CRYPTO(9) OpenBSD Kernel Manual CRYPTO(9)NAME
crypto - API for cryptographic services in the kernel
SYNOPSIS
#include <crypto/cryptodev.h>
int32_t
crypto_get_driverid(u_int8_t);
int
crypto_register(u_int32_t, int *, int (*)(u_int32_t *, struct cryptoini
*), int (*)(u_int64_t), int (*)(struct cryptop *));
int
crypto_kregister(u_int32_t, int *, int (*)(struct cryptkop *));
int
crypto_unregister(u_int32_t, int);
void
crypto_done(struct cryptop *);
void
crypto_kdone(struct cryptkop *);
int
crypto_newsession(u_int64_t *, struct cryptoini *, int);
int
crypto_freesession(u_int64_t);
int
crypto_dispatch(struct cryptop *);
int
crypto_kdispatch(struct cryptkop *);
struct cryptop *
crypto_getreq(int);
void
crypto_freereq(struct cryptop *);
#define EALG_MAX_BLOCK_LEN 16
struct cryptoini {
int cri_alg;
int cri_klen;
int cri_rnd;
caddr_t cri_key;
u_int8_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;
struct cryptodesc *crd_next;
};
struct cryptop {
u_int64_t crp_sid;
int crp_ilen;
int crp_olen;
int crp_alloctype;
int crp_etype;
int crp_flags;
void *crp_buf;
void *crp_opaque;
struct cryptodesc *crp_desc;
int (*crp_callback)(struct cryptop *);
struct cryptop *crp_next;
caddr_t crp_mac;
};
struct crparam {
caddr_t crp_p;
u_int crp_nbits;
};
#define CRK_MAXPARAM 8
struct cryptkop {
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 */
u_int32_t krp_hid;
struct crparam krp_param[CRK_MAXPARAM]; /* kvm */
int (*krp_callback)(struct cryptkop *);
struct cryptkop *krp_next;
};
DESCRIPTION
crypto is a framework for drivers of cryptographic hardware to register
with the kernel so ``consumers'' (other kernel subsystems, and eventually
users through an appropriate 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
use tsleep(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 number
has changed and that the request may be re-submitted immediately with the
new session number. 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 there is no callback mechanism used.
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. On success, the first argument will contain
the Session Identifier (SID). The second argument contains all the
necessary information for the driver to establish the session. The third
argument indicates whether a hardware driver should be used (1) or not
(0). The various fields in the cryptoini structure are:
cri_alg Contains an algorithm identifier. Currently supported
algorithms are:
CRYPTO_DES_CBC
CRYPTO_3DES_CBC
CRYPTO_BLF_CBC
CRYPTO_CAST_CBC
CRYPTO_MD5_HMAC
CRYPTO_SHA1_HMAC
CRYPTO_RIPEMD160_HMAC
CRYPTO_MD5_KPDK
CRYPTO_SHA1_KPDK
CRYPTO_AES_CBC
CRYPTO_AES_CTR
CRYPTO_AES_XTS
CRYPTO_ARC4
CRYPTO_MD5
CRYPTO_SHA1
cri_klen Specifies the length of the key in bits, for variable-size
key algorithms.
cri_rnd Specifies the number of rounds to be used with the
algorithm, for variable-round algorithms.
cri_key Contains the key to be used with the algorithm.
cri_iv Contains an explicit initialization vector (IV), if it does
not prefix the data. This field is ignored during
initialization. If no IV is explicitly passed (see below
on details), a random IV is used by the device driver
processing the request.
In the case of the CRYPTO_AES_XTS transform, the IV should
be provided as a 64-bit block number in host byte order.
cri_next Contains a pointer to another cryptoini structure.
Multiple such structures may be linked to establish multi-
algorithm sessions (ipsec(4) is an example consumer of such
a feature).
