as
                                ipsec(4), where multiple cryptographic trans-
                                forms 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 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
                    there were lower level reasons for operation failure.

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

     krp_oparams    Number of 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-
                    ters.

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

     krp_callback   Callback called on completion of a keying operation.

DRIVER-SIDE API
     The crypto_get_driverid(), crypto_register(), crypto_kregister(),
     crypto_unregister(), 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 argument is the driver
     identifier.  The second argument is an array of CRYPTO_ALGORITHM_MAX + 1
     elements, indicating which algorithms are supported.  The last three
     arguments are pointers to three driver-provided functions that the frame-
     work 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.) 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(4) crypto cards that are being ejected will invoke this routine
     for all algorithms supported by the card.  If called with
     CRYPTO_ALGORITHM_ALL, all algorithms registered for a driver will be
     unregistered in one go 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) (u_int32_t *, struct cryptoini *);
     int (*freesession) (u_int64_t);
     int (*process) (struct cryptop *);
     int (*kprocess) (struct cryptkop *);

     On invocation, the first argument to newsession() contains the driver
     identifier obtained via crypto_get_driverid().  On successfully return-
     ing, it should contain a driver-specific session identifier.  The second
     argument is identical to that of crypto_newsession().

     The freesession() routine takes as argument the SID (which is the con-
     catenation of the driver identifier and the driver-specific session iden-
     tifier).  It should clear any context associated 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 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 previ-
     ously.

     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 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 invoke crypto_kdone().

RETURN VALUES
     crypto_register(), crypto_kregister(), crypto_unregister(),
     crypto_newsession(), and crypto_freesession() 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 other-
     wise.  The callback is provided with an error code in case of failure, in
     the crp_etype field.

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

SEE ALSO
     ipsec(4), pcmcia(4), malloc(9), tsleep(9)

HISTORY
     The cryptographic framework first appeared in OpenBSD 2.7 and was written
     by Angelos D. Keromytis <angelos@openbsd.org>.

BUGS
     The framework currently assumes that all the algorithms in a
     crypto_newsession() operation must be available by the same driver.  If
     that's 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
     request.

     A queue for completed operations should be implemented and processed at
     some software spl(9) level, to avoid overall system latency issues, and
     potential kernel stack exhaustion while processing a callback.

BSD                             August 20, 2014                            BSD