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 open the special device and then issue ioctl(2) calls on the descriptor. User-mode access to /dev/crypto is controlled by the kern.cryptodevallowsoft sysctl(8) variable. If this variable is zero, then user-mode sessions are only permitted to use cryptography coprocessors.

THEORY OF OPERATION
Use of the device requires a basic series of steps:

1.  Open the /dev/crypto device.

2.  Create a session with CIOCGSESSION or CIOCGSESSION2. Applications will require at least one symmetric session. Since cipher and MAC keys are tied to sessions, many applications will require more.

3.  Submit requests, synchronously with CIOCCRYPT or CIOCCRYPTAEAD.

4.  Optionally destroy a session with CIOCFSESSION.

5.  Close the /dev/crypto device. This will automatically close any remaining sessions associated with the file desriptor.

SYMMETRIC-KEY OPERATION
cryptodev provides a context-based API to traditional symmetric-key encryption (or privacy) algorithms, keyed and unkeyed one-way hash (HMAC and MAC) algorithms, encrypt-then-authenticate (ETA) fused operations, and authenticated encryption with additional data (AEAD) operations. For ETA operations, drivers perform 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. Similarly, for AEAD operations, drivers perform either an encrypt/MAC-generate operation or a MAC-verify/decrypt operation.

The algorithm(s) and key(s) to use are specified when a session is created. Individual requests are able to specify per-request initialization vectors or nonces.

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

  IOCTL Request Descriptions

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 {
            uint32_t cipher;	/* e.g. CRYPTO_AES_CBC */
            uint32_t mac;	/* e.g. CRYPTO_SHA2_256_HMAC */
            uint32_t keylen;	/* cipher key */
            const void *key;
            int mackeylen;	/* mac key */
            const void *mackey;
            uint32_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. ETA sessions specify both privacy and integrity algorithms. AEAD sessions specify only a privacy algorithm.

    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 operation structure crypt_op for future encryption or hashing requests.

    For non-zero 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.

CIOCGSESSION2 struct session2_op *sessp

        struct session2_op {
            uint32_t cipher;	/* e.g. CRYPTO_AES_CBC */
            uint32_t mac;	/* e.g. CRYPTO_SHA2_256_HMAC */
            uint32_t keylen;	/* cipher key */
            const void *key;
            int mackeylen;	/* mac key */
            const void *mackey;
            uint32_t ses;	/* returns: ses # */
            int	crid;		/* driver id + flags (rw) */
            int ivlen;		/* length of nonce/IV */
            int maclen;		/* length of MAC/tag */
            int	pad[2];		/* for future expansion */
        };

    This request is similar to CIOGSESSION but adds additional fields.

    sessp-crid requests either a specific crypto device or a class of devices (software vs hardware).

    sessp-ivlen specifies the length of the IV or nonce supplied with each request. If this field is set to zero, the default IV or nonce length is used.

    sessp-maclen specifies the length of the MAC or authentication tag supplied or computed by each request. If this field is set to zero, the full MAC is used.

    The sessp-pad field must be initialized to zero.

CIOCCRYPT struct crypt_op *cr_op

        struct crypt_op {
            uint32_t ses;
            uint16_t op;	/* e.g. COP_ENCRYPT */
            uint16_t flags;
            u_int len;
            const void *src;
            void *dst;
            void *mac;		/* must be large enough for result */
            const void *iv;
        };

    Request an encryption/decryption (or hash) operation. 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 either fused encrypt-then-authenticate or an AEAD algorithm, decryption operations require the associated hash as an input. If the hash is incorrect, the operation will fail with EBADMSG and the output buffer will remain unchanged.

CIOCCRYPTAEAD struct crypt_aead *cr_aead

        struct crypt_aead {
            uint32_t ses;
            uint16_t op;	/* e.g. COP_ENCRYPT */
            uint16_t flags;
            u_int len;
            u_int aadlen;
            u_int ivlen;
            const void *src;
            void *dst;
            const void *aad;	/* additional authenticated data */
            void *tag;		/* must fit for chosen TAG length */
            const void *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 session identified by ses_id.

SEE ALSO
aesni(4), hifn(4), ipsec(4), padlock(4), safe(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.