CRYPTO(4) NetBSD Kernel Interfaces Manual CRYPTO(4)
NAME
crypto, swcrypto -- user-mode access to hardware-accelerated cryptography
SYNOPSIS
hifn* at pci? dev ? function ? ubsec* at pci? dev ? function ? pseudo-device crypto pseudo-device swcrypto #include <sys/ioctl.h> #include <sys/time.h> #include <crypto/cryptodev.h>
DESCRIPTION
The crypto driver gives user-mode applications access to hardware-accel- erated cryptographic transforms, as implemented by the opencrypto(9) in- kernel interface. The swcrypto driver is a software-only implementation of the opencrypto(9) interface, and must be included to use the interface with- out hardware acceleration. The /dev/crypto special device provides an ioctl(2) based interface. User-mode applications should open the special device, then issue ioctl(2) calls on the descriptor. User-mode access to /dev/crypto is generally controlled by three sysctl(8) variables, kern.usercrypto, kern.userasymcrypto, and kern.cryptodevallowsoft. See sysctl(7) for additional details. The crypto device provides two distinct modes of operation: one mode for symmetric-keyed cryptographic requests, and a second mode for both asym- metric-key (public-key/private-key) requests, and for modular arithmetic (for Diffie-Hellman key exchange and other cryptographic protocols). The two modes are described separately below.
THEORY OF OPERATION
Regardless of whether symmetric-key or asymmetric-key operations are to be performed, use of the device requires a basic series of steps: 1. Open a file descriptor for the device. See open(2). 2. If any symmetric operation will be performed, create one session, with CIOCGSESSION, or multiple sessions, with CIOCNGSESSION. Most applications will require at least one symmetric session. Since cipher and MAC keys are tied to sessions, many applications will require more. Asymmetric operations do not use sessions. 3. Submit requests, synchronously with CIOCCRYPT (symmetric) or CIOCKEY (asymmetric) or asynchronously with CIOCNCRYPTM (symmetric) or CIOCNFKEYM (asymmetric). The asynchronous interface allows multiple requests to be submitted in one call if the user so desires. 4. If the asynchronous interface is used, wait for results with select(2) or poll(2), then collect them with CIOCNCRYPTRET (a par- ticular request) or CIOCNCRYPTRETM (multiple requests). 5. Destroy one session with CIOCFSESSION or many at once with CIOCNFSESSION. 6. Close the device with close(2).
SYMMETRIC-KEY OPERATION
The symmetric-key operation mode provides a context-based API to tradi- tional symmetric-key encryption (or privacy) algorithms, or to keyed and unkeyed one-way hash (HMAC and MAC) algorithms. The symmetric-key mode also permits fused operation, where the hardware performs both a privacy algorithm and an integrity-check algorithm in a single pass over the data: either a fused encrypt/HMAC-generate operation, or a fused HMAC- verify/decrypt operation. To use symmetric mode, you must first create a session specifying the algorithm(s) and key(s) to use; then issue encrypt or decrypt requests against the session. Symmetric-key privacy algorithms Contingent upon device drivers for installed cryptographic hardware reg- istering with opencrypto(9), as providers of a given algorithm, some or all of the following symmetric-key privacy algorithms may be available: CRYPTO_DES_CBC CRYPTO_3DES_CBC CRYPTO_BLF_CBC CRYPTO_CAST_CBC CRYPTO_SKIPJACK_CBC CRYPTO_AES_CBC CRYPTO_ARC4 Integrity-check operations Contingent upon hardware support, some or all of the following keyed one- way hash algorithms may be available: CRYPTO_RIPEMD160_HMAC CRYPTO_MD5_KPDK CRYPTO_SHA1_KPDK CRYPTO_MD5_HMAC CRYPTO_SHA1_HMAC CRYPTO_SHA2_256_HMAC CRYPTO_SHA2_384_HMAC CRYPTO_SHA2_512_HMAC CRYPTO_MD5 CRYPTO_SHA1 The CRYPTO_MD5 and CRYPTO_SHA1 algorithms are actually unkeyed, but should be requested as symmetric-key hash algorithms with a zero-length key. IOCTL Request Descriptions CRIOGET int *fd This operation is deprecated and will be removed after NetBSD 5.0. It clones the fd argument to ioctl(2), yielding a new file descriptor for the creation of sessions. Because the device now clones on open, this operation is unnecessary. CIOCGSESSION struct session_op *sessp struct session_op { u_int32_t cipher; /* e.g. CRYPTO_DES_CBC */ u_int32_t mac; /* e.g. CRYPTO_MD5_HMAC */ u_int32_t keylen; /* cipher key */ void * key; int mackeylen; /* mac key */ void * mackey; u_int32_t ses; /* returns: ses # */ }; Create a new cryptographic session on a file descriptor for the device; that is, a