OPENCRYPTO(9)

OPENCRYPTO(9) | Kernel Developer's Manual | OPENCRYPTO(9)

# NAME

opencrypto, crypto_get_driverid, crypto_register, crypto_kregister, crypto_unregister, crypto_unregister_all, 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);

int
crypto_unregister_all(u_int32_t);

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;         /* i.e. 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 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 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 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). 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 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_CAMELLIA_CBC
      CRYPTO_SKIPJACK_CBC
      CRYPTO_ARC4
      CRYPTO_AES_CBC
      CRYPTO_AES_CTR
      CRYPTO_AES_GCM_16
      CRYPTO_AES_GMAC
      CRYPTO_AES_128_GMAC
      CRYPTO_AES_192_GMAC
      CRYPTO_AES_256_GMAC
      CRYPTO_AES_XCBC_MAC_96
      CRYPTO_MD5
      CRYPTO_MD5_HMAC
      CRYPTO_MD5_HMAC_96
      CRYPTO_MD5_KPDK
      CRYPTO_NULL_CBC
      CRYPTO_NULL_HMAC
      CRYPTO_SHA1
      CRYPTO_SHA1_HMAC
      CRYPTO_SHA1_HMAC_96
      CRYPTO_SHA1_KPDK
      CRYPTO_SHA2_256_HMAC
      CRYPTO_SHA2_384_HMAC
      CRYPTO_SHA2_512_HMAC
      CRYPTO_RIPEMD160_HMAC
      CRYPTO_RIPEMD160_HMAC_96
      CRYPTO_DEFLATE_COMP
      CRYPTO_DEFLATE_COMP_NOGROW
      CRYPTO_GZIP_COMP

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.
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 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 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
    For adjusting general operation from userland, 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. 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 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) 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.

The following sysctl entries exist to adjust the behaviour of the system from userland:

kern.usercrypto
  Allow (1) or forbid (0) userland access to /dev/crypto.
kern.userasymcrypto
  Allow (1) or forbid (0) userland access to do asymmetric crypto requests.
kern.cryptodevallowsoft
  Enable/disable access to hardware versus software 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(), crypto_unregister_all(), 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 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. algorithms supported by the card. If all algorithms associated with a driver are unregistered, the driver will be disabled (no new sessions will be allocated on that driver, and any existing sessions will be migrated to other drivers). crypto_unregister_all() will unregister all registered algorithms, disable the driver, and migrate existing sessions to other drivers.

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 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. The hint argument can be set to CRYPTO_HINT_MORE when 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 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 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 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
sys/crypto
  crypto algorithm implementations

# SEE ALSO

ipsec(4), pcmcia(4), condvar(9), 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 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).

December 30, 2013 | NetBSD 7.1