diff options
Diffstat (limited to 'Documentation/crypto')
| -rw-r--r-- | Documentation/crypto/api-aead.rst | 23 | ||||
| -rw-r--r-- | Documentation/crypto/api-akcipher.rst | 20 | ||||
| -rw-r--r-- | Documentation/crypto/api-digest.rst | 35 | ||||
| -rw-r--r-- | Documentation/crypto/api-kpp.rst | 38 | ||||
| -rw-r--r-- | Documentation/crypto/api-rng.rst | 14 | ||||
| -rw-r--r-- | Documentation/crypto/api-samples.rst | 224 | ||||
| -rw-r--r-- | Documentation/crypto/api-skcipher.rst | 62 | ||||
| -rw-r--r-- | Documentation/crypto/api.rst | 25 | ||||
| -rw-r--r-- | Documentation/crypto/architecture.rst | 441 | ||||
| -rw-r--r-- | Documentation/crypto/devel-algos.rst | 247 | ||||
| -rw-r--r-- | Documentation/crypto/index.rst | 24 | ||||
| -rw-r--r-- | Documentation/crypto/intro.rst | 74 | ||||
| -rw-r--r-- | Documentation/crypto/userspace-if.rst | 387 |
13 files changed, 1614 insertions, 0 deletions
diff --git a/Documentation/crypto/api-aead.rst b/Documentation/crypto/api-aead.rst new file mode 100644 index 0000000..d15256f --- /dev/null +++ b/Documentation/crypto/api-aead.rst @@ -0,0 +1,23 @@ +Authenticated Encryption With Associated Data (AEAD) Algorithm Definitions +-------------------------------------------------------------------------- + +.. kernel-doc:: include/crypto/aead.h + :doc: Authenticated Encryption With Associated Data (AEAD) Cipher API + +.. kernel-doc:: include/crypto/aead.h + :functions: aead_request aead_alg + +Authenticated Encryption With Associated Data (AEAD) Cipher API +--------------------------------------------------------------- + +.. kernel-doc:: include/crypto/aead.h + :functions: crypto_alloc_aead crypto_free_aead crypto_aead_ivsize crypto_aead_authsize crypto_aead_blocksize crypto_aead_setkey crypto_aead_setauthsize crypto_aead_encrypt crypto_aead_decrypt + +Asynchronous AEAD Request Handle +-------------------------------- + +.. kernel-doc:: include/crypto/aead.h + :doc: Asynchronous AEAD Request Handle + +.. kernel-doc:: include/crypto/aead.h + :functions: crypto_aead_reqsize aead_request_set_tfm aead_request_alloc aead_request_free aead_request_set_callback aead_request_set_crypt aead_request_set_ad diff --git a/Documentation/crypto/api-akcipher.rst b/Documentation/crypto/api-akcipher.rst new file mode 100644 index 0000000..40aa874 --- /dev/null +++ b/Documentation/crypto/api-akcipher.rst @@ -0,0 +1,20 @@ +Asymmetric Cipher Algorithm Definitions +--------------------------------------- + +.. kernel-doc:: include/crypto/akcipher.h + :functions: akcipher_alg akcipher_request + +Asymmetric Cipher API +--------------------- + +.. kernel-doc:: include/crypto/akcipher.h + :doc: Generic Public Key API + +.. kernel-doc:: include/crypto/akcipher.h + :functions: crypto_alloc_akcipher crypto_free_akcipher crypto_akcipher_set_pub_key crypto_akcipher_set_priv_key crypto_akcipher_maxsize crypto_akcipher_encrypt crypto_akcipher_decrypt crypto_akcipher_sign crypto_akcipher_verify + +Asymmetric Cipher Request Handle +-------------------------------- + +.. kernel-doc:: include/crypto/akcipher.h + :functions: akcipher_request_alloc akcipher_request_free akcipher_request_set_callback akcipher_request_set_crypt diff --git a/Documentation/crypto/api-digest.rst b/Documentation/crypto/api-digest.rst new file mode 100644 index 0000000..07356fa --- /dev/null +++ b/Documentation/crypto/api-digest.rst @@ -0,0 +1,35 @@ +Message Digest Algorithm Definitions +------------------------------------ + +.. kernel-doc:: include/crypto/hash.h + :doc: Message Digest Algorithm Definitions + +.. kernel-doc:: include/crypto/hash.h + :functions: hash_alg_common ahash_alg shash_alg + +Asynchronous Message Digest API +------------------------------- + +.. kernel-doc:: include/crypto/hash.h + :doc: Asynchronous Message Digest API + +.. kernel-doc:: include/crypto/hash.h + :functions: crypto_alloc_ahash crypto_free_ahash crypto_ahash_init crypto_ahash_digestsize crypto_ahash_reqtfm crypto_ahash_reqsize crypto_ahash_setkey crypto_ahash_finup crypto_ahash_final crypto_ahash_digest crypto_ahash_export crypto_ahash_import + +Asynchronous Hash Request Handle +-------------------------------- + +.. kernel-doc:: include/crypto/hash.h + :doc: Asynchronous Hash Request Handle + +.. kernel-doc:: include/crypto/hash.h + :functions: ahash_request_set_tfm ahash_request_alloc ahash_request_free ahash_request_set_callback ahash_request_set_crypt + +Synchronous Message Digest API +------------------------------ + +.. kernel-doc:: include/crypto/hash.h + :doc: Synchronous Message Digest API + +.. kernel-doc:: include/crypto/hash.h + :functions: crypto_alloc_shash crypto_free_shash crypto_shash_blocksize crypto_shash_digestsize crypto_shash_descsize crypto_shash_setkey crypto_shash_digest crypto_shash_export crypto_shash_import crypto_shash_init crypto_shash_update crypto_shash_final crypto_shash_finup diff --git a/Documentation/crypto/api-kpp.rst b/Documentation/crypto/api-kpp.rst new file mode 100644 index 0000000..7d86ab9 --- /dev/null +++ b/Documentation/crypto/api-kpp.rst @@ -0,0 +1,38 @@ +Key-agreement Protocol Primitives (KPP) Cipher Algorithm Definitions +-------------------------------------------------------------------- + +.. kernel-doc:: include/crypto/kpp.h + :functions: kpp_request crypto_kpp kpp_alg kpp_secret + +Key-agreement Protocol Primitives (KPP) Cipher API +-------------------------------------------------- + +.. kernel-doc:: include/crypto/kpp.h + :doc: Generic Key-agreement Protocol Primitives API + +.. kernel-doc:: include/crypto/kpp.h + :functions: crypto_alloc_kpp crypto_free_kpp crypto_kpp_set_secret crypto_kpp_generate_public_key crypto_kpp_compute_shared_secret crypto_kpp_maxsize + +Key-agreement Protocol Primitives (KPP) Cipher Request Handle +------------------------------------------------------------- + +.. kernel-doc:: include/crypto/kpp.h + :functions: kpp_request_alloc kpp_request_free kpp_request_set_callback kpp_request_set_input kpp_request_set_output + +ECDH Helper Functions +--------------------- + +.. kernel-doc:: include/crypto/ecdh.h + :doc: ECDH Helper Functions + +.. kernel-doc:: include/crypto/ecdh.h + :functions: ecdh crypto_ecdh_key_len crypto_ecdh_encode_key crypto_ecdh_decode_key + +DH Helper Functions +------------------- + +.. kernel-doc:: include/crypto/dh.h + :doc: DH Helper Functions + +.. kernel-doc:: include/crypto/dh.h + :functions: dh crypto_dh_key_len crypto_dh_encode_key crypto_dh_decode_key diff --git a/Documentation/crypto/api-rng.rst b/Documentation/crypto/api-rng.rst new file mode 100644 index 0000000..10ba743 --- /dev/null +++ b/Documentation/crypto/api-rng.rst @@ -0,0 +1,14 @@ +Random Number Algorithm Definitions +----------------------------------- + +.. kernel-doc:: include/crypto/rng.h + :functions: rng_alg + +Crypto API Random Number API +---------------------------- + +.. kernel-doc:: include/crypto/rng.h + :doc: Random number generator API + +.. kernel-doc:: include/crypto/rng.h + :functions: crypto_alloc_rng crypto_rng_alg crypto_free_rng crypto_rng_generate crypto_rng_get_bytes crypto_rng_reset crypto_rng_seedsize diff --git a/Documentation/crypto/api-samples.rst b/Documentation/crypto/api-samples.rst new file mode 100644 index 0000000..0a10819 --- /dev/null +++ b/Documentation/crypto/api-samples.rst @@ -0,0 +1,224 @@ +Code Examples +============= + +Code Example For Symmetric Key Cipher Operation +----------------------------------------------- + +:: + + + struct tcrypt_result { + struct completion completion; + int err; + }; + + /* tie all data structures together */ + struct skcipher_def { + struct scatterlist sg; + struct crypto_skcipher *tfm; + struct skcipher_request *req; + struct tcrypt_result result; + }; + + /* Callback function */ + static void test_skcipher_cb(struct crypto_async_request *req, int error) + { + struct tcrypt_result *result = req->data; + + if (error == -EINPROGRESS) + return; + result->err = error; + complete(&result->completion); + pr_info("Encryption finished successfully\n"); + } + + /* Perform cipher operation */ + static unsigned int test_skcipher_encdec(struct skcipher_def *sk, + int enc) + { + int rc = 0; + + if (enc) + rc = crypto_skcipher_encrypt(sk->req); + else + rc = crypto_skcipher_decrypt(sk->req); + + switch (rc) { + case 0: + break; + case -EINPROGRESS: + case -EBUSY: + rc = wait_for_completion_interruptible( + &sk->result.completion); + if (!rc && !sk->result.err) { + reinit_completion(&sk->result.completion); + break; + } + default: + pr_info("skcipher encrypt returned with %d result %d\n", + rc, sk->result.err); + break; + } + init_completion(&sk->result.completion); + + return rc; + } + + /* Initialize and trigger cipher operation */ + static int test_skcipher(void) + { + struct skcipher_def sk; + struct crypto_skcipher *skcipher = NULL; + struct skcipher_request *req = NULL; + char *scratchpad = NULL; + char *ivdata = NULL; + unsigned char key[32]; + int ret = -EFAULT; + + skcipher = crypto_alloc_skcipher("cbc-aes-aesni", 0, 0); + if (IS_ERR(skcipher)) { + pr_info("could not allocate skcipher handle\n"); + return PTR_ERR(skcipher); + } + + req = skcipher_request_alloc(skcipher, GFP_KERNEL); + if (!req) { + pr_info("could not allocate skcipher request\n"); + ret = -ENOMEM; + goto out; + } + + skcipher_request_set_callback(req, CRYPTO_TFM_REQ_MAY_BACKLOG, + test_skcipher_cb, + &sk.result); + + /* AES 256 with random key */ + get_random_bytes(&key, 32); + if (crypto_skcipher_setkey(skcipher, key, 32)) { + pr_info("key could not be set\n"); + ret = -EAGAIN; + goto out; + } + + /* IV will be random */ + ivdata = kmalloc(16, GFP_KERNEL); + if (!ivdata) { + pr_info("could not allocate ivdata\n"); + goto out; + } + get_random_bytes(ivdata, 16); + + /* Input data will be random */ + scratchpad = kmalloc(16, GFP_KERNEL); + if (!scratchpad) { + pr_info("could not allocate scratchpad\n"); + goto out; + } + get_random_bytes(scratchpad, 16); + + sk.tfm = skcipher; + sk.req = req; + + /* We encrypt one block */ + sg_init_one(&sk.sg, scratchpad, 16); + skcipher_request_set_crypt(req, &sk.sg, &sk.sg, 16, ivdata); + init_completion(&sk.result.completion); + + /* encrypt data */ + ret = test_skcipher_encdec(&sk, 1); + if (ret) + goto out; + + pr_info("Encryption triggered successfully\n"); + + out: + if (skcipher) + crypto_free_skcipher(skcipher); + if (req) + skcipher_request_free(req); + if (ivdata) + kfree(ivdata); + if (scratchpad) + kfree(scratchpad); + return ret; + } + + +Code Example For Use of Operational State Memory With SHASH +----------------------------------------------------------- + +:: + + + struct sdesc { + struct shash_desc shash; + char ctx[]; + }; + + static struct sdescinit_sdesc(struct crypto_shash *alg) + { + struct sdescsdesc; + int size; + + size = sizeof(struct shash_desc) + crypto_shash_descsize(alg); + sdesc = kmalloc(size, GFP_KERNEL); + if (!sdesc) + return ERR_PTR(-ENOMEM); + sdesc->shash.tfm = alg; + sdesc->shash.flags = 0x0; + return sdesc; + } + + static int calc_hash(struct crypto_shashalg, + const unsigned chardata, unsigned int datalen, + unsigned chardigest) { + struct sdescsdesc; + int ret; + + sdesc = init_sdesc(alg); + if (IS_ERR(sdesc)) { + pr_info("trusted_key: can't alloc %s\n", hash_alg); + return PTR_ERR(sdesc); + } + + ret = crypto_shash_digest(&sdesc->shash, data, datalen, digest); + kfree(sdesc); + return ret; + } + + +Code Example For Random Number Generator Usage +---------------------------------------------- + +:: + + + static int get_random_numbers(u8 *buf, unsigned int len) + { + struct crypto_rngrng = NULL; + chardrbg = "drbg_nopr_sha256"; /* Hash DRBG with SHA-256, no PR */ + int ret; + + if (!buf || !len) { + pr_debug("No output buffer provided\n"); + return -EINVAL; + } + + rng = crypto_alloc_rng(drbg, 0, 0); + if (IS_ERR(rng)) { + pr_debug("could not allocate RNG handle for %s\n", drbg); + return -PTR_ERR(rng); + } + + ret = crypto_rng_get_bytes(rng, buf, len); + if (ret < 0) + pr_debug("generation of random numbers failed\n"); + else if (ret == 0) + pr_debug("RNG returned no data"); + else + pr_debug("RNG returned %d bytes of data\n", ret); + + out: + crypto_free_rng(rng); + return ret; + } diff --git a/Documentation/crypto/api-skcipher.rst b/Documentation/crypto/api-skcipher.rst new file mode 100644 index 0000000..b20028a --- /dev/null +++ b/Documentation/crypto/api-skcipher.rst @@ -0,0 +1,62 @@ +Block Cipher Algorithm Definitions +---------------------------------- + +.. kernel-doc:: include/linux/crypto.h + :doc: Block Cipher Algorithm Definitions + +.. kernel-doc:: include/linux/crypto.h + :functions: crypto_alg ablkcipher_alg blkcipher_alg cipher_alg + +Symmetric Key Cipher API +------------------------ + +.. kernel-doc:: include/crypto/skcipher.h + :doc: Symmetric Key Cipher API + +.. kernel-doc:: include/crypto/skcipher.h + :functions: crypto_alloc_skcipher crypto_free_skcipher crypto_has_skcipher crypto_skcipher_ivsize crypto_skcipher_blocksize crypto_skcipher_setkey crypto_skcipher_reqtfm crypto_skcipher_encrypt crypto_skcipher_decrypt + +Symmetric Key Cipher Request Handle +----------------------------------- + +.. kernel-doc:: include/crypto/skcipher.h + :doc: Symmetric Key Cipher Request Handle + +.. kernel-doc:: include/crypto/skcipher.h + :functions: crypto_skcipher_reqsize skcipher_request_set_tfm skcipher_request_alloc skcipher_request_free skcipher_request_set_callback skcipher_request_set_crypt + +Single Block Cipher API +----------------------- + +.. kernel-doc:: include/linux/crypto.h + :doc: Single Block Cipher API + +.. kernel-doc:: include/linux/crypto.h + :functions: crypto_alloc_cipher crypto_free_cipher crypto_has_cipher crypto_cipher_blocksize crypto_cipher_setkey crypto_cipher_encrypt_one crypto_cipher_decrypt_one + +Asynchronous Block Cipher API - Deprecated +------------------------------------------ + +.. kernel-doc:: include/linux/crypto.h + :doc: Asynchronous Block Cipher API + +.. kernel-doc:: include/linux/crypto.h + :functions: crypto_free_ablkcipher crypto_has_ablkcipher crypto_ablkcipher_ivsize crypto_ablkcipher_blocksize crypto_ablkcipher_setkey crypto_ablkcipher_reqtfm crypto_ablkcipher_encrypt crypto_ablkcipher_decrypt + +Asynchronous Cipher Request Handle - Deprecated +----------------------------------------------- + +.. kernel-doc:: include/linux/crypto.h + :doc: Asynchronous Cipher Request Handle + +.. kernel-doc:: include/linux/crypto.h + :functions: crypto_ablkcipher_reqsize ablkcipher_request_set_tfm ablkcipher_request_alloc ablkcipher_request_free ablkcipher_request_set_callback ablkcipher_request_set_crypt + +Synchronous Block Cipher API - Deprecated +----------------------------------------- + +.. kernel-doc:: include/linux/crypto.h + :doc: Synchronous Block Cipher API + +.. kernel-doc:: include/linux/crypto.h + :functions: crypto_alloc_blkcipher rypto_free_blkcipher crypto_has_blkcipher crypto_blkcipher_name crypto_blkcipher_ivsize crypto_blkcipher_blocksize crypto_blkcipher_setkey crypto_blkcipher_encrypt crypto_blkcipher_encrypt_iv crypto_blkcipher_decrypt crypto_blkcipher_decrypt_iv crypto_blkcipher_set_iv crypto_blkcipher_get_iv diff --git a/Documentation/crypto/api.rst b/Documentation/crypto/api.rst new file mode 100644 index 0000000..2e51919 --- /dev/null +++ b/Documentation/crypto/api.rst @@ -0,0 +1,25 @@ +Programming Interface +===================== + +Please note that the kernel crypto API contains the AEAD givcrypt API +(crypto_aead_giv\* and aead_givcrypt\* function calls in +include/crypto/aead.h). This API is obsolete and will be removed in the +future. To obtain the functionality of an AEAD cipher with internal IV +generation, use the IV generator as a regular cipher. For example, +rfc4106(gcm(aes)) is the AEAD cipher with external IV generation and +seqniv(rfc4106(gcm(aes))) implies that the kernel crypto API generates +the IV. Different IV generators are available. + +.. class:: toc-title + + Table of contents + +.. toctree:: + :maxdepth: 2 + + api-skcipher + api-aead + api-digest + api-rng + api-akcipher + api-kpp diff --git a/Documentation/crypto/architecture.rst b/Documentation/crypto/architecture.rst new file mode 100644 index 0000000..ca2d09b --- /dev/null +++ b/Documentation/crypto/architecture.rst @@ -0,0 +1,441 @@ +Kernel Crypto API Architecture +============================== + +Cipher algorithm types +---------------------- + +The kernel crypto API provides different API calls for the following +cipher types: + +- Symmetric ciphers + +- AEAD ciphers + +- Message digest, including keyed message digest + +- Random number generation + +- User space interface + +Ciphers And Templates +--------------------- + +The kernel crypto API provides implementations of single block ciphers +and message digests. In addition, the kernel crypto API provides +numerous "templates" that can be used in conjunction with the single +block ciphers and message digests. Templates include all types of block +chaining mode, the HMAC mechanism, etc. + +Single block ciphers and message digests can either be directly used by +a caller or invoked together with a template to form multi-block ciphers +or keyed message digests. + +A single block cipher may even be called with multiple templates. +However, templates cannot be used without a single cipher. + +See /proc/crypto and search for "name". For example: + +- aes + +- ecb(aes) + +- cmac(aes) + +- ccm(aes) + +- rfc4106(gcm(aes)) + +- sha1 + +- hmac(sha1) + +- authenc(hmac(sha1),cbc(aes)) + +In these examples, "aes" and "sha1" are the ciphers and all others are +the templates. + +Synchronous And Asynchronous Operation +-------------------------------------- + +The kernel crypto API provides synchronous and asynchronous API +operations. + +When using the synchronous API operation, the caller invokes a cipher +operation which is performed synchronously by the kernel crypto API. +That means, the caller waits until the cipher operation completes. +Therefore, the kernel crypto API calls work like regular function calls. +For synchronous operation, the set of API calls is small and +conceptually similar to any other crypto library. + +Asynchronous operation is provided by the kernel crypto API which +implies that the invocation of a cipher operation will complete almost +instantly. That invocation triggers the cipher operation but it does not +signal its completion. Before invoking a cipher operation, the caller +must provide a callback function the kernel crypto API can invoke to +signal the completion of the cipher operation. Furthermore, the caller +must ensure it can handle such asynchronous events by applying +appropriate locking around its data. The kernel crypto API does not +perform any special serialization operation to protect the caller's data +integrity. + +Crypto API Cipher References And Priority +----------------------------------------- + +A cipher is referenced by the caller with a string. That string has the +following semantics: + +:: + + template(single block cipher) + + +where "template" and "single block cipher" is the aforementioned +template and single block cipher, respectively. If applicable, +additional templates may enclose other templates, such as + +:: + + template1(template2(single block cipher))) + + +The kernel crypto API may provide multiple implementations of a template +or a single block cipher. For example, AES on newer Intel hardware has +the following implementations: AES-NI, assembler implementation, or +straight C. Now, when using the string "aes" with the kernel crypto API, +which cipher implementation is used? The answer to that question is the +priority number assigned to each cipher implementation by the kernel +crypto API. When a caller uses the string to refer to a cipher during +initialization of a cipher handle, the kernel crypto API looks up all +implementations providing an implementation with that name and selects +the implementation with the highest priority. + +Now, a caller may have the need to refer to a specific cipher +implementation and thus does not want to rely on the priority-based +selection. To accommodate this scenario, the kernel crypto API allows +the cipher implementation to register a unique name in addition to +common names. When using that unique name, a caller is therefore always +sure to refer to the intended cipher implementation. + +The list of available ciphers is given in /proc/crypto. However, that +list does not specify all possible permutations of templates and +ciphers. Each block listed in /proc/crypto may contain the following +information -- if one of the components listed as follows are not +applicable to a cipher, it is not displayed: + +- name: the generic name of the cipher that is subject to the + priority-based selection -- this name can be used by the cipher + allocation API calls (all names listed above are examples for such + generic names) + +- driver: the unique name of the cipher -- this name can be used by the + cipher allocation API calls + +- module: the kernel module providing the cipher implementation (or + "kernel" for statically linked ciphers) + +- priority: the priority value of the cipher implementation + +- refcnt: the reference count of the respective cipher (i.e. the number + of current consumers of this cipher) + +- selftest: specification whether the self test for the cipher passed + +- type: + + - skcipher for symmetric key ciphers + + - cipher for single block ciphers that may be used with an + additional template + + - shash for synchronous message digest + + - ahash for asynchronous message digest + + - aead for AEAD cipher type + + - compression for compression type transformations + + - rng for random number generator + + - givcipher for cipher with associated IV generator (see the geniv + entry below for the specification of the IV generator type used by + the cipher implementation) + + - kpp for a Key-agreement Protocol Primitive (KPP) cipher such as + an ECDH or DH implementation + +- blocksize: blocksize of cipher in bytes + +- keysize: key size in bytes + +- ivsize: IV size in bytes + +- seedsize: required size of seed data for random number generator + +- digestsize: output size of the message digest + +- geniv: