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NAME
crypto — API for cryptographic services in the kernel
SYNOPSIS
#include <opencrypto/cryptodev.h>
int32_t
crypto_get_driverid(device_t dev, size_t session_size, int flags);
int
crypto_register(uint32_t driverid, int alg, uint16_t maxoplen, uint32_t flags);
int
crypto_kregister(uint32_t driverid, int kalg, uint32_t flags);
int
crypto_unregister(uint32_t driverid, int alg);
int
crypto_unregister_all(uint32_t driverid);
void
crypto_done(struct cryptop *crp);
void
crypto_kdone(struct cryptkop *krp);
int
crypto_find_driver(const char *match);
int
crypto_newsession(crypto_session_t *cses, struct cryptoini *cri, int crid);
int
crypto_freesession(crypto_session_t cses);
int
crypto_dispatch(struct cryptop *crp);
int
crypto_kdispatch(struct cryptkop *krp);
int
crypto_unblock(uint32_t driverid, int what);
struct cryptop *
crypto_getreq(int num);
void
crypto_freereq(struct cryptop *crp);
#define CRYPTO_SYMQ 0x1
#define CRYPTO_ASYMQ 0x2
#define EALG_MAX_BLOCK_LEN 16
struct cryptoini {
int cri_alg;
int cri_klen;
int cri_mlen;
caddr_t cri_key;
uint8_t cri_iv[EALG_MAX_BLOCK_LEN];
struct cryptoini *cri_next;
};
struct cryptodesc {
int crd_skip;
int crd_len;
int crd_inject;
int crd_flags;
struct cryptoini CRD_INI;
#define crd_iv CRD_INI.cri_iv
#define crd_key CRD_INI.cri_key
#define crd_alg CRD_INI.cri_alg
#define crd_klen CRD_INI.cri_klen
struct cryptodesc *crd_next;
};
struct cryptop {
TAILQ_ENTRY(cryptop) crp_next;
crypto_session_t crp_session;
int crp_ilen;
int crp_olen;
int crp_etype;
int crp_flags;
caddr_t crp_buf;
caddr_t crp_opaque;
struct cryptodesc *crp_desc;
int (*crp_callback) (struct cryptop *);
caddr_t crp_mac;
};
struct crparam {
caddr_t crp_p;
u_int crp_nbits;
};
#define CRK_MAXPARAM 8
struct cryptkop {
TAILQ_ENTRY(cryptkop) krp_next;
u_int krp_op; /* ie. CRK_MOD_EXP or other */
u_int krp_status; /* return status */
u_short krp_iparams; /* # of input parameters */
u_short krp_oparams; /* # of output parameters */
uint32_t krp_hid;
struct crparam krp_param[CRK_MAXPARAM];
int (*krp_callback)(struct cryptkop *);
};
DESCRIPTION
crypto is a framework for drivers of cryptographic hardware to register with the kernel so
“consumers” (other kernel subsystems, and users through the /dev/crypto device) are able to
make use of it. Drivers register with the framework the algorithms they support, and
provide entry points (functions) the framework may call to establish, use, and tear down
sessions. Sessions are used to cache cryptographic information in a particular driver (or
associated hardware), so initialization is not needed with every request. Consumers of
cryptographic services pass a set of descriptors that instruct the framework (and the
drivers registered with it) of the operations that should be applied on the data (more than
one cryptographic operation can be requested).
Keying operations are supported as well. Unlike the symmetric operators described above,
these sessionless commands perform mathematical operations using input and output
parameters.
Since the consumers may not be associated with a process, drivers may not sleep(9). The
same holds for the framework. Thus, a callback mechanism is used to notify a consumer that
a request has been completed (the callback is specified by the consumer on a per-request
basis). The callback is invoked by the framework whether the request was successfully
completed or not. An error indication is provided in the latter case. A specific error
code, EAGAIN, is used to indicate that a session handle has changed and that the request may
be re-submitted immediately with the new session. Errors are only returned to the invoking
function if not enough information to call the callback is available (meaning, there was a
fatal error in verifying the arguments). For session initialization and teardown no
callback mechanism is used.
The crypto_find_driver() returns the driver id of the device whose name matches match.
match can either be the exact name of a device including the unit or the driver name without
a unit. In the latter case, the id of the first device with the matching driver name is
returned. If no matching device is found, the value -1 is returned.
