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:
- Open a file descriptor for the device. See open(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. - Submit requests, synchronously with
CIOCCRYPT
(symmetric),CIOCCRYPTAEAD
(symmetric), orCIOCKEY
(asymmetric). - Destroy one session with
CIOCFSESSION
. - 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 */ };
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 # */ };
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; };
COP_ENCRYPT
. To decrypt, set cr_op->op toCOP_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 theCOP_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; };
CIOCCRYPTAEAD
is similar to theCIOCCRYPT
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; };
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; };
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.