IV generation type: + + - eseqiv for encrypted sequence number based IV generation + + - seqiv for sequence number based IV generation + + - chainiv for chain iv generation + + - <builtin> is a marker that the cipher implements IV generation and + handling as it is specific to the given cipher + +Key Sizes +--------- + +When allocating a cipher handle, the caller only specifies the cipher +type. Symmetric ciphers, however, typically support multiple key sizes +(e.g. AES-128 vs. AES-192 vs. AES-256). These key sizes are determined +with the length of the provided key. Thus, the kernel crypto API does +not provide a separate way to select the particular symmetric cipher key +size. + +Cipher Allocation Type And Masks +-------------------------------- + +The different cipher handle allocation functions allow the specification +of a type and mask flag. Both parameters have the following meaning (and +are therefore not covered in the subsequent sections). + +The type flag specifies the type of the cipher algorithm. The caller +usually provides a 0 when the caller wants the default handling. +Otherwise, the caller may provide the following selections which match +the aforementioned cipher types: + +- CRYPTO_ALG_TYPE_CIPHER Single block cipher + +- CRYPTO_ALG_TYPE_COMPRESS Compression + +- CRYPTO_ALG_TYPE_AEAD Authenticated Encryption with Associated Data + (MAC) + +- CRYPTO_ALG_TYPE_BLKCIPHER Synchronous multi-block cipher + +- CRYPTO_ALG_TYPE_ABLKCIPHER Asynchronous multi-block cipher + +- CRYPTO_ALG_TYPE_GIVCIPHER Asynchronous multi-block cipher packed + together with an IV generator (see geniv field in the /proc/crypto + listing for the known IV generators) + +- CRYPTO_ALG_TYPE_KPP Key-agreement Protocol Primitive (KPP) such as + an ECDH or DH implementation + +- CRYPTO_ALG_TYPE_DIGEST Raw message digest + +- CRYPTO_ALG_TYPE_HASH Alias for CRYPTO_ALG_TYPE_DIGEST + +- CRYPTO_ALG_TYPE_SHASH Synchronous multi-block hash + +- CRYPTO_ALG_TYPE_AHASH Asynchronous multi-block hash + +- CRYPTO_ALG_TYPE_RNG Random Number Generation + +- CRYPTO_ALG_TYPE_AKCIPHER Asymmetric cipher + +- CRYPTO_ALG_TYPE_PCOMPRESS Enhanced version of + CRYPTO_ALG_TYPE_COMPRESS allowing for segmented compression / + decompression instead of performing the operation on one segment + only. CRYPTO_ALG_TYPE_PCOMPRESS is intended to replace + CRYPTO_ALG_TYPE_COMPRESS once existing consumers are converted. + +The mask flag restricts the type of cipher. The only allowed flag is +CRYPTO_ALG_ASYNC to restrict the cipher lookup function to +asynchronous ciphers. Usually, a caller provides a 0 for the mask flag. + +When the caller provides a mask and type specification, the caller +limits the search the kernel crypto API can perform for a suitable +cipher implementation for the given cipher name. That means, even when a +caller uses a cipher name that exists during its initialization call, +the kernel crypto API may not select it due to the used type and mask +field. + +Internal Structure of Kernel Crypto API +--------------------------------------- + +The kernel crypto API has an internal structure where a cipher +implementation may use many layers and indirections. This section shall +help to clarify how the kernel crypto API uses various components to +implement the complete cipher. + +The following subsections explain the internal structure based on +existing cipher implementations. The first section addresses the most +complex scenario where all other scenarios form a logical subset. + +Generic AEAD Cipher Structure +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +The following ASCII art decomposes the kernel crypto API layers when +using the AEAD cipher with the automated IV generation. The shown +example is used by the IPSEC layer. + +For other use cases of AEAD ciphers, the ASCII art applies as well, but +the caller may not use the AEAD cipher with a separate IV generator. In +this case, the caller must generate the IV. + +The depicted example decomposes the AEAD cipher of GCM(AES) based on the +generic C implementations (gcm.c, aes-generic.c, ctr.c, ghash-generic.c, +seqiv.c). The generic implementation serves as an example showing the +complete logic of the kernel crypto API. + +It is possible that some streamlined cipher implementations (like +AES-NI) provide implementations merging aspects which in the view of the +kernel crypto API cannot be decomposed into layers any more. In case of +the AES-NI implementation, the CTR mode, the GHASH implementation and +the AES cipher are all merged into one cipher implementation registered +with the kernel crypto API. In this case, the concept described by the +following ASCII art applies too. However, the decomposition of GCM into +the individual sub-components by the kernel crypto API is not done any +more. + +Each block in the following ASCII art is an independent cipher instance +obtained from the kernel crypto API. Each block is accessed by the +caller or by other blocks using the API functions defined by the kernel +crypto API for the cipher implementation type. + +The blocks below indicate the cipher type as well as the specific logic +implemented in the cipher. + +The ASCII art picture also indicates the call structure, i.e. who calls +which component. The arrows point to the invoked block where the caller +uses the API applicable to the cipher type specified for the block. + +:: + + + kernel crypto API | IPSEC Layer + | + +-----------+ | + | | (1) + | aead | <----------------------------------- esp_output + | (seqiv) | ---+ + +-----------+ | + | (2) + +-----------+ | + | | <--+ (2) + | aead | <----------------------------------- esp_input + | (gcm) | ------------+ + +-----------+ | + | (3) | (5) + v v + +-----------+ +-----------+ + | | | | + | skcipher | | ahash | + | (ctr) | ---+ | (ghash) | + +-----------+ | +-----------+ + | + +-----------+ | (4) + | | <--+ + | cipher | + | (aes) | + +-----------+ + + + +The following call sequence is applicable when the IPSEC layer triggers +an encryption operation with the esp_output function. During +configuration, the administrator set up the use of rfc4106(gcm(aes)) as +the cipher for ESP. The following call sequence is now depicted in the +ASCII art above: + +1. esp_output() invokes crypto_aead_encrypt() to trigger an + encryption operation of the AEAD cipher with IV generator. + + In case of GCM, the SEQIV implementation is registered as GIVCIPHER + in crypto_rfc4106_alloc(). + + The SEQIV performs its operation to generate an IV where the core + function is seqiv_geniv(). + +2. Now, SEQIV uses the AEAD API function calls to invoke the associated + AEAD cipher. In our case, during the instantiation of SEQIV, the + cipher handle for GCM is provided to SEQIV. This means that SEQIV + invokes AEAD cipher operations with the GCM cipher handle. + + During instantiation of the GCM handle, the CTR(AES) and GHASH + ciphers are instantiated. The cipher handles for CTR(AES) and GHASH + are retained for later use. + + The GCM implementation is responsible to invoke the CTR mode AES and + the GHASH cipher in the right manner to implement the GCM + specification. + +3. The GCM AEAD cipher type implementation now invokes the SKCIPHER API + with the instantiated CTR(AES) cipher handle. + + During instantiation of the CTR(AES) cipher, the CIPHER type + implementation of AES is instantiated. The cipher