OPENCRYPTO(9) NetBSD Kernel Developer's Manual OPENCRYPTO(9)
NAME
opencrypto, crypto_get_driverid, crypto_register, crypto_kregister, crypto_unregister, crypto_done, crypto_kdone, crypto_newsession, crypto_freesession, crypto_dispatch, crypto_kdispatch, crypto_getreq, crypto_freereq -- API for cryptographic services in the kernel
SYNOPSIS
#include <opencrypto/cryptodev.h> int32_t crypto_get_driverid(u_int32_t); int crypto_register(u_int32_t, int, u_int16_t, u_int32_t, int (*)(void *, u_int32_t *, struct cryptoini *), int (*)(void *, u_int32_t *), int (*)(u_int64_t), int (*)(struct cryptop *), void *); int crypto_kregister(u_int32_t, int, u_int32_t, int (*)(void *, struct cryptkop *, int), void *); 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; void *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 { TAILQ_ENTRY(cryptop) crp_next; u_int64_t crp_sid; int crp_ilen; int crp_olen; int crp_etype; int crp_flags; void *crp_buf; void *crp_opaque; struct cryptodesc *crp_desc; int (*crp_callback)(struct cryptop *); void *crp_mac; }; struct crparam { void *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 */ u_int32_t krp_hid; struct crparam krp_param[CRK_MAXPARAM]; /* kvm */ int (*krp_callback)(struct cryptkop *); };
DESCRIPTION
opencrypto is a framework for drivers of cryptographic hardware to regis- ter with the kernel so ``consumers'' (other kernel subsystems, and even- tually users through an appropriate device) are able to make use of it. Drivers register with the framework the algorithms they support, and pro- vide entry points (functions) the framework may call to establish, use, and tear down sessions. Sessions are used to cache cryptographic infor- mation 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 opera- tions using input and output parameters. Since the consumers may not be associated with a process, drivers may not use condition variables: condvar(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 an per- request basis). The callback is invoked by the framework whether the request was successfully completed or not. An error indication is pro- vided 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). No callback mechanism is used for session initialization and teardown. The crypto_newsession() routine is called by consumers of cryptographic services (such as the ipsec(4) stack) that wish to establish a new ses- sion 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_SKIPJACK_CBC CRYPTO_MD5_HMAC CRYPTO_SHA1_HMAC CRYPTO_RIPEMD160_HMAC CRYPTO_MD5_KPDK CRYPTO_SHA1_KPDK CRYPTO_AES_CBC 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 algo- rithm, 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 initial- ization. If no IV is explicitly passed (see below on details), a random IV is used by the device driver process- ing the request. cri_next Contains a pointer to another cryptoini structure. Multi- ple such structures may be linked to establish multi-algo- rithm 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 appropri- ate 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 considera- tions). 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 rou- tine (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. Cur- rently 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 contiguous buffer (of a type identified by crp_alloctype), 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 pro- vides information about what type of cryptographic opera- tion should be done on the input buffer. The various fields are: crd_skip The offset in the input buffer where process- ing 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 algo- rithms, this is where the initialization vec- tor (IV) will be inserted when encrypting or where it can be found when decrypting (sub- ject to crd_flags). For MAC algorithms, this is where the result of the keyed hash will be inserted. crd_flags For adjusting general operation from user- land, 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 con- junction 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 con- sumer, and does not pre- cede the data (some ipsec(4) configurations, and the encrypted swap are two such examples). CRD_F_COMP For compression algo- rithms, this bit is set when compression is required (when not set, decompression is per- formed). 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 cryp- tographic 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 opera- tions are useful in protocols such as ipsec(4), where multiple cryptographic trans- forms 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 call- back 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 crytokop 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) num- ber of such parameters. krp_oparams Number of output parameters from the specified operation. Note that each operation has a (typically hardwired) num- ber of such parameters. krp_kvp An array of kernel memory blocks containing the parame- ters. krp_hid Identifier specifying which low-level driver is being used. krp_callback Callback called on completion of a keying operation. The following sysctl entries exist to adjust the behaviour of the system from userland: kern.usercrypto Allow (1) or forbid (0) userland acces to /dev/crypto. kern.userasymcrypto Allow (1) or forbid (0) userland acces to do asymmetric crypto requests. kern.cryptodevallowsoft Enable/disable access to hardware versus soft- ware operations: < 0 Force userlevel requests to use software operations, always. = 0 Use hardware if present, grant userlevel requests for non-accelerated operations (handling the latter in software). > 0 Allow user requests only for operations which are hardware-accelerated.
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 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 frame- work 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) (void *, u_int32_t *, struct cryptoini *); int (*freesession) (void *, u_int64_t); int (*process) (void *, struct cryptop *, int); On invocation, the first argument to newsession() contains the driver identifier obtained via crypto_get_driverid(). On successfully return- ing, 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 con- catenation of the driver identifier and the driver-specific session iden- tifier). 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 pro- cessing. 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. The hint argument can be set to CRYPTO_HINT_MORE the there will be more request right after this request. 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 rou- tine 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 VALUES
crypto_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 other- wise. 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 sys/crypto crypto algorithm implementations
SEE ALSO
condvar(9), ipsec(4), pcmcia(4), malloc(9) Angelos D. Keromytis, Jason L. Wright, and Theo de Raadt, The Design of the OpenBSD Cryptographic Framework, Usenix, 2003, June 2003.
HISTORY
The cryptographic framework first appeared in OpenBSD 2.7 and was written by Angelos D. Keromytis <angelos@openbsd.org>. Sam Leffler ported the crypto framework to FreeBSD and made performance improvements. Jonathan Stone <jonathan@NetBSD.org> ported the cryptoframe from FreeBSD to NetBSD. opencrypto first appeared in NetBSD 2.0.
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 sup- ported. 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 sup- port). NetBSD 5.2 January 1, 2010 NetBSD 5.2
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