[tahoe-dev] Running Tahoe on ARM plugs

Greg Troxel gdt at ir.bbn.com
Sun Feb 20 04:44:20 PST 2011


  > but unfortunately it
  > appears like the crypto processor is only accessible from kernel mode
  ...
  > so the distro, or the user, would
  > have to patch them in - and the number of people who are going to roll
  > their own custom patched kernel is pretty small compared to the number
  > of people who might theoretically want to run Tahoe on a plug).

  Well, if people aren't willing and able to do that, then they could
  run Davies-Meyer-AES-128 in software. I wonder how efficient that
  would be.

I don't quite follow how a device only being accessible from the kernel
(which is true for substantially all devices except perhaps via libusb)
leads to custom kernels, but presumably mainstream Linux maintenance is
unwilling to add support for these coprocessors.

This problem has been pretty much solved in *BSD, via the opencrypto
framework.  Each accelerator has a driver, there's a kernel-mode API,
user-space access to the operations, and integration with OpenSSL.
Support for AES and SHA-1 is usually better than for RSA within this
framework.

I just bought a Soekris net5501, and also the hifn-based crypto
coprocessor, so I'll see how well this works in practice.

http://portal.acm.org/citation.cfm?id=1250980
http://2009.asiabsdcon.org/papers/abc2009-P1B-paper.pdf


CRYPTO(4)               NetBSD Kernel Interfaces Manual              CRYPTO(4)

NAME
     crypto, swcrypto -- user-mode access to hardware-accelerated cryptography

SYNOPSIS
     hifn*   at pci? dev ? function ?
     ubsec*  at pci? dev ? function ?

     pseudo-device crypto
     pseudo-device swcrypto

     #include <sys/ioctl.h>
     #include <sys/time.h>
     #include <crypto/cryptodev.h>

DESCRIPTION
     The crypto driver gives user-mode applications access to hardware-accel-
     erated cryptographic transforms, as implemented by the opencrypto(9) in-
     kernel interface.  The swcrypto driver is a software-only implementation
     of the opencrypto(9) interface, and must be included to use the interface
     without hardware acceleration.  The /dev/crypto special device provides
     an ioctl(2) based interface.  User-mode applications should open the spe-
     cial device, then issue ioctl(2) calls on the descriptor.  The crypto
     device provides two distinct modes of operation: one mode for symmetric-
     keyed cryptographic requests, and a second mode for both asymmetric-key
     (public-key/private-key) requests, and for modular arithmetic (for
     Diffie-Hellman key exchange and other cryptographic protocols).  The two
     modes are described separately below.

THEORY OF OPERATION
     Regardless of whether symmetric-key or asymmetric-key operations are to
     be performed, use of the device requires a basic series of steps:

     1.   Open a file descriptor for the device.  See open(2).

     2.   If any symmetric operation will be performed, create one session,
          with CIOCGSESSION, or multiple sessions, with CIOCNGSESSION.  Most
          applications will require at least one symmetric session.  Since
          cipher and MAC keys are tied to sessions, many applications will
          require more.  Asymmetric operations do not use sessions.

     3.   Submit requests, synchronously with CIOCCRYPT (symmetric) or
          CIOCFKEY (asymmetric) or asynchronously with CIOCNCRYPTM (symmetric)
          or CIOCNFKEYM (asymmetric).  The asynchronous interface allows mul-
          tiple requests to be submitted in one call if the user so desires.

     4.   If the asynchronous interface is used, wait for results with
          select(2) or poll(2), then collect them with CIOCNCRYPTRET (a par-
          ticular request) or CIOCNCRYPTRETM (multiple requests).

     5.   Destroy one session with CIOCFSESSION or many at once with
          CIOCNFSESSION.

     6.   Close the device with close(2).

SYMMETRIC-KEY OPERATION
     The symmetric-key operation mode provides a context-based API to tradi-
     tional symmetric-key encryption (or privacy) algorithms, or to keyed and
     unkeyed one-way hash (HMAC and MAC) algorithms.  The symmetric-key mode
     also permits fused operation, where the hardware performs both a privacy
     algorithm and an integrity-check algorithm in a single pass over the
     data: either a fused encrypt/HMAC-generate operation, or a fused HMAC-
     verify/decrypt operation.

     To use symmetric mode, you must first create a session specifying the
     algorithm(s) and key(s) to use; then issue encrypt or decrypt requests
     against the session.

