crypto(9)

NAME

crypto - API for cryptographic services in the kernel

SYNOPSIS

#include <opencrypto/cryptodev.h>
int32_t
crypto_get_driverid(u_int8_t);
int
crypto_register(u_int32_t, int, u_int16_t, u_int32_t,
        int (*)(void *, u_int32_t *, struct cryptoini *),
        int (*)(void *, u_int64_t), int (*)(void  *,  struct
cryptop *),
        void *);
int
crypto_kregister(u_int32_t, int, u_int32_t,
        int (*)(void *, struct cryptkop *), 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 *);
int
crypto_unblock(u_int32_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_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 {
        TAILQ_ENTRY(cryptop) crp_next;
        u_int64_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  pa
rameters */
        u_short             krp_oparams;     /*  # of output
parameters */
        u_int32_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 in

formation in a
particular driver (or associated hardware), so initializa

tion is not
needed with every request. Consumers of cryptographic ser

vices 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 symmet

ric operators
described above, these sessionless commands perform mathe

matical 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 call

back mechanism
is used to notify a consumer that a request has been com

pleted (the callback is specified by the consumer on an per-request basis).

The callback
is invoked by the framework whether the request was success

fully completed or not. An error indication is provided in the lat

ter case. A
specific error code, EAGAIN, is used to indicate that a ses

sion number
has changed and that the request may be re-submitted immedi

ately with the
new session number. Errors are only returned to the invok

ing 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_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
CRYPTO_SHA2_HMAC
CRYPTO_NULL_HMAC
CRYPTO_NULL_CBC

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 algo

rithm.

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 struc

ture. Multi

ple such structures may be linked to establish

multi-algorithm sessions (ipsec(4) is an example con

sumer of such a
feature).

The cryptoini structure and its contents will not be modi

fied 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 vari

ous 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 rou

tine to set
the appropriate spl(9) level.

crp_etype Contains the error type, if any errors

were encoun

tered, or zero if the request was success

fully processed. If the EAGAIN error code is re

turned, 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 call

back 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 frame

work untouched

and is intended for the invoking applica

tion'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 algo

rithms, this
is where the result of the

keyed hash
will be inserted.

crd_flags The following flags are

defined:

CRD_F_ENCRYPT For

encryption

al

gorithms, this
bit

is set when
en

cryption is
re

quired (when
not

set, decryption

is performed).

CRD_F_IV_PRESENT For

encryption

al

gorithms, this
bit

is set when
the

IV already
pre

cedes the
da

ta, so the
crd_inject

value
will

be ignored
and

no IV will
be

written in
the

buffer.
Oth

erwise, the
IV

used to
en

crypt the
pack

et will be
writ

ten at the
lo

cation pointed
to

by
crd_inject.

The
IV

length is
as

sumed to be
equal

to the
block

size of the
en

cryption algorithm.

Some
ap

plications
that

do special
``IV

cooking'',
such

as the
half

IV mode in
ipsec(4),

can
use

this flag to
in

dicate that
the

IV should
not

be written
on

the packet.
This

flag is
typ

ically used
in

conjunction
with

the
CRD_F_IV_EX

PLICIT
flag.

CRD_F_IV_EXPLICIT For

encryption

al

gorithms, this
bit

is set when
the

IV is
ex

plicitly provid

ed by the
con

sumer in the
cri_iv

fields.
Oth

erwise, for
en

cryption operations

the IV is
pro

vided for by
the

driver used
to

perform the
op

eration,
where

as for
de

cryption operations

it is
point

ed to by
the

crd_inject
field.

This
flag

is typical

ly used when
the

IV is calculat

ed ``on the
fly''

by the
con

sumer, and
does

not precede
the

data (some
ipsec(4)

configura

tions, and
the

encrypted
swap

are two
such

examples).

CRD_F_COMP For

compression

al

gorithms, this
bit

is set when
com

pression is
re

quired (when
not

set, decompres

sion is performed).

CRD_INI This cryptoini structure

will not be

modified by the framework

or the device
drivers. Since this in

formation 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 descrip

tor. Linked

operations are useful in

protocols such
as ipsec(4), where multi

ple 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 speci

fied operation.

Note that each operation has a (typically

hardwired)
number of such parameters.

krp_oparams Number if output parameters from the

specified opera

tion. Note that each operation has a

(typically hardwired) number of such parameters.

krp_kvp An array of kernel memory blocks contain

ing the param

eters.

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(), crypto_unblock(), and crypto_done()

routines are
used by drivers that provide support for cryptographic prim

itives to register and unregister with the kernel crypto services frame

work. 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 identi

fiers. The next
two arguments specify the largest possible operator length

(in bits,
important for public key operations) and flags for this al

gorithm. 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 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.); 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 rou

tines is:

int (*newsession)(void *, u_int32_t *, struct cryptoini *);
int (*freesession)(void *, u_int64_t);
int (*process)(void *, struct cryptop *);
int (*kprocess)(void *, struct cryptkop *);

On invocation, the first argument to all routines is an

opaque data value
supplied when the algorithm is registered with

crypto_register(). The
second argument to newsession() contains the driver identi

fier 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 call

back 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 re

queue 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 mecha

nism should only
be used for short-lived resource exhaustion as it causes op

erations to be
queued in the crypto layer. Doing so is preferable to re

turning 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 detect

ed, 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 a
crypto_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.

BSD October 14, 2002

BSD