1 User Space Interface 1 User Space Interface
2 ==================== 2 ====================
3 3
4 Introduction 4 Introduction
5 ------------ 5 ------------
6 6
7 The concepts of the kernel crypto API visible 7 The concepts of the kernel crypto API visible to kernel space is fully
8 applicable to the user space interface as well 8 applicable to the user space interface as well. Therefore, the kernel
9 crypto API high level discussion for the in-ke 9 crypto API high level discussion for the in-kernel use cases applies
10 here as well. 10 here as well.
11 11
12 The major difference, however, is that user sp 12 The major difference, however, is that user space can only act as a
13 consumer and never as a provider of a transfor 13 consumer and never as a provider of a transformation or cipher
14 algorithm. 14 algorithm.
15 15
16 The following covers the user space interface 16 The following covers the user space interface exported by the kernel
17 crypto API. A working example of this descript 17 crypto API. A working example of this description is libkcapi that can
18 be obtained from [1]. That library can be used 18 be obtained from [1]. That library can be used by user space
19 applications that require cryptographic servic 19 applications that require cryptographic services from the kernel.
20 20
21 Some details of the in-kernel kernel crypto AP 21 Some details of the in-kernel kernel crypto API aspects do not apply to
22 user space, however. This includes the differe 22 user space, however. This includes the difference between synchronous
23 and asynchronous invocations. The user space A 23 and asynchronous invocations. The user space API call is fully
24 synchronous. 24 synchronous.
25 25
26 [1] https://www.chronox.de/libkcapi.html 26 [1] https://www.chronox.de/libkcapi.html
27 27
28 User Space API General Remarks 28 User Space API General Remarks
29 ------------------------------ 29 ------------------------------
30 30
31 The kernel crypto API is accessible from user 31 The kernel crypto API is accessible from user space. Currently, the
32 following ciphers are accessible: 32 following ciphers are accessible:
33 33
34 - Message digest including keyed message dige 34 - Message digest including keyed message digest (HMAC, CMAC)
35 35
36 - Symmetric ciphers 36 - Symmetric ciphers
37 37
38 - AEAD ciphers 38 - AEAD ciphers
39 39
40 - Random Number Generators 40 - Random Number Generators
41 41
42 The interface is provided via socket type usin 42 The interface is provided via socket type using the type AF_ALG. In
43 addition, the setsockopt option type is SOL_AL 43 addition, the setsockopt option type is SOL_ALG. In case the user space
44 header files do not export these flags yet, us 44 header files do not export these flags yet, use the following macros:
45 45
46 :: 46 ::
47 47
48 #ifndef AF_ALG 48 #ifndef AF_ALG
49 #define AF_ALG 38 49 #define AF_ALG 38
50 #endif 50 #endif
51 #ifndef SOL_ALG 51 #ifndef SOL_ALG
52 #define SOL_ALG 279 52 #define SOL_ALG 279
53 #endif 53 #endif
54 54
55 55
56 A cipher is accessed with the same name as don 56 A cipher is accessed with the same name as done for the in-kernel API
57 calls. This includes the generic vs. unique na 57 calls. This includes the generic vs. unique naming schema for ciphers as
58 well as the enforcement of priorities for gene 58 well as the enforcement of priorities for generic names.
59 59
60 To interact with the kernel crypto API, a sock 60 To interact with the kernel crypto API, a socket must be created by the
61 user space application. User space invokes the 61 user space application. User space invokes the cipher operation with the
62 send()/write() system call family. The result 62 send()/write() system call family. The result of the cipher operation is
63 obtained with the read()/recv() system call fa 63 obtained with the read()/recv() system call family.
64 64
65 The following API calls assume that the socket 65 The following API calls assume that the socket descriptor is already
66 opened by the user space application and discu 66 opened by the user space application and discusses only the kernel
67 crypto API specific invocations. 67 crypto API specific invocations.
68 68
69 To initialize the socket interface, the follow 69 To initialize the socket interface, the following sequence has to be
70 performed by the consumer: 70 performed by the consumer:
71 71
72 1. Create a socket of type AF_ALG with the str 72 1. Create a socket of type AF_ALG with the struct sockaddr_alg
73 parameter specified below for the different 73 parameter specified below for the different cipher types.
74 74
75 2. Invoke bind with the socket descriptor 75 2. Invoke bind with the socket descriptor
76 76
77 3. Invoke accept with the socket descriptor. T 77 3. Invoke accept with the socket descriptor. The accept system call
78 returns a new file descriptor that is to be 78 returns a new file descriptor that is to be used to interact with the
79 particular cipher instance. When invoking s 79 particular cipher instance. When invoking send/write or recv/read
80 system calls to send data to the kernel or 80 system calls to send data to the kernel or obtain data from the
81 kernel, the file descriptor returned by acc 81 kernel, the file descriptor returned by accept must be used.