The crypto_newsession() routine is called by consumers of cryptographic services (such as
the ipsec(4) stack) that wish to establish a new session with the framework. The cri
argument points to a cryptoini structure containing all the necessary information for the
driver to establish the session. The crid argument is either a specific driver id or a
bitmask of flags. The flags are CRYPTOCAP_F_HARDWARE, to select hardware devices, or
CRYPTOCAP_F_SOFTWARE, to select software devices. If both are specified, hardware devices
are preferred over software devices. On success, the opaque session handle of the new
session will be stored in *cses. The cryptoini structure pointed to by cri contains these
fields:
cri_alg An algorithm identifier. Currently supported algorithms are:
CRYPTO_AES_128_NIST_GMAC
CRYPTO_AES_192_NIST_GMAC
CRYPTO_AES_256_NIST_GMAC
CRYPTO_AES_CBC
CRYPTO_AES_CCM_16
CRYPTO_AES_CCM_CBC_MAC
CRYPTO_AES_ICM
CRYPTO_AES_NIST_GCM_16
CRYPTO_AES_NIST_GMAC
CRYPTO_AES_XTS
CRYPTO_ARC4
CRYPTO_BLAKE2B
CRYPTO_BLAKE2S
CRYPTO_BLF_CBC
CRYPTO_CAMELLIA_CBC
CRYPTO_CAST_CBC
CRYPTO_CHACHA20
CRYPTO_DEFLATE_COMP
CRYPTO_DES_CBC
CRYPTO_3DES_CBC
CRYPTO_MD5
CRYPTO_MD5_HMAC
CRYPTO_MD5_KPDK
CRYPTO_NULL_HMAC
CRYPTO_NULL_CBC
CRYPTO_POLY1305
CRYPTO_RIPEMD160
CRYPTO_RIPEMD160_HMAC
CRYPTO_SHA1
CRYPTO_SHA1_HMAC
CRYPTO_SHA1_KPDK
CRYPTO_SHA2_224
CRYPTO_SHA2_224_HMAC
CRYPTO_SHA2_256
CRYPTO_SHA2_256_HMAC
CRYPTO_SHA2_384
CRYPTO_SHA2_384_HMAC
CRYPTO_SHA2_512
CRYPTO_SHA2_512_HMAC
CRYPTO_SKIPJACK_CBC
cri_klen For variable-size key algorithms, the length of the key in bits.
cri_mlen If non-zero, truncate the calculated hash to this many bytes.
cri_key The key to be used.
cri_iv An explicit initialization vector if it does not prefix the data. This field is
ignored during initialization (crypto_newsession). If no IV is explicitly passed
(see below on details), a random IV is used by the device driver processing the
request.
cri_next Pointer to another cryptoini structure. This is used to establish dual-algorithm
sessions, such as combining a cipher with a MAC.
The cryptoini structure and its contents will not be modified or referenced by the framework
or any cryptographic drivers. The memory associated with cri can be released once
crypto_newsession() returns.
crypto_freesession() is called with the session handle returned by crypto_newsession() to
free the session.
crypto_dispatch() is called to process a request. The various fields in the cryptop
structure are:
crp_session The session handle.
crp_ilen The total length in bytes of the buffer to be processed.
crp_olen On return, contains the total length of the result. For symmetric crypto
operations, this will be the same as the input length. This will be used if
the framework needs to allocate a new buffer for the result (or for re-
formatting the input).
crp_callback Callback routine invoked when a request is completed via crypto_done(). The
callback routine should inspect the crp_etype to determine if the request was
successfully completed.
crp_etype The error type, if any errors were encountered, or zero if the request was
successfully processed. If the EAGAIN error code is returned, the session
handle has changed (and has been recorded in the crp_session field). The
consumer should record the new session handle and use it in all subsequent
requests. In this case, the request may be re-submitted immediately. This
mechanism is used by the framework to perform session migration (move a
session from one driver to another, because of availability, performance, or
other considerations).
This field is only valid in the context of the callback routine specified by
crp_callback. Errors are returned to the invoker of crypto_process() only
when enough information is not present to call the callback routine (i.e., if
the pointer passed is NULL or if no callback routine was specified).
crp_flags A bitmask of flags associated with this request. Currently defined flags are:
CRYPTO_F_IMBUF The buffer is an mbuf chain pointed to by crp_mbuf.
CRYPTO_F_IOV The buffer is a uio structure pointed to by crp_uio.
CRYPTO_F_BATCH Batch operation if possible.
CRYPTO_F_CBIMM Do callback immediately instead of doing it from a
dedicated kernel thread.
CRYPTO_F_DONE Operation completed.
CRYPTO_F_CBIFSYNC Do callback immediately if operation is synchronous (that
the driver specified the CRYPTOCAP_F_SYNC flag).
CRYPTO_F_ASYNC Try to do the crypto operation in a pool of workers if the
operation is synchronous (that is, if the driver specified
the CRYPTOCAP_F_SYNC flag). It aims to speed up processing
by dispatching crypto operations on different processors.