   Symmetric-key privacy algorithms
     Contingent upon device drivers for installed cryptographic hardware reg-
     istering with opencrypto(9), as providers of a given algorithm, some or
     all of the following symmetric-key privacy algorithms may be available:
           CRYPTO_DES_CBC
           CRYPTO_3DES_CBC
           CRYPTO_BLF_CBC
           CRYPTO_CAST_CBC
           CRYPTO_SKIPJACK_CBC
           CRYPTO_AES_CBC
           CRYPTO_ARC4

   Integrity-check operations
     Contingent upon hardware support, some or all of the following keyed one-
     way hash algorithms may be available:
           CRYPTO_RIPEMD160_HMAC
           CRYPTO_MD5_KPDK
           CRYPTO_SHA1_KPDK
           CRYPTO_MD5_HMAC
           CRYPTO_SHA1_HMAC
           CRYPTO_SHA2_HMAC
           CRYPTO_MD5
           CRYPTO_SHA1
     The CRYPTO_MD5 and CRYPTO_SHA1 algorithms are actually unkeyed, but
     should be requested as symmetric-key hash algorithms with a zero-length
     key.

   IOCTL Request Descriptions
     CRIOGET int *fd
               This operation is deprecated and will be removed after
               NetBSD 5.0. It clones the fd argument to ioctl(4), yielding a
               new file descriptor for the creation of sessions.  Because the
               device now clones on open, this operation is unnecessary.

     CIOCGSESSION struct session_op *sessp

               struct session_op {
                   u_int32_t cipher;   /* e.g. CRYPTO_DES_CBC */
                   u_int32_t mac;      /* e.g. CRYPTO_MD5_HMAC */

                   u_int32_t keylen;   /* cipher key */
                   void * key;
                   int mackeylen;      /* mac key */
                   void * mackey;

                   u_int32_t ses;      /* returns: ses # */
               };

               Create a new cryptographic session on a file descriptor for the
               device; that is, a persistent object specific to the chosen
               privacy algorithm, integrity algorithm, and keys specified in
               sessp.  The special value 0 for either privacy or integrity is
               reserved to indicate that the indicated operation (privacy or
               integrity) is not desired for this session.

               Multiple sessions may be bound to a single file descriptor.
               The session ID returned in sessp->ses is supplied as a required
               field in the symmetric-operation structure crypt_op for future
               encryption or hashing requests.

               This implementation will never return a session ID of 0 for a
               successful creation of a session, which is a NetBSD extension.

               For non-zero symmetric-key privacy algorithms, the privacy
               algorithm must be specified in sessp->cipher, the key length in
               sessp->keylen, and the key value in the octets addressed by
               sessp->key.

               For keyed one-way hash algorithms, the one-way hash must be
               specified in sessp->mac, the key length in sessp->mackey, and
               the key value in the octets addressed by sessp->mackeylen.

               Support for a specific combination of fused privacy  and
               integrity-check algorithms depends on whether the underlying
               hardware supports that combination.  Not all combinations are
               supported by all hardware, even if the hardware supports each
               operation as a stand-alone non-fused operation.

     CIOCNGSESSION struct crypt_sgop *sgop

               struct crypt_sgop {
                   size_t      count;                  /* how many */
                   struct session_n_op * sessions; /* where to get them */
               };

               struct session_n_op {
                   u_int32_t cipher;           /* e.g. CRYPTO_DES_CBC */
                   u_int32_t mac;              /* e.g. CRYPTO_MD5_HMAC */

                   u_int32_t keylen;           /* cipher key */
                   void * key;
                   u_int32_t mackeylen;        /* mac key */
                   void * mackey;

                   u_int32_t ses;              /* returns: session # */
                   int status;
               };

               Create one or more sessions.  Takes a counted array of
               session_n_op structures in sgop.  For each requested session
               (array element n), the session number is returned in
               sgop->sessions[n].ses and the status for that session creation
               in sgop->sessions[n].status.

     CIOCCRYPT struct crypt_op *cr_op

               struct crypt_op {
                   u_int32_t ses;
                   u_int16_t op;       /* e.g. COP_ENCRYPT */
                   u_int16_t flags;
                   u_int len;
                   void * src, *dst;
                   void * mac;         /* must be large enough for result */
                   void * iv;
               };

               Request a symmetric-key (or hash) operation.  The file descrip-
               tor argument to ioctl(4) must have been bound to a valid ses-
               sion.  To encrypt, set cr_op->op to COP_ENCRYPT.  To decrypt,
               set cr_op->op to COP_DECRYPT.  The field cr_op->len supplies
               the length of the input buffer; the fields cr_op->src,
               cr_op->dst, cr_op->mac, cr_op->iv supply the addresses of the
               input buffer, output buffer, one-way hash, and initialization
               vector, respectively.

