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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), 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;

void * key;

int mackeylen;

void * mackey;

u_int32_t 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;

u_int16_t flags;
u_int len;
caddr_t src, dst;

caddr_t mac;

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;

u_int16_t flags;
u_int len;
u_int aadlen;
u_int ivlen;
caddr_t src, dst;
caddr_t aad;

caddr_t tag;

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;

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