handle for AES is + retained. + + That means that the SKCIPHER implementation of CTR(AES) only + implements the CTR block chaining mode. After performing the block + chaining operation, the CIPHER implementation of AES is invoked. + +4. The SKCIPHER of CTR(AES) now invokes the CIPHER API with the AES + cipher handle to encrypt one block. + +5. The GCM AEAD implementation also invokes the GHASH cipher + implementation via the AHASH API. + +When the IPSEC layer triggers the esp_input() function, the same call +sequence is followed with the only difference that the operation starts +with step (2). + +Generic Block Cipher Structure +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +Generic block ciphers follow the same concept as depicted with the ASCII +art picture above. + +For example, CBC(AES) is implemented with cbc.c, and aes-generic.c. The +ASCII art picture above applies as well with the difference that only +step (4) is used and the SKCIPHER block chaining mode is CBC. + +Generic Keyed Message Digest Structure +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +Keyed message digest implementations again follow the same concept as +depicted in the ASCII art picture above. + +For example, HMAC(SHA256) is implemented with hmac.c and +sha256_generic.c. The following ASCII art illustrates the +implementation: + +:: + + + kernel crypto API | Caller + | + +-----------+ (1) | + | | <------------------ some_function + | ahash | + | (hmac) | ---+ + +-----------+ | + | (2) + +-----------+ | + | | <--+ + | shash | + | (sha256) | + +-----------+ + + + +The following call sequence is applicable when a caller triggers an HMAC +operation: + +1. The AHASH API functions are invoked by the caller. The HMAC + implementation performs its operation as needed. + + During initialization of the HMAC cipher, the SHASH cipher type of + SHA256 is instantiated. The cipher handle for the SHA256 instance is + retained. + + At one time, the HMAC implementation requires a SHA256 operation + where the SHA256 cipher handle is used. + +2. The HMAC instance now invokes the SHASH API with the SHA256 cipher + handle to calculate the message digest. diff --git a/Documentation/crypto/devel-algos.rst b/Documentation/crypto/devel-algos.rst new file mode 100644 index 0000000..66f50d3 --- /dev/null +++ b/Documentation/crypto/devel-algos.rst @@ -0,0 +1,247 @@ +Developing Cipher Algorithms +============================ + +Registering And Unregistering Transformation +-------------------------------------------- + +There are three distinct types of registration functions in the Crypto +API. One is used to register a generic cryptographic transformation, +while the other two are specific to HASH transformations and +COMPRESSion. We will discuss the latter two in a separate chapter, here +we will only look at the generic ones. + +Before discussing the register functions, the data structure to be +filled with each, struct crypto_alg, must be considered -- see below +for a description of this data structure. + +The generic registration functions can be found in +include/linux/crypto.h and their definition can be seen below. The +former function registers a single transformation, while the latter +works on an array of transformation descriptions. The latter is useful +when registering transformations in bulk, for example when a driver +implements multiple transformations. + +:: + + int crypto_register_alg(struct crypto_alg *alg); + int crypto_register_algs(struct crypto_alg *algs, int count); + + +The counterparts to those functions are listed below. + +:: + + int crypto_unregister_alg(struct crypto_alg *alg); + int crypto_unregister_algs(struct crypto_alg *algs, int count); + + +Notice that both registration and unregistration functions do return a +value, so make sure to handle errors. A return code of zero implies +success. Any return code < 0 implies an error. + +The bulk registration/unregistration functions register/unregister each +transformation in the given array of length count. They handle errors as +follows: + +- crypto_register_algs() succeeds if and only if it successfully + registers all the given transformations. If an error occurs partway + through, then it rolls back successful registrations before returning + the error code. Note that if a driver needs to handle registration + errors for individual transformations, then it will need to use the + non-bulk function crypto_register_alg() instead. + +- crypto_unregister_algs() tries to unregister all the given + transformations, continuing on error. It logs errors and always + returns zero. + +Single-Block Symmetric Ciphers [CIPHER] +--------------------------------------- + +Example of transformations: aes, arc4, ... + +This section describes the simplest of all transformation +implementations, that being the CIPHER type used for symmetric ciphers. +The CIPHER type is used for transformations which operate on exactly one +block at a time and there are no dependencies between blocks at all. + +Registration specifics +~~~~~~~~~~~~~~~~~~~~~~ + +The registration of [CIPHER] algorithm is specific in that struct +crypto_alg field .cra_type is empty. The .cra_u.cipher has to be +filled in with proper callbacks to implement this transformation. + +See struct cipher_alg below. + +Cipher Definition With struct cipher_alg +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +Struct cipher_alg defines a single block cipher. + +Here are schematics of how these functions are called when operated from +other part of the kernel. Note that the .cia_setkey() call might happen +before or after any of these schematics happen, but must not happen +during any of these are in-flight. + +:: + + KEY ---. PLAINTEXT ---. + v v + .cia_setkey() -> .cia_encrypt() + | + '-----> CIPHERTEXT + + +Please note that a pattern where .cia_setkey() is called multiple times +is also valid: + +:: + + + KEY1 --. PLAINTEXT1 --. KEY2 --. PLAINTEXT2 --. + v v v v + .cia_setkey() -> .cia_encrypt() -> .cia_setkey() -> .cia_encrypt() + | | + '---> CIPHERTEXT1 '---> CIPHERTEXT2 + + +Multi-Block Ciphers +------------------- + +Example of transformations: cbc(aes), ecb(arc4), ... + +This section describes the multi-block cipher transformation +implementations. The multi-block ciphers are used for transformations +which operate on scatterlists of data supplied to the transformation +functions. They output the result into a scatterlist of data as well. + +Registration Specifics +~~~~~~~~~~~~~~~~~~~~~~ + +The registration of multi-block cipher algorithms is one of the most +standard procedures throughout the crypto API. + +Note, if a cipher implementation requires a proper alignment of data, +the caller should use the functions of crypto_skcipher_alignmask() to +identify a memory alignment mask. The kernel crypto API is able to +process requests that are unaligned. This implies, however, additional +overhead as the kernel crypto API needs to perform the realignment of +the data which may imply moving of data. + +Cipher Definition With struct blkcipher_alg and ablkcipher_alg +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +Struct blkcipher_alg defines a synchronous block cipher whereas struct +ablkcipher_alg defines an asynchronous block cipher. + +Please refer to the single block cipher description for schematics of +the block cipher usage. + +Specifics Of Asynchronous Multi-Block