The cryptoini structure and its contents will not be modified by the
framework (or the drivers used). Subsequent requests for processing that
use the SID returned will avoid the cost of re-initializing the hardware
(in essence, SID acts as an index in the session cache of the driver).
crypto_freesession() is called with the SID returned by
crypto_newsession() to disestablish the session.
crypto_dispatch() is called to process a request. The various fields in
the cryptop structure are:
crp_sid Contains the SID.
crp_ilen Indicates the total length in bytes of the buffer to be
processed.
crp_olen On return, contains the length of the result, not
including crd_skip. For symmetric crypto operations, this
will be the same as the input length.
crp_alloctype Indicates the type of buffer, as used in the kernel
malloc(9) routine. This will be used if the framework
needs to allocate a new buffer for the result (or for re-
formatting the input).
crp_callback This routine is invoked upon completion of the request,
whether successful or not. It is invoked through the
crypto_done() routine. If the request was not successful,
an error code is set in the crp_etype field. It is the
responsibility of the callback routine to set the
appropriate spl(9) level.
crp_etype Contains the error type, if any errors were encountered,
or zero if the request was successfully processed. If the
EAGAIN error code is returned, the SID has changed (and
has been recorded in the crp_sid field). The consumer
should record the new SID 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).
Note that this field only makes sense when examined by the
callback routine specified in 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 Is a bitmask of flags associated with this request.
Currently defined flags are:
CRYPTO_F_IMBUF The buffer pointed to by crp_buf is an
mbuf chain.
crp_buf Points to the input buffer. On return (when the callback
is invoked), it contains the result of the request. The
input buffer may be an mbuf chain or a struct uio
depending on crp_flags.
crp_opaque This is passed through the crypto framework untouched and
is intended for the invoking application's use.
crp_desc This is 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_skip The offset in the input buffer where
processing should start.
crd_len How many bytes, after crd_skip, should be
processed.
crd_inject Offset from the beginning of the buffer to
insert any results. For encryption
algorithms, this is where the initialization
vector (IV) will be inserted when encrypting
or where it can be found when decrypting
(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 algorithms,
this bit is set when the IV
already precedes the data,
so the crd_inject value
will be ignored and no IV
will be written in the
buffer. Otherwise, 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. Some
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 For encryption algorithms,
this bit is set when the IV
is explicitly provided by
the consumer in the crd_iv
fields. Otherwise, for
encryption operations the
IV is provided for by the
driver used to perform the
operation, whereas for
decryption operations it is
pointed to 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 (some ipsec(4)
configurations, and the
encrypted swap are two such
examples).
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 as
many cryptodesc structures as were specified in the argument passed to
it.
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
there were 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_register(), crypto_kregister(),
crypto_unregister(), 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 cc_flags as an argument (normally 0, but software-only drivers should
specify CRYPTOCAP_F_SOFTWARE). For each algorithm the driver supports,
it must then call crypto_register(). The first argument is the driver
identifier. The second argument is an array of CRYPTO_ALGORITHM_MAX + 1
elements, indicating which algorithms are supported. The last three
arguments are pointers to three driver-provided functions that the
framework may call to establish new cryptographic context with the
driver, free already established context, and ask for a request to be
processed (encrypt, decrypt, etc.) 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(4) crypto cards that are being ejected will
invoke this routine for all algorithms supported by the card. If called
with CRYPTO_ALGORITHM_ALL, all algorithms registered for a driver will be
unregistered in one go 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.
The calling convention for the three driver-supplied routines is:
int (*newsession) (u_int32_t *, struct cryptoini *);
int (*freesession) (u_int64_t);
int (*process) (struct cryptop *);
int (*kprocess) (struct cryptkop *);
On invocation, the first argument to newsession() contains the driver
identifier obtained via crypto_get_driverid(). On successfully
returning, it should contain a driver-specific session identifier. The
second argument is identical to that of crypto_newsession().
The freesession() routine takes as argument the SID (which is the
concatenation of the driver identifier and the driver-specific session
identifier). It should clear any context associated with the session
(clear hardware registers, memory, etc.).
The process() routine is invoked with a request to perform crypto
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 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
should invoke crypto_done(). Session migration may be performed, as
mentioned previously.
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 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 invoke crypto_kdone().
RETURN VALUEScrypto_register(), crypto_kregister(), crypto_unregister(),
crypto_newsession(), and crypto_freesession() 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/crypto/crypto.c most of the framework code
SEE ALSOipsec(4), pcmcia(4), malloc(9), tsleep(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's 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. Note that 3DES is considered one algorithm (and not three
instances of DES). Thus, 3DES and DES could be mixed in the same
request.
A queue for completed operations should be implemented and processed at
some software spl(9) level, to avoid overall system latency issues, and
potential kernel stack exhaustion while processing a callback.
When SMP time comes, we will support use of a second processor (or more)
as a crypto device (this is actually AMP, but we need the same basic
support).
OpenBSD 4.9 October 6, 2010 OpenBSD 4.9