     CIOCNCRYPTM struct crypt_mop *cr_mop

               struct crypt_mop {
                   size_t count;               /* how many */
                   struct crypt_n_op * reqs;   /* where to get them */
               };

               struct crypt_n_op {
                   u_int32_t ses;
                   u_int16_t op;               /* e.g. COP_ENCRYPT */
                   u_int16_t flags;
                   u_int len;

                   u_int32_t reqid;            /* request id */
                   int status;                 /* accepted or not */

                   void *opaque;               /* opaque pointer ret to user */
                   u_int32_t keylen;           /* cipher key - optional */
                   void * key;
                   u_int32_t mackeylen;        /* mac key - optional */
                   void * mackey;

                   void * src, * dst;
                   void * mac;
                   void * iv;
               };

               This is the asynchronous version of CIOCCRYPT, which allows
               multiple symmetric-key (or hash) operations to be started (see
               CIOCRYPT above for the details for each operation).

               The cr_mop->count field specifies the number of operations pro-
               vided in the cr_mop->reqs array.

               Each operation is assigned a unique request id returned in the
               cr_mop->reqs[n].reqid field.

               Each operation can accept an opaque value from the user to be
               passed back to the user when the operation completes ((e.g. to
               track context for the request).  The opaque field is
               cr_mop->reqs[n].opaque.

               If a problem occurs with starting any of the operations then
               that operation's cr_mop->reqs[n].status field is filled with
               the error code.  The failure of an operation does not prevent
               the other operations from being started.

               The select(2) or poll(2) functions must be used on the device
               file descriptor to detect that some operation has completed;
               results are then retrieved with CIOCNCRYPTRETM.

               The key and mackey fields of the operation structure are cur-
               rently unused.  They are intended for use to immediately rekey
               an existing session before processing a new request.

     CIOCFSESSION void
               Destroys the /dev/crypto session associated with the file-
               descriptor argument.

     CIOCNFSESSION struct crypt_sfop *sfop;

               struct crypt_sfop {
                   size_t count;
                   u_int32_t *sesid;
               };

               Destroys the sfop->count sessions specified by the sfop array
               of session identifiers.

ASYMMETRIC-KEY OPERATION
   Asymmetric-key algorithms
     Contingent upon hardware support, the following asymmetric (public-
     key/private-key; or key-exchange subroutine) operations may also be
     available:
           Algorithm             Input parameter    Output parameter
                                 Count              Count
           CRK_MOD_EXP           3                  1
           CRK_MOD_EXP_CRT       6                  1
           CRK_MOD_ADD           3                  1
           CRK_MOD_ADDINV        2                  1
           CRK_MOD_SUB           3                  1
           CRK_MOD_MULT          3                  1
           CRK_MOD_MULTINV       2                  1
           CRK_MOD               2                  1
           CRK_DSA_SIGN          5                  2
           CRK_DSA_VERIFY        7                  0
           CRK_DH_COMPUTE_KEY    3                  1

     See below for discussion of the input and output parameter counts.

   Asymmetric-key commands
     CIOCASYMFEAT int *feature_mask
               Returns a bitmask of supported asymmetric-key operations.  Each
               of the above-listed asymmetric operations is present if and
               only if the bit position numbered by the code for that opera-
               tion is set.  For example, CRK_MOD_EXP is available if and only
               if the bit (1 << CRK_MOD_EX) is set.

     CIOCFKEY struct crypt_kop *kop

               struct crypt_kop {
                   u_int crk_op;               /* e.g. CRK_MOD_EXP */
                   u_int crk_status;           /* return status */
                   u_short crk_iparams;        /* # of input params */
                   u_short crk_oparams;        /* # of output params */
                   u_int crk_pad1;
                   struct crparam crk_param[CRK_MAXPARAM];
               };

               /* Bignum parameter, in packed bytes. */
               struct crparam {
                   void * crp_p;
                   u_int crp_nbits;
               };

               Performs an asymmetric-key operation from the list above.  The
               specific operation is supplied in kop->crk_op; final status for
               the operation is returned in kop->crk_status.  The number of
               input arguments and the number of output arguments is specified
               in kop->crk_iparams and kop->crk_iparams, respectively.  The
               field crk_param[] must be filled in with exactly
               kop->crk_iparams + kop->crk_oparams arguments, each encoded as
               a struct crparam (address, bitlength) pair.

