CRYPTO(4)

CRYPTO(4) | Device Drivers 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-accelerated 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 special device, then issue ioctl(2) calls on the descriptor. User-mode access to /dev/crypto is generally controlled by three sysctl(8) variables, `kern.usercrypto`, `kern.userasymcrypto`, and `kern.cryptodevallowsoft`. See sysctl(7) for additional details.

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 `CIOCKEY` (asymmetric) or asynchronously with `CIOCNCRYPTM` (symmetric) or `CIOCNFKEYM` (asymmetric). The asynchronous interface allows multiple 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 particular 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 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.

## Symmetric-key privacy algorithms

Contingent upon device drivers for installed cryptographic hardware registering 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_256_HMAC
CRYPTO_SHA2_384_HMAC
CRYPTO_SHA2_512_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(2), 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 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.
`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 provided 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 currently unused. They are intended for use to immediately rekey an existing session before processing a new request.

`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_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 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.

`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 `CIOCKEY`, 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 calling 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 application. 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.

January 27, 2014 | NetBSD 11.0