crypto

CRYPTO(4)                 BSD Kernel Interfaces Manual                 CRYPTO(4)

NAME
     crypto, cryptodev — user-mode access to hardware-accelerated cryptography

SYNOPSIS
     device crypto
     device cryptodev

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

DESCRIPTION
     The crypto driver gives user-mode applications access to hardware-
     accelerated cryptographic transforms, as implemented by the crypto(9) in-
     kernel interface.

     The /dev/crypto special device provides an ioctl(2) based interface.  User-
     mode applications should open the special device, then issue ioctl(2) calls
     on the descriptor.  User-mode access to /dev/crypto is controlled by three
     sysctl(8) variables, kern.userasymcrypto and kern.cryptodevallowsoft.

     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.  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),
          CIOCCRYPTAEAD (symmetric), or CIOCKEY (asymmetric).

     4.   Destroy one session with CIOCFSESSION.

     5.   Close the device with close(2).

SYMMETRIC-KEY OPERATION
     The symmetric-key operation mode provides a context-based API to
     traditional 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.

   Algorithms
     For a list of supported algorithms, see crypto(7) and crypto(9).

   IOCTL Request Descriptions
     CRIOGET int *fd
                   Clone the fd argument to ioctl(2), yielding a new file
                   descriptor for the creation of sessions.

     CIOCFINDDEV struct crypt_find_op *fop

                   struct crypt_find_op {
                       int     crid;       /* driver id + flags */
                       char    name[32];   /* device/driver name */
                   };

                   If crid is -1, then find the driver named name and return the
                   id in crid.  If crid is not -1, return the name of the driver
                   with crid in name.  In either case, if the driver is not
                   found, ENOENT is returned.

     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.

                   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.

     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;
                       caddr_t src, dst;
                       caddr_t mac;                /* must be large enough for result */
                       caddr_t iv;
                   };

                   Request a symmetric-key (or hash) operation.  The file
                   descriptor argument to ioctl(2) must have been bound to a
                   valid session.  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.  If a session is
                   using both a privacy algorithm and a hash algorithm, the
                   request will generate a hash of the input buffer before
                   generating the output buffer by default.  If the
                   COP_F_CIPHER_FIRST flag is included in the cr_op->flags
                   field, then the request will generate a hash of the output
                   buffer after executing the privacy algorithm.

     CIOCCRYPTAEAD struct crypt_aead *cr_aead

                   struct crypt_aead {
                       u_int32_t ses;
                       u_int16_t op;       /* e.g. COP_ENCRYPT */
                       u_int16_t flags;
                       u_int len;
                       u_int aadlen;
                       u_int ivlen;
                       caddr_t src, dst;
                       caddr_t aad;
                       caddr_t tag;                /* must be large enough for result */
                       caddr_t iv;
                   };

                   The CIOCCRYPTAEAD is similar to the CIOCCRYPT but provides
                   additional data in cr_aead->aad to include in the
                   authentication mode.

     CIOCFSESSION u_int32_t ses_id
                   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_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 operation is set.
              For example, CRK_MOD_EXP is available if and only if the bit (1 <<
              CRK_MOD_EXP) is set.

     CIOCKEY 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.

SEE ALSO
     aesni(4), hifn(4), ipsec(4), padlock(4), safe(4), ubsec(4), crypto(7),
     geli(8), crypto(9)

HISTORY
     The crypto driver first appeared in OpenBSD 3.0.  The crypto driver was
     imported to FreeBSD 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.

BSD                            September 21, 2017                            BSD