CRYPTO_F_ASYNC_KEEPORDER
Dispatch callbacks in the same order they are posted. Only
relevant if the CRYPTO_F_ASYNC flag is set and if the
operation is synchronous.
crp_buf Data buffer unless CRYPTO_F_IMBUF or CRYPTO_F_IOV is set in crp_flags. The
length in bytes is set in crp_ilen.
crp_mbuf Data buffer mbuf chain when CRYPTO_F_IMBUF is set in crp_flags.
crp_uio struct uio data buffer when CRYPTO_F_IOV is set in crp_flags.
crp_opaque Cookie passed through the crypto framework untouched. It is intended for the
invoking application's use.
crp_desc A linked list of descriptors. Each descriptor provides information about what
type of cryptographic operation should be done on the input buffer. The
various fields are:
crd_iv When the flag CRD_F_IV_EXPLICIT is set, this field contains the
IV.
crd_key When the CRD_F_KEY_EXPLICIT flag is set, the crd_key points to a
buffer with encryption or authentication key.
crd_alg An algorithm to use. Must be the same as the one given at
newsession time.
crd_klen The crd_key key length.
crd_skip The offset in the input buffer where processing should start.
crd_len How many bytes, after crd_skip, should be processed.
crd_inject The crd_inject field specifies an offset in bytes from the
beginning of the buffer. For encryption algorithms, this may be
where the IV will be inserted when encrypting or where the IV may
be found for decryption (subject to crd_flags). For MAC
algorithms, this is where the result of the keyed hash will be
inserted.
crd_flags The following flags are defined:
CRD_F_ENCRYPT
For encryption algorithms, this bit is set when encryption is
required (when not set, decryption is performed).
CRD_F_IV_PRESENT
For encryption, if this bit is not set the IV used to encrypt
the packet will be written at the location pointed to by
crd_inject. The IV length is assumed to be equal to the
blocksize of the encryption algorithm. For encryption, if
this bit is set, nothing is done. For decryption, this flag
has no meaning. Applications that do special “IV cooking”,
such as the half-IV mode in ipsec(4), can use this flag to
indicate that the IV should not be written on the packet.
This flag is typically used in conjunction with the
CRD_F_IV_EXPLICIT flag.
CRD_F_IV_EXPLICIT
This bit is set when the IV is explicitly provided by the
consumer in the crd_iv field. Otherwise, for encryption
operations the IV is provided for by the driver used to
perform the operation, whereas for decryption operations the
offset of the IV is provided by the crd_inject field. This
flag is typically used when the IV is calculated “on the fly”
by the consumer, and does not precede the data.
CRD_F_KEY_EXPLICIT
For encryption and authentication (MAC) algorithms, this bit
is set when the key is explicitly provided by the consumer in
the crd_key field for the given operation. Otherwise, the
key is taken at newsession time from the cri_key field. As
calculating the key schedule may take a while, it is
recommended that often used keys are given their own session.
CRD_F_COMP
For compression algorithms, this bit is set when compression
is required (when not set, decompression is performed).
CRD_INI This cryptoini structure will not be modified by the framework or
the device drivers. Since this information accompanies every
cryptographic operation request, drivers may re-initialize state
on-demand (typically an expensive operation). Furthermore, the
cryptographic framework may re-route requests as a result of full
queues or hardware failure, as described above.
crd_next Point to the next descriptor. Linked operations are useful in
protocols such as ipsec(4), where multiple cryptographic
transforms may be applied on the same block of data.
crypto_getreq() allocates a cryptop structure with a linked list of num cryptodesc
structures.
crypto_freereq() deallocates a structure cryptop and any cryptodesc structures linked to it.
Note that it is the responsibility of the callback routine to do the necessary cleanups
associated with the opaque field in the cryptop structure.
crypto_kdispatch() is called to perform a keying operation. The various fields in the
cryptkop structure are:
krp_op Operation code, such as CRK_MOD_EXP.
krp_status Return code. This errno-style variable indicates whether lower level reasons
for operation failure.
krp_iparams Number of input parameters to the specified operation. Note that each
operation has a (typically hardwired) number of such parameters.
krp_oparams Number of output parameters from the specified operation. Note that each
operation has a (typically hardwired) number of such parameters.
krp_kvp An array of kernel memory blocks containing the parameters.
krp_hid Identifier specifying which low-level driver is being used.
krp_callback Callback called on completion of a keying operation.
DRIVER-SIDE API
The crypto_get_driverid(), crypto_get_driver_session(), crypto_register(),
crypto_kregister(), crypto_unregister(), crypto_unblock(), and crypto_done() routines are
used by drivers that provide support for cryptographic primitives to register and unregister
with the kernel crypto services framework.