               The semantics of these arguments are currently undocumented.

     CIOCNFKEYM struct crypt_mkop *mkop

               struct crypt_mkop {
                   size_t count;               /* how many */
                   struct crypt_n_op * reqs;   /* where to get them */
               };

               struct crypt_n_kop {
                   u_int crk_op;               /* e.g. CRK_MOD_EXP */
                   u_int crk_status;           /* accepted or not */
                   u_short crk_iparams;        /* # of input params */
                   u_short crk_oparams;        /* # of output params */
                   u_int32_t crk_reqid;        /* request id */
                   struct crparam crk_param[CRK_MAXPARAM];
                   void *crk_opaque;           /* opaque pointer ret to user */
               };

               This is the asynchronous version of CIOCFKEY, which starts one
               or more key operations.  See CIOCNCRYPTM above and
               CIOCNCRYPTRETM below for descriptions of the mkop>count,
               mkop>reqs, mkop>reqs[n].crk_reqid, mkop>reqs[n].crk_status, and
               mkop>reqs[n].crk_opaque fields of the argument structure, and
               result retrieval.

   Asynchronous status commands
     When requests are submitted with the CIOCNCRYPTM or CIOCNFKEYM commands,
     result retrieval is asynchronous (the submit ioctls return immediately).
     Use the select(2) or poll(2) functions to determine when the file
     descriptor has completed operations ready to be retrieved.

     CIOCNCRYPTRET struct crypt_result *cres

               struct crypt_result {
                   u_int32_t reqid;    /* request ID */
                   u_int32_t status;   /* 0 if successful */
                   void * opaque;      /* pointer from user */
               };

               Check for the status of the request specified by cres->reqid.
               This requires a linear search through all completed requests
               and should be used with extreme care if the number of requests
               pending on this file descriptor may be large.

               The cres->status field is set as follows:

               0            The request has completed, and its results have
                            been copied out to the original crypt_n_op or
                            crypt_n_kop structure used to start the request.
                            The copyout occurs during this ioctl, so the call-
                            ing process must be the process that started the
                            request.

               EINPROGRESS  The request has not yet completed.

               EINVAL       The request was not found.

               Other values indicate a problem during the processing of the
               request.

     CIOCNCRYPTRETM struct cryptret_t *cret

               struct cryptret {
                   size_t count;                       /* space for how many */
                   struct crypt_result * results;      /* where to put them */
               };

               Retrieve a number of completed requests.  This ioctl accepts a
               count and an array (each array element is a crypt_result_t
               structure as used by CIOCNCRYPTRET above) and fills the array
               with up to cret->count results of completed requests.

               This ioctl fills in the cret->results[n].reqid field, so that
               the request which has completed may be identified by the appli-
               cation.  Note that the results may include requests submitted
               both as symmetric and asymmetric operations.

SEE ALSO
     hifn(4), ubsec(4), opencrypto(9)

HISTORY
     The crypto driver is derived from a version which appeared in
     FreeBSD 4.8, which in turn is based on code which appeared in
     OpenBSD 3.2.

     The "new API" for asynchronous operation with multiple basic operations
     per system call (the "N" ioctl variants) was contributed by Coyote Point
     Systems, Inc. and first appeared in NetBSD 5.0.

BUGS
     Error checking and reporting is weak.

     The values specified for symmetric-key key sizes to CIOCGSESSION must
     exactly match the values expected by opencrypto(9).  The output buffer
     and MAC buffers supplied to CIOCCRYPT must follow whether privacy or
     integrity algorithms were specified for session: if you request a
     non-NULL algorithm, you must supply a suitably-sized buffer.

     The scheme for passing arguments for asymmetric requests is Baroque.

     The naming inconsistency between CRIOGET and the various CIOC* names is
     an unfortunate historical artifact.

