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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) 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.
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.