Cipher +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +There are a couple of specifics to the asynchronous interface. + +First of all, some of the drivers will want to use the Generic +ScatterWalk in case the hardware needs to be fed separate chunks of the +scatterlist which contains the plaintext and will contain the +ciphertext. Please refer to the ScatterWalk interface offered by the +Linux kernel scatter / gather list implementation. + +Hashing [HASH] +-------------- + +Example of transformations: crc32, md5, sha1, sha256,... + +Registering And Unregistering The Transformation +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +There are multiple ways to register a HASH transformation, depending on +whether the transformation is synchronous [SHASH] or asynchronous +[AHASH] and the amount of HASH transformations we are registering. You +can find the prototypes defined in include/crypto/internal/hash.h: + +:: + + int crypto_register_ahash(struct ahash_alg *alg); + + int crypto_register_shash(struct shash_alg *alg); + int crypto_register_shashes(struct shash_alg *algs, int count); + + +The respective counterparts for unregistering the HASH transformation +are as follows: + +:: + + int crypto_unregister_ahash(struct ahash_alg *alg); + + int crypto_unregister_shash(struct shash_alg *alg); + int crypto_unregister_shashes(struct shash_alg *algs, int count); + + +Cipher Definition With struct shash_alg and ahash_alg +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +Here are schematics of how these functions are called when operated from +other part of the kernel. Note that the .setkey() call might happen +before or after any of these schematics happen, but must not happen +during any of these are in-flight. Please note that calling .init() +followed immediately by .finish() is also a perfectly valid +transformation. + +:: + + I) DATA -----------. + v + .init() -> .update() -> .final() ! .update() might not be called + ^ | | at all in this scenario. + '----' '---> HASH + + II) DATA -----------.-----------. + v v + .init() -> .update() -> .finup() ! .update() may not be called + ^ | | at all in this scenario. + '----' '---> HASH + + III) DATA -----------. + v + .digest() ! The entire process is handled + | by the .digest() call. + '---------------> HASH + + +Here is a schematic of how the .export()/.import() functions are called +when used from another part of the kernel. + +:: + + KEY--. DATA--. + v v ! .update() may not be called + .setkey() -> .init() -> .update() -> .export() at all in this scenario. + ^ | | + '-----' '--> PARTIAL_HASH + + ----------- other transformations happen here ----------- + + PARTIAL_HASH--. DATA1--. + v v + .import -> .update() -> .final() ! .update() may not be called + ^ | | at all in this scenario. + '----' '--> HASH1 + + PARTIAL_HASH--. DATA2-. + v v + .import -> .finup() + | + '---------------> HASH2 + + +Specifics Of Asynchronous HASH Transformation +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +Some of the drivers will want to use the Generic ScatterWalk in case the +implementation needs to be fed separate chunks of the scatterlist which +contains the input data. The buffer containing the resulting hash will +always be properly aligned to .cra_alignmask so there is no need to +worry about this. diff --git a/Documentation/crypto/index.rst b/Documentation/crypto/index.rst new file mode 100644 index 0000000..94c4786 --- /dev/null +++ b/Documentation/crypto/index.rst @@ -0,0 +1,24 @@ +======================= +Linux Kernel Crypto API +======================= + +:Author: Stephan Mueller +:Author: Marek Vasut + +This documentation outlines the Linux kernel crypto API with its +concepts, details about developing cipher implementations, employment of the API +for cryptographic use cases, as well as programming examples. + +.. class:: toc-title + + Table of contents + +.. toctree:: + :maxdepth: 2 + + intro + architecture + devel-algos + userspace-if + api + api-samples diff --git a/Documentation/crypto/intro.rst b/Documentation/crypto/intro.rst new file mode 100644 index 0000000..9aa89eb --- /dev/null +++ b/Documentation/crypto/intro.rst @@ -0,0 +1,74 @@ +Kernel Crypto API Interface Specification +========================================= + +Introduction +------------ + +The kernel crypto API offers a rich set of cryptographic ciphers as well +as other data transformation mechanisms and methods to invoke these. +This document contains a description of the API and provides example +code. + +To understand and properly use the kernel crypto API a brief explanation +of its structure is given. Based on the architecture, the API can be +separated into different components. Following the architecture +specification, hints to developers of ciphers are provided. Pointers to +the API function call documentation are given at the end. + +The kernel crypto API refers to all algorithms as "transformations". +Therefore, a cipher handle variable usually has the name "tfm". Besides +cryptographic operations, the kernel crypto API also knows compression +transformations and handles them the same way as ciphers. + +The kernel crypto API serves the following entity types: + +- consumers requesting cryptographic services + +- data transformation implementations (typically ciphers) that can be + called by consumers using the kernel crypto API + +This specification is intended for consumers of the kernel crypto API as +well as for developers implementing ciphers. This API specification, +however, does not discuss all API calls available to data transformation +implementations (i.e. implementations of ciphers and other +transformations (such as CRC or even compression algorithms) that can +register with the kernel crypto API). + +Note: The terms "transformation" and cipher algorithm are used +interchangeably. + +Terminology +----------- + +The transformation implementation is an actual code or interface to +hardware which implements a certain transformation with precisely +defined behavior. + +The transformation object (TFM) is an instance of a transformation +implementation. There can be multiple transformation objects associated +with a single transformation implementation. Each of those +transformation objects is held by a crypto API consumer or another +transformation. Transformation object is allocated when a crypto API +consumer requests a transformation implementation. The consumer is then +provided with a structure, which contains a transformation object (TFM). + +The structure that contains transformation objects may also be referred +to as a "cipher handle". Such a cipher handle is always subject to the +following phases that are reflected in the API calls applicable to such +a cipher handle: + +1. Initialization of a cipher handle. + +2. Execution of all intended cipher operations applicable for the handle + where the cipher handle must be furnished to every API call. + +3. Destruction of a cipher handle. + +When using the initialization API calls, a cipher handle is created and +returned to the consumer. Therefore, please refer to all initialization +API calls that refer to the data structure type a consumer is expected +to receive and subsequently to use. The initialization API calls have +all the same naming conventions of crypto_alloc\*. + +The transformation context is private data associated with the +transformation