persistent object specific to the chosen pri- vacy algorithm, integrity algorithm, and keys specified in sessp. The special value 0 for either privacy or integrity is reserved to indicate that the indicated operation (privacy or integrity) is not desired for this session. Multiple sessions may be bound to a single file descriptor. The session ID returned in sessp->ses is supplied as a required field in the symmetric-operation structure crypt_op for future encryption or hashing requests. This implementation will never return a session ID of 0 for a successful creation of a session, which is a NetBSD extension. For non-zero symmetric-key privacy algorithms, the privacy algo- rithm must be specified in sessp->cipher, the key length in sessp->keylen, and the key value in the octets addressed by sessp->key. For keyed one-way hash algorithms, the one-way hash must be specified in sessp->mac, the key length in sessp->mackey, and the key value in the octets addressed by sessp->mackeylen. Support for a specific combination of fused privacy and integrity-check algorithms depends on whether the underlying hardware supports that combination. Not all combinations are supported by all hardware, even if the hardware supports each operation as a stand-alone non-fused operation. CIOCNGSESSION struct crypt_sgop *sgop struct crypt_sgop { size_t count; /* how many */ struct session_n_op * sessions; /* where to get them */ }; struct session_n_op { u_int32_t cipher; /* e.g. CRYPTO_DES_CBC */ u_int32_t mac; /* e.g. CRYPTO_MD5_HMAC */ u_int32_t keylen; /* cipher key */ void * key; u_int32_t mackeylen; /* mac key */ void * mackey; u_int32_t ses; /* returns: session # */ int status; }; Create one or more sessions. Takes a counted array of session_n_op structures in sgop. For each requested session (array element n), the session number is returned in sgop->sessions[n].ses and the status for that session creation in sgop->sessions[n].status. CIOCCRYPT struct crypt_op *cr_op struct crypt_op { u_int32_t ses; u_int16_t op; /* e.g. COP_ENCRYPT */ u_int16_t flags; u_int len; void * src, *dst; void * mac; /* must be large enough for result */ void * iv; }; Request a symmetric-key (or hash) operation. The file descrip- tor argument to ioctl(2) must have been bound to a valid ses- sion. To encrypt, set cr_op->op to COP_ENCRYPT. To decrypt, set cr_op->op to COP_DECRYPT. The field cr_op->len supplies the length of the input buffer; the fields cr_op->src, cr_op->dst, cr_op->mac, cr_op->iv supply the addresses of the input buffer, output buffer, one-way hash, and initialization vector, respec- tively. CIOCNCRYPTM struct crypt_mop *cr_mop struct crypt_mop { size_t count; /* how many */ struct crypt_n_op * reqs; /* where to get them */ }; struct crypt_n_op { u_int32_t ses; u_int16_t op; /* e.g. COP_ENCRYPT */ u_int16_t flags; u_int len; u_int32_t reqid; /* request id */ int status; /* accepted or not */ void *opaque; /* opaque pointer ret to user */ u_int32_t keylen; /* cipher key - optional */ void * key; u_int32_t mackeylen; /* mac key - optional */ void * mackey; void * src, * dst; void * mac; void * iv; }; This is the asynchronous version of CIOCCRYPT, which allows mul- tiple symmetric-key (or hash) operations to be started (see CIOCRYPT above for the details for each operation). The cr_mop->count field specifies the number of operations pro- vided in the cr_mop->reqs array. Each operation is assigned a unique request id returned in the cr_mop->reqs[n].reqid field. Each operation can accept an opaque value from the user to be passed back to the user when the operation completes (e.g., to track context for the request). The opaque field is cr_mop->reqs[n].opaque. If a problem occurs with starting any of the operations then that operation's cr_mop->reqs[n].status field is filled with the error code. The failure of an operation does not prevent the other operations from being started. The select(2) or poll(2) functions must be used on the device file descriptor to detect that some operation has completed; results are then retrieved with CIOCNCRYPTRETM. The key and mackey fields of the operation structure are cur- rently unused. They are intended for use to immediately rekey an existing session before processing a new request. CIOCFSESSION u_int32_t *ses_id Destroys the /dev/crypto session associated with the file- descriptor argument. CIOCNFSESSION struct crypt_sfop *sfop struct crypt_sfop { size_t count; u_int32_t *sesid; }; Destroys the sfop->count sessions specified by the sfop array of session identifiers.
