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CRYPTO(9) | Kernel Developer's Manual | CRYPTO(9) |
NAME¶
crypto
—
API for cryptographic services in the kernel
SYNOPSIS¶
#include
<opencrypto/cryptodev.h>
int32_t
crypto_get_driverid
(uint8_t);
int
crypto_register
(uint32_t,
int,
uint16_t,
uint32_t,
int (*)(void *,
uint32_t *, struct cryptoini *),
int (*)(void *,
uint64_t), int
(*)(void *, struct cryptop *),
void *);
int
crypto_kregister
(uint32_t,
int,
uint32_t,
int (*)(void *, struct
cryptkop *),
void *);
int
crypto_unregister
(uint32_t,
int);
int
crypto_unregister_all
(uint32_t);
void
crypto_done
(struct
cryptop *);
void
crypto_kdone
(struct
cryptkop *);
int
crypto_newsession
(uint64_t
*, struct
cryptoini *,
int);
int
crypto_freesession
(uint64_t);
int
crypto_dispatch
(struct
cryptop *);
int
crypto_kdispatch
(struct
cryptkop *);
int
crypto_unblock
(uint32_t,
int);
struct cryptop *
crypto_getreq
(int);
void
crypto_freereq
(void);
#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; uint64_t crp_sid; 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 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 (1) should be used or not (0). The various
fields in the cryptoini structure are:
- cri_alg
- Contains an algorithm identifier. Currently supported algorithms are:
CRYPTO_AES_CBC
CRYPTO_ARC4
CRYPTO_BLF_CBC
CRYPTO_CAMELLIA_CBC
CRYPTO_CAST_CBC
CRYPTO_DES_CBC
CRYPTO_3DES_CBC
CRYPTO_SKIPJACK_CBC
CRYPTO_MD5
CRYPTO_MD5_HMAC
CRYPTO_MD5_KPDK
CRYPTO_RIPEMD160_HMAC
CRYPTO_SHA1
CRYPTO_SHA1_HMAC
CRYPTO_SHA1_KPDK
CRYPTO_SHA2_256_HMAC
CRYPTO_SHA2_384_HMAC
CRYPTO_SHA2_512_HMAC
CRYPTO_NULL_HMAC
CRYPTO_NULL_CBC
- cri_klen
- Specifies the length of the key in bits, for variable-size key algorithms.
- cri_mlen
- Specifies how many bytes from the calculated hash should be copied back. 0 means entire hash.
- 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.
- 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).
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 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
- 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 ofcrypto_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.
CRYPTO_F_IOV
- The buffer pointed to by crp_buf is an uio structure.
CRYPTO_F_REL
- Must return data in the same place.
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.
- 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 contiguous buffer, 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_iv
- The field where IV should be provided when the
CRD_F_IV_EXPLICIT
flag is given. - crd_key
- When the
CRD_F_KEY_EXPLICIT
flag is given, 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
- 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 field. 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_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.
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 lower level reasons for operation failure.
- krp_iparams
- Number if input parameters to the specified operation. Note that each operation has a (typically hardwired) number of such parameters.
- krp_oparams
- Number if 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¶
Thecrypto_get_driverid
(),
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 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 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. The last four arguments must be
provided in the first call to
crypto_register
() and are ignored in all
subsequent calls. They 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.); and an opaque parameter to pass when calling each of
these routines. 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.
The calling convention for the three driver-supplied routines is:
- int
(*newsession)
(void *, uint32_t *, struct cryptoini *); - int
(*freesession)
(void *, uint64_t); - int
(*process)
(void *, struct cryptop *); - int
(*kprocess)
(void *, struct cryptkop *);
crypto_register
(). The second argument to
newsession
() contains the driver identifier
obtained via crypto_get_driverid
(). On
successful return, it should contain a driver-specific session identifier. The
third argument is identical to that of
crypto_newsession
().
The freesession
() routine takes as arguments
the opaque data value and 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 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 should 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¶
ipsec(4), 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 acrypto_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.
Note that 3DES is considered one algorithm (and not three instances of DES).
Thus, 3DES and DES could be mixed in the same request.September 19, 2007 | Debian |