82 82
83 In-place Cipher operation 83 In-place Cipher operation
84 ------------------------- 84 -------------------------
85 85
86 Just like the in-kernel operation of the kerne 86 Just like the in-kernel operation of the kernel crypto API, the user
87 space interface allows the cipher operation in 87 space interface allows the cipher operation in-place. That means that
88 the input buffer used for the send/write syste 88 the input buffer used for the send/write system call and the output
89 buffer used by the read/recv system call may b 89 buffer used by the read/recv system call may be one and the same. This
90 is of particular interest for symmetric cipher 90 is of particular interest for symmetric cipher operations where a
91 copying of the output data to its final destin 91 copying of the output data to its final destination can be avoided.
92 92
93 If a consumer on the other hand wants to maint 93 If a consumer on the other hand wants to maintain the plaintext and the
94 ciphertext in different memory locations, all 94 ciphertext in different memory locations, all a consumer needs to do is
95 to provide different memory pointers for the e 95 to provide different memory pointers for the encryption and decryption
96 operation. 96 operation.
97 97
98 Message Digest API 98 Message Digest API
99 ------------------ 99 ------------------
100 100
101 The message digest type to be used for the cip 101 The message digest type to be used for the cipher operation is selected
102 when invoking the bind syscall. bind requires 102 when invoking the bind syscall. bind requires the caller to provide a
103 filled struct sockaddr data structure. This da 103 filled struct sockaddr data structure. This data structure must be
104 filled as follows: 104 filled as follows:
105 105
106 :: 106 ::
107 107
108 struct sockaddr_alg sa = { 108 struct sockaddr_alg sa = {
109 .salg_family = AF_ALG, 109 .salg_family = AF_ALG,
110 .salg_type = "hash", /* this selects t 110 .salg_type = "hash", /* this selects the hash logic in the kernel */
111 .salg_name = "sha1" /* this is the cip 111 .salg_name = "sha1" /* this is the cipher name */
112 }; 112 };
113 113
114 114
115 The salg_type value "hash" applies to message 115 The salg_type value "hash" applies to message digests and keyed message
116 digests. Though, a keyed message digest is ref 116 digests. Though, a keyed message digest is referenced by the appropriate
117 salg_name. Please see below for the setsockopt 117 salg_name. Please see below for the setsockopt interface that explains
118 how the key can be set for a keyed message dig 118 how the key can be set for a keyed message digest.
119 119
120 Using the send() system call, the application 120 Using the send() system call, the application provides the data that
121 should be processed with the message digest. T 121 should be processed with the message digest. The send system call allows
122 the following flags to be specified: 122 the following flags to be specified:
123 123
124 - MSG_MORE: If this flag is set, the send sys 124 - MSG_MORE: If this flag is set, the send system call acts like a
125 message digest update function where the fi 125 message digest update function where the final hash is not yet
126 calculated. If the flag is not set, the sen 126 calculated. If the flag is not set, the send system call calculates
127 the final message digest immediately. 127 the final message digest immediately.
128 128
129 With the recv() system call, the application c 129 With the recv() system call, the application can read the message digest
130 from the kernel crypto API. If the buffer is t 130 from the kernel crypto API. If the buffer is too small for the message
131 digest, the flag MSG_TRUNC is set by the kerne 131 digest, the flag MSG_TRUNC is set by the kernel.
132 132
133 In order to set a message digest key, the call 133 In order to set a message digest key, the calling application must use
134 the setsockopt() option of ALG_SET_KEY or ALG_ 134 the setsockopt() option of ALG_SET_KEY or ALG_SET_KEY_BY_KEY_SERIAL. If the
135 key is not set the HMAC operation is performed 135 key is not set the HMAC operation is performed without the initial HMAC state
136 change caused by the key. 136 change caused by the key.
137 137
138 Symmetric Cipher API 138 Symmetric Cipher API
139 -------------------- 139 --------------------
140 140
141 The operation is very similar to the message d 141 The operation is very similar to the message digest discussion. During
142 initialization, the struct sockaddr data struc 142 initialization, the struct sockaddr data structure must be filled as
143 follows: 143 follows:
144 144
145 :: 145 ::
146 146
147 struct sockaddr_alg sa = { 147 struct sockaddr_alg sa = {
148 .salg_family = AF_ALG, 148 .salg_family = AF_ALG,
149 .salg_type = "skcipher", /* this selec 149 .salg_type = "skcipher", /* this selects the symmetric cipher */
150 .salg_name = "cbc(aes)" /* this is the 150 .salg_name = "cbc(aes)" /* this is the cipher name */
151 }; 151 };
152 152
153 153
154 Before data can be sent to the kernel using th 154 Before data can be sent to the kernel using the write/send system call
155 family, the consumer must set the key. The key 155 family, the consumer must set the key. The key setting is described with
156 the setsockopt invocation below. 156 the setsockopt invocation below.