object. diff --git a/Documentation/crypto/userspace-if.rst b/Documentation/crypto/userspace-if.rst new file mode 100644 index 0000000..de5a72e --- /dev/null +++ b/Documentation/crypto/userspace-if.rst @@ -0,0 +1,387 @@ +User Space Interface +==================== + +Introduction +------------ + +The concepts of the kernel crypto API visible to kernel space is fully +applicable to the user space interface as well. Therefore, the kernel +crypto API high level discussion for the in-kernel use cases applies +here as well. + +The major difference, however, is that user space can only act as a +consumer and never as a provider of a transformation or cipher +algorithm. + +The following covers the user space interface exported by the kernel +crypto API. A working example of this description is libkcapi that can +be obtained from [1]. That library can be used by user space +applications that require cryptographic services from the kernel. + +Some details of the in-kernel kernel crypto API aspects do not apply to +user space, however. This includes the difference between synchronous +and asynchronous invocations. The user space API call is fully +synchronous. + +[1] http://www.chronox.de/libkcapi.html + +User Space API General Remarks +------------------------------ + +The kernel crypto API is accessible from user space. Currently, the +following ciphers are accessible: + +- Message digest including keyed message digest (HMAC, CMAC) + +- Symmetric ciphers + +- AEAD ciphers + +- Random Number Generators + +The interface is provided via socket type using the type AF_ALG. In +addition, the setsockopt option type is SOL_ALG. In case the user space +header files do not export these flags yet, use the following macros: + +:: + + #ifndef AF_ALG + #define AF_ALG 38 + #endif + #ifndef SOL_ALG + #define SOL_ALG 279 + #endif + + +A cipher is accessed with the same name as done for the in-kernel API +calls. This includes the generic vs. unique naming schema for ciphers as +well as the enforcement of priorities for generic names. + +To interact with the kernel crypto API, a socket must be created by the +user space application. User space invokes the cipher operation with the +send()/write() system call family. The result of the cipher operation is +obtained with the read()/recv() system call family. + +The following API calls assume that the socket descriptor is already +opened by the user space application and discusses only the kernel +crypto API specific invocations. + +To initialize the socket interface, the following sequence has to be +performed by the consumer: + +1. Create a socket of type AF_ALG with the struct sockaddr_alg + parameter specified below for the different cipher types. + +2. Invoke bind with the socket descriptor + +3. Invoke accept with the socket descriptor. The accept system call + returns a new file descriptor that is to be used to interact with the + particular cipher instance. When invoking send/write or recv/read + system calls to send data to the kernel or obtain data from the + kernel, the file descriptor returned by accept must be used. + +In-place Cipher operation +------------------------- + +Just like the in-kernel operation of the kernel crypto API, the user +space interface allows the cipher operation in-place. That means that +the input buffer used for the send/write system call and the output +buffer used by the read/recv system call may be one and the same. This +is of particular interest for symmetric cipher operations where a +copying of the output data to its final destination can be avoided. + +If a consumer on the other hand wants to maintain the plaintext and the +ciphertext in different memory locations, all a consumer needs to do is +to provide different memory pointers for the encryption and decryption +operation. + +Message Digest API +------------------ + +The message digest type to be used for the cipher operation is selected +when invoking the bind syscall. bind requires the caller to provide a +filled struct sockaddr data structure. This data structure must be +filled as follows: + +:: + + struct sockaddr_alg sa = { + .salg_family = AF_ALG, + .salg_type = "hash", /* this selects the hash logic in the kernel */ + .salg_name = "sha1" /* this is the cipher name */ + }; + + +The salg_type value "hash" applies to message digests and keyed message +digests. Though, a keyed message digest is referenced by the appropriate +salg_name. Please see below for the setsockopt interface that explains +how the key can be set for a keyed message digest. + +Using the send() system call, the application provides the data that +should be processed with the message digest. The send system call allows +the following flags to be specified: + +- MSG_MORE: If this flag is set, the send system call acts like a + message digest update function where the final hash is not yet + calculated. If the flag is not set, the send system call calculates + the final message digest immediately. + +With the recv() system call, the application can read the message digest +from the kernel crypto API. If the buffer is too small for the message +digest, the flag MSG_TRUNC is set by the kernel. + +In order to set a message digest key, the calling application must use +the setsockopt() option of ALG_SET_KEY. If the key is not set the HMAC +operation is performed without the initial HMAC state change caused by +the key. + +Symmetric Cipher API +-------------------- + +The operation is very similar to the message digest discussion. During +initialization, the struct sockaddr data structure must be filled as +follows: + +:: + + struct sockaddr_alg sa = { + .salg_family = AF_ALG, + .salg_type = "skcipher", /* this selects the symmetric cipher */ + .salg_name = "cbc(aes)" /* this is the cipher name */ + }; + + +Before data can be sent to the kernel using the write/send system call +family, the consumer must set the key. The key setting is described with +the setsockopt invocation below. + +Using the sendmsg() system call, the application provides the data that +should be processed for encryption or decryption. In addition, the IV is +specified with the data structure provided by the sendmsg() system call. + +The sendmsg system call parameter of struct msghdr is embedded into the +struct cmsghdr data structure. See recv(2) and cmsg(3) for more +information on how the cmsghdr data structure is used together with the +send/recv system call family. That cmsghdr data structure holds the +following information specified with a separate header instances: + +- specification of the cipher operation type with one of these flags: + + - ALG_OP_ENCRYPT - encryption of data + + - ALG_OP_DECRYPT - decryption of data + +- specification of the IV information marked with the flag ALG_SET_IV + +The send system call family allows the following flag to be specified: + +- MSG_MORE: If this flag is set, the send system call acts like a + cipher update function where more input data is expected with a + subsequent invocation of the send system call. + +Note: The kernel reports -EINVAL for any unexpected data. The caller +must make sure that all data matches the constraints given in +/proc/crypto for the selected cipher. + +With the recv() system call, the application can read the result of the +cipher operation from the kernel crypto API. The output buffer must be +at least as large as to hold