Drivers must first use the crypto_get_driverid() function to acquire a driver identifier,
specifying the flags as an argument. One of CRYPTOCAP_F_SOFTWARE or CRYPTOCAP_F_HARDWARE
must be specified. The CRYPTOCAP_F_SYNC may also be specified, and should be specified if
the driver does all of it's operations synchronously. Drivers must pass the size of their
session structure as the second argument. An appropriately sized memory will be allocated
by the framework, zeroed, and passed to the driver's newsession() method.
For each algorithm the driver supports, it must then call crypto_register(). The first two
arguments are the driver and algorithm identifiers. The next two arguments specify the
largest possible operator length (in bits, important for public key operations) and flags
for this algorithm.
crypto_unregister() is called by drivers that wish to withdraw support for an algorithm.
The two arguments are the driver and algorithm identifiers, respectively. Typically,
drivers for PCMCIA crypto cards that are being ejected will invoke this routine for all
algorithms supported by the card. crypto_unregister_all() will unregister all algorithms
registered by a driver and the driver will be disabled (no new sessions will be allocated on
that driver, and any existing sessions will be migrated to other drivers). The same will be
done if all algorithms associated with a driver are unregistered one by one. After a call
to crypto_unregister_all() there will be no threads in either the newsession or freesession
function of the driver.
The calling convention for the driver-supplied routines are:
int (*newsession)(device_t, crypto_session_t, struct cryptoini *);
void (*freesession)(device_t, crypto_session_t);
int (*process)(device_t, struct cryptop *, int);
int (*kprocess)(device_t, struct cryptkop *, int);
On invocation, the first argument to all routines is the device_t that was provided to
crypto_get_driverid(). The second argument to newsession() is the opaque session handle for
the new session. The third argument is identical to that of crypto_newsession().
Drivers obtain a pointer to their session memory by invoking crypto_get_driver_session() on
the opaque crypto_session_t handle.
The freesession() routine takes as arguments the opaque data value and the session handle.
It should clear any context associated with the session (clear hardware registers, memory,
etc.). If no resources need to be released other than the contents of session memory, the
method is optional. The crypto framework will zero and release the allocated session memory
(after running the freesession() method, if one exists).
The process() routine is invoked with a request to perform crypto processing. This routine
must not block or sleep, but should queue the request and return immediately or process the
request to completion. In case of an unrecoverable error, the error indication must be
placed in the crp_etype field of the cryptop structure. When the request is completed, or
an error is detected, the process() routine must invoke crypto_done(). Session migration
may be performed, as mentioned previously.
In case of a temporary resource exhaustion, the process() routine may return ERESTART in
which case the crypto services will requeue the request, mark the driver as “blocked”, and
stop submitting requests for processing. The driver is then responsible for notifying the
crypto services when it is again able to process requests through the crypto_unblock()
routine. This simple flow control mechanism should only be used for short-lived resource
exhaustion as it causes operations to be queued in the crypto layer. Doing so is preferable
to returning an error in such cases as it can cause network protocols to degrade performance
by treating the failure much like a lost packet.
The kprocess() routine is invoked with a request to perform crypto key processing. This
routine must not block, but should queue the request and return immediately. Upon
processing the request, the callback routine should be invoked. In case of an unrecoverable
error, the error indication must be placed in the krp_status field of the cryptkop
structure. When the request is completed, or an error is detected, the kprocess() routine
should invoked crypto_kdone().
RETURN VALUES
crypto_register(), crypto_kregister(), crypto_unregister(), crypto_newsession(),
crypto_freesession(), and crypto_unblock() return 0 on success, or an error code on failure.
crypto_get_driverid() returns a non-negative value on error, and -1 on failure.
crypto_getreq() returns a pointer to a cryptop structure and NULL on failure.
crypto_dispatch() returns EINVAL if its argument or the callback function was NULL, and 0
otherwise. The callback is provided with an error code in case of failure, in the crp_etype
field.
FILES
sys/opencrypto/crypto.c most of the framework code
SEE ALSO
crypto(4), ipsec(4), crypto(7), malloc(9), sleep(9)
HISTORY
The cryptographic framework first appeared in OpenBSD 2.7 and was written by Angelos D.
Keromytis <angelos@openbsd.org>.
BUGS
The framework currently assumes that all the algorithms in a crypto_newsession() operation
must be available by the same driver. If that is not the case, session initialization will
fail.
The framework also needs a mechanism for determining which driver is best for a specific set
of algorithms associated with a session. Some type of benchmarking is in order here.
Multiple instances of the same algorithm in the same session are not supported.