157 157
158 Using the sendmsg() system call, the applicati 158 Using the sendmsg() system call, the application provides the data that
159 should be processed for encryption or decrypti 159 should be processed for encryption or decryption. In addition, the IV is
160 specified with the data structure provided by 160 specified with the data structure provided by the sendmsg() system call.
161 161
162 The sendmsg system call parameter of struct ms 162 The sendmsg system call parameter of struct msghdr is embedded into the
163 struct cmsghdr data structure. See recv(2) and 163 struct cmsghdr data structure. See recv(2) and cmsg(3) for more
164 information on how the cmsghdr data structure 164 information on how the cmsghdr data structure is used together with the
165 send/recv system call family. That cmsghdr dat 165 send/recv system call family. That cmsghdr data structure holds the
166 following information specified with a separat 166 following information specified with a separate header instances:
167 167
168 - specification of the cipher operation type 168 - specification of the cipher operation type with one of these flags:
169 169
170 - ALG_OP_ENCRYPT - encryption of data 170 - ALG_OP_ENCRYPT - encryption of data
171 171
172 - ALG_OP_DECRYPT - decryption of data 172 - ALG_OP_DECRYPT - decryption of data
173 173
174 - specification of the IV information marked 174 - specification of the IV information marked with the flag ALG_SET_IV
175 175
176 The send system call family allows the followi 176 The send system call family allows the following flag to be specified:
177 177
178 - MSG_MORE: If this flag is set, the send sys 178 - MSG_MORE: If this flag is set, the send system call acts like a
179 cipher update function where more input dat 179 cipher update function where more input data is expected with a
180 subsequent invocation of the send system ca 180 subsequent invocation of the send system call.
181 181
182 Note: The kernel reports -EINVAL for any unexp 182 Note: The kernel reports -EINVAL for any unexpected data. The caller
183 must make sure that all data matches the const 183 must make sure that all data matches the constraints given in
184 /proc/crypto for the selected cipher. 184 /proc/crypto for the selected cipher.
185 185
186 With the recv() system call, the application c 186 With the recv() system call, the application can read the result of the
187 cipher operation from the kernel crypto API. T 187 cipher operation from the kernel crypto API. The output buffer must be
188 at least as large as to hold all blocks of the 188 at least as large as to hold all blocks of the encrypted or decrypted
189 data. If the output data size is smaller, only 189 data. If the output data size is smaller, only as many blocks are
190 returned that fit into that output buffer size 190 returned that fit into that output buffer size.
191 191
192 AEAD Cipher API 192 AEAD Cipher API
193 --------------- 193 ---------------
194 194
195 The operation is very similar to the symmetric 195 The operation is very similar to the symmetric cipher discussion. During
196 initialization, the struct sockaddr data struc 196 initialization, the struct sockaddr data structure must be filled as
197 follows: 197 follows:
198 198
199 :: 199 ::
200 200
201 struct sockaddr_alg sa = { 201 struct sockaddr_alg sa = {
202 .salg_family = AF_ALG, 202 .salg_family = AF_ALG,
203 .salg_type = "aead", /* this selects t 203 .salg_type = "aead", /* this selects the symmetric cipher */
204 .salg_name = "gcm(aes)" /* this is the 204 .salg_name = "gcm(aes)" /* this is the cipher name */
205 }; 205 };
206 206
207 207
208 Before data can be sent to the kernel using th 208 Before data can be sent to the kernel using the write/send system call
209 family, the consumer must set the key. The key 209 family, the consumer must set the key. The key setting is described with
210 the setsockopt invocation below. 210 the setsockopt invocation below.
211 211
212 In addition, before data can be sent to the ke 212 In addition, before data can be sent to the kernel using the write/send
213 system call family, the consumer must set the 213 system call family, the consumer must set the authentication tag size.
214 To set the authentication tag size, the caller 214 To set the authentication tag size, the caller must use the setsockopt
215 invocation described below. 215 invocation described below.
216 216
217 Using the sendmsg() system call, the applicati 217 Using the sendmsg() system call, the application provides the data that
218 should be processed for encryption or decrypti 218 should be processed for encryption or decryption. In addition, the IV is
219 specified with the data structure provided by 219 specified with the data structure provided by the sendmsg() system call.
220 220
221 The sendmsg system call parameter of struct ms 221 The sendmsg system call parameter of struct msghdr is embedded into the
222 struct cmsghdr data structure. See recv(2) and 222 