all blocks of the encrypted or decrypted +data. If the output data size is smaller, only as many blocks are +returned that fit into that output buffer size. + +AEAD Cipher API +--------------- + +The operation is very similar to the symmetric cipher discussion. During +initialization, the struct sockaddr data structure must be filled as +follows: + +:: + + struct sockaddr_alg sa = { + .salg_family = AF_ALG, + .salg_type = "aead", /* this selects the symmetric cipher */ + .salg_name = "gcm(aes)" /* this is the cipher name */ + }; + + +Before data can be sent to the kernel using the write/send system call +family, the consumer must set the key. The key setting is described with +the setsockopt invocation below. + +In addition, before data can be sent to the kernel using the write/send +system call family, the consumer must set the authentication tag size. +To set the authentication tag size, the caller must use the setsockopt +invocation described below. + +Using the sendmsg() system call, the application provides the data that +should be processed for encryption or decryption. In addition, the IV is +specified with the data structure provided by the sendmsg() system call. + +The sendmsg system call parameter of struct msghdr is embedded into the +struct cmsghdr data structure. See recv(2) and cmsg(3) for more +information on how the cmsghdr data structure is used together with the +send/recv system call family. That cmsghdr data structure holds the +following information specified with a separate header instances: + +- specification of the cipher operation type with one of these flags: + + - ALG_OP_ENCRYPT - encryption of data + + - ALG_OP_DECRYPT - decryption of data + +- specification of the IV information marked with the flag ALG_SET_IV + +- specification of the associated authentication data (AAD) with the + flag ALG_SET_AEAD_ASSOCLEN. The AAD is sent to the kernel together + with the plaintext / ciphertext. See below for the memory structure. + +The send system call family allows the following flag to be specified: + +- MSG_MORE: If this flag is set, the send system call acts like a + cipher update function where more input data is expected with a + subsequent invocation of the send system call. + +Note: The kernel reports -EINVAL for any unexpected data. The caller +must make sure that all data matches the constraints given in +/proc/crypto for the selected cipher. + +With the recv() system call, the application can read the result of the +cipher operation from the kernel crypto API. The output buffer must be +at least as large as defined with the memory structure below. If the +output data size is smaller, the cipher operation is not performed. + +The authenticated decryption operation may indicate an integrity error. +Such breach in integrity is marked with the -EBADMSG error code. + +AEAD Memory Structure +~~~~~~~~~~~~~~~~~~~~~ + +The AEAD cipher operates with the following information that is +communicated between user and kernel space as one data stream: + +- plaintext or ciphertext + +- associated authentication data (AAD) + +- authentication tag + +The sizes of the AAD and the authentication tag are provided with the +sendmsg and setsockopt calls (see there). As the kernel knows the size +of the entire data stream, the kernel is now able to calculate the right +offsets of the data components in the data stream. + +The user space caller must arrange the aforementioned information in the +following order: + +- AEAD encryption input: AAD \|\| plaintext + +- AEAD decryption input: AAD \|\| ciphertext \|\| authentication tag + +The output buffer the user space caller provides must be at least as +large to hold the following data: + +- AEAD encryption output: ciphertext \|\| authentication tag + +- AEAD decryption output: plaintext + +Random Number Generator API +--------------------------- + +Again, the operation is very similar to the other APIs. During +initialization, the struct sockaddr data structure must be filled as +follows: + +:: + + struct sockaddr_alg sa = { + .salg_family = AF_ALG, + .salg_type = "rng", /* this selects the symmetric cipher */ + .salg_name = "drbg_nopr_sha256" /* this is the cipher name */ + }; + + +Depending on the RNG type, the RNG must be seeded. The seed is provided +using the setsockopt interface to set the key. For example, the +ansi_cprng requires a seed. The DRBGs do not require a seed, but may be +seeded. + +Using the read()/recvmsg() system calls, random numbers can be obtained. +The kernel generates at most 128 bytes in one call. If user space +requires more data, multiple calls to read()/recvmsg() must be made. + +WARNING: The user space caller may invoke the initially mentioned accept +system call multiple times. In this case, the returned file descriptors +have the same state. + +Zero-Copy Interface +------------------- + +In addition to the send/write/read/recv system call family, the AF_ALG +interface can be accessed with the zero-copy interface of +splice/vmsplice. As the name indicates, the kernel tries to avoid a copy +operation into kernel space. + +The zero-copy operation requires data to be aligned at the page +boundary. Non-aligned data can be used as well, but may require more +operations of the kernel which would defeat the speed gains obtained +from the zero-copy interface. + +The system-interent limit for the size of one zero-copy operation is 16 +pages. If more data is to be sent to AF_ALG, user space must slice the +input into segments with a maximum size of 16 pages. + +Zero-copy can be used with the following code example (a complete +working example is provided with libkcapi): + +:: + + int pipes[2]; + + pipe(pipes); + /* input data in iov */ + vmsplice(pipes[1], iov, iovlen, SPLICE_F_GIFT); + /* opfd is the file descriptor returned from accept() system call */ + splice(pipes[0], NULL, opfd, NULL, ret, 0); + read(opfd, out, outlen); + + +Setsockopt Interface +-------------------- + +In addition to the read/recv and send/write system call handling to send +and retrieve data subject to the cipher operation, a consumer also needs +to set the additional information for the cipher operation. This +additional information is set using the setsockopt system call that must +be invoked with the file descriptor of the open cipher (i.e. the file +descriptor returned by the accept system call). + +Each setsockopt invocation must use the level SOL_ALG. + +The setsockopt interface allows setting the following data using the +mentioned optname: + +- ALG_SET_KEY -- Setting the key. Key setting is applicable to: + + - the skcipher cipher type (symmetric ciphers) + + - the hash cipher type (keyed message digests) + + - the AEAD cipher type + + - the RNG cipher type to provide the seed + +- ALG_SET_AEAD_AUTHSIZE -- Setting the authentication tag size for + AEAD ciphers. For a encryption operation, the authentication tag of + the given size will be generated. For a decryption operation, the + provided ciphertext is assumed to contain an authentication tag of + the given size (see section about AEAD memory layout below). + +User space API example +---------------------- + +Please see [1] for libkcapi which provides an easy-to-use wrapper around +the aforementioned Netlink kernel interface. [1] also contains a test +application that invokes all libkcapi API calls. + +[1] http://www.chronox.de/libkcapi.html |