ASYMMETRIC-KEY OPERATION
Asymmetric-key algorithms Contingent upon hardware support, the following asymmetric (public- key/private-key; or key-exchange subroutine) operations may also be available: Algorithm Input parameter Output parameter Count Count CRK_MOD_EXP 3 1 CRK_MOD_EXP_CRT 6 1 CRK_MOD_ADD 3 1 CRK_MOD_ADDINV 2 1 CRK_MOD_SUB 3 1 CRK_MOD_MULT 3 1 CRK_MOD_MULTINV 2 1 CRK_MOD 2 1 CRK_DSA_SIGN 5 2 CRK_DSA_VERIFY 7 0 CRK_DH_COMPUTE_KEY 3 1 See below for discussion of the input and output parameter counts. Asymmetric-key commands CIOCASYMFEAT int *feature_mask Returns a bitmask of supported asymmetric-key operations. Each of the above-listed asymmetric operations is present if and only if the bit position numbered by the code for that operation is set. For example, CRK_MOD_EXP is available if and only if the bit (1 << CRK_MOD_EXP) is set. CIOCKEY struct crypt_kop *kop struct crypt_kop { u_int crk_op; /* e.g. CRK_MOD_EXP */ u_int crk_status; /* return status */ u_short crk_iparams; /* # of input params */ u_short crk_oparams; /* # of output params */ u_int crk_pad1; struct crparam crk_param[CRK_MAXPARAM]; }; /* Bignum parameter, in packed bytes. */ struct crparam { void * crp_p; u_int crp_nbits; }; Performs an asymmetric-key operation from the list above. The specific operation is supplied in kop->crk_op; final status for the operation is returned in kop->crk_status. The number of input arguments and the number of output arguments is specified in kop->crk_iparams and kop->crk_iparams, respectively. The field crk_param[] must be filled in with exactly kop->crk_iparams + kop->crk_oparams arguments, each encoded as a struct crparam (address, bitlength) pair. The semantics of these arguments are currently undocumented. CIOCNFKEYM struct crypt_mkop *mkop struct crypt_mkop { size_t count; /* how many */ struct crypt_n_op * reqs; /* where to get them */ }; struct crypt_n_kop { u_int crk_op; /* e.g. CRK_MOD_EXP */ u_int crk_status; /* accepted or not */ u_short crk_iparams; /* # of input params */ u_short crk_oparams; /* # of output params */ u_int32_t crk_reqid; /* request id */ struct crparam crk_param[CRK_MAXPARAM]; void *crk_opaque; /* opaque pointer ret to user */ }; This is the asynchronous version of CIOCKEY, which starts one or more key operations. See CIOCNCRYPTM above and CIOCNCRYPTRETM below for descriptions of the mkop>count, mkop>reqs, mkop>reqs[n].crk_reqid, mkop>reqs[n].crk_status, and mkop>reqs[n].crk_opaque fields of the argument structure, and result retrieval. Asynchronous status commands When requests are submitted with the CIOCNCRYPTM or CIOCNFKEYM commands, result retrieval is asynchronous (the submit ioctls return immediately). Use the select(2) or poll(2) functions to determine when the file descriptor has completed operations ready to be retrieved. CIOCNCRYPTRET struct crypt_result *cres struct crypt_result { u_int32_t reqid; /* request ID */ u_int32_t status; /* 0 if successful */ void * opaque; /* pointer from user */ }; Check for the status of the request specified by cres->reqid. This requires a linear search through all completed requests and should be used with extreme care if the number of requests pend- ing on this file descriptor may be large. The cres->status field is set as follows: 0 The request has completed, and its results have been copied out to the original crypt_n_op or crypt_n_kop structure used to start the request. The copyout occurs during this ioctl, so the call- ing process must be the process that started the request. EINPROGRESS The request has not yet completed. EINVAL The request was not found. Other values indicate a problem during the processing of the request. CIOCNCRYPTRETM struct cryptret_t *cret struct cryptret { size_t count; /* space for how many */ struct crypt_result * results; /* where to put them */ }; Retrieve a number of completed requests. This ioctl accepts a count and an array (each array element is a crypt_result_t structure as used by CIOCNCRYPTRET above) and fills the array with up to cret->count results of completed requests. This ioctl fills in the cret->results[n].reqid field, so that the request which has completed may be identified by the appli- cation. Note that the results may include requests submitted both as symmetric and asymmetric operations.
SEE ALSO
hifn(4), ubsec(4), opencrypto(9)
HISTORY
The crypto driver is derived from a version which appeared in FreeBSD 4.8, which in turn is based on code which appeared in OpenBSD 3.2. The "new API" for asynchronous operation with multiple basic operations per system call (the "N" ioctl variants) was contributed by Coyote Point Systems, Inc. and first appeared in NetBSD 5.0.
BUGS
Error checking and reporting is weak. The values specified for symmetric-key key sizes to CIOCGSESSION must exactly match the values expected by opencrypto(9). The output buffer and MAC buffers supplied to CIOCCRYPT must follow whether privacy or integrity algorithms were specified for session: if you request a non-NULL algorithm, you must supply a suitably-sized buffer. The scheme for passing arguments for asymmetric requests is baroque. The naming inconsistency between CRIOGET and the various CIOC* names is an unfortunate historical artifact. NetBSD 8.0 January 27, 2014 NetBSD 8.0
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