NetBSD 5.1                      March 29, 2008                      NetBSD 5.1



OPENCRYPTO(9)          NetBSD Kernel Developer's Manual          OPENCRYPTO(9)

NAME
     opencrypto, crypto_get_driverid, crypto_register, crypto_kregister,
     crypto_unregister, crypto_done, crypto_kdone, crypto_newsession,
     crypto_freesession, crypto_dispatch, crypto_kdispatch, crypto_getreq,
     crypto_freereq -- API for cryptographic services in the kernel

SYNOPSIS
     #include <opencrypto/cryptodev.h>

     int32_t
     crypto_get_driverid(u_int32_t);

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

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

     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;
             void            *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;
             void            *crp_buf;
             void            *crp_opaque;
             struct cryptodesc *crp_desc;
             int              (*crp_callback)(struct cryptop *);
             void            *crp_mac;
     };

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

DESCRIPTION
     opencrypto is a framework for drivers of cryptographic hardware to regis-
     ter with the kernel so ``consumers'' (other kernel subsystems, and even-
     tually users through an appropriate device) are able to make use of it.
     Drivers register with the framework the algorithms they support, and pro-
     vide entry points (functions) the framework may call to establish, use,
     and tear down sessions.  Sessions are used to cache cryptographic infor-
     mation 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 opera-
     tions using input and output parameters.

     Since the consumers may not be associated with a process, drivers may not
     use condition variables: condvar(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 an per-
     request basis).  The callback is invoked by the framework whether the
     request was successfully completed or not.  An error indication is pro-
     vided 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).  No callback mechanism is used for session initialization and
     teardown.

     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_SKIPJACK_CBC
                   CRYPTO_MD5_HMAC
                   CRYPTO_SHA1_HMAC
                   CRYPTO_RIPEMD160_HMAC
                   CRYPTO_MD5_KPDK
                   CRYPTO_SHA1_KPDK
                   CRYPTO_AES_CBC
                   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.

     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 including
                   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 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-
                   tions).

                   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
                                   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 contiguous buffer
                   (of a type identified by crp_alloctype), 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 process-
                                 ing 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 algo-
                                 rithms, this is where the initialization vec-
                                 tor (IV) will be inserted when encrypting or
                                 where it can be found when decrypting (sub-
                                 ject to crd_flags).  For MAC algorithms, this
                                 is where the result of the keyed hash will be
                                 inserted.

                   crd_flags     For adjusting general operation from user-
                                 land, 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 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 con-
                                                    junction 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 con-
                                                    sumer, and does not pre-
                                                    cede the data (some
                                                    ipsec(4) configurations,
                                                    and the encrypted swap are
                                                    two such examples).

                                 CRD_F_COMP         For compression algo-
                                                    rithms, this bit is set
                                                    when compression is
                                                    required (when not set,
                                                    decompression is per-
                                                    formed).

                   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 cryp-
                                 tographic 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 crytokop 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.

     The following sysctl entries exist to adjust the behaviour of the system
     from userland:

     kern.usercrypto          Allow (1) or forbid (0) userland acces to
                              /dev/crypto.

     kern.userasymcrypto      Allow (1) or forbid (0) userland acces to do
                              asymmetric crypto requests.

     kern.cryptodevallowsoft  Enable/disable access to hardware versus soft-
                              ware operations:

                              < 0  Force userlevel requests to use software
                                   operations, always.

                              = 0  Use hardware if present, grant userlevel
                                   requests for non-accelerated operations
                                   (handling the latter in software).

                              > 0  Allow user requests only for operations
                                   which are hardware-accelerated.

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 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) (void *, u_int32_t *, struct cryptoini *);
     int (*freesession) (void *, u_int64_t);
     int (*process) (void *, struct cryptop *, int);

     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.  The hint argument can
     be set to CRYPTO_HINT_MORE the there will be more request right after
     this request.  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.

     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/opencrypto/crypto.c  most of the framework code

     sys/crypto               crypto algorithm implementations

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

     Angelos D. Keromytis, Jason L. Wright, and Theo de Raadt, The Design of
     the OpenBSD Cryptographic Framework, Usenix, 2003, June 2003.

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

     Sam Leffler ported the crypto framework to FreeBSD and made performance
     improvements.

     Jonathan Stone <jonathan at NetBSD.org> ported the cryptoframe from FreeBSD
     to NetBSD.  opencrypto first appeared in NetBSD 2.0.

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.

     When SMP time comes, we will support use of a second processor (or more)
     as a crypto device (this is actually AMP, but we need the same basic sup-
     port).

NetBSD 5.1                      January 1, 2010                     NetBSD 5.1
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