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_unregister
(u_int32_t,
int);
void
crypto_done
(struct
cryptop *);
int
crypto_newsession
(u_int64_t
*, struct cryptoini
*, int);
int
crypto_freesession
(u_int64_t);
int
crypto_dispatch
(struct
cryptop *);
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; };
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).
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_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 isNULL
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.
DRIVER-SIDE API
The
crypto_get_driverid
(),
crypto_register
(),
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 *);
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.
RETURN VALUES
crypto_register
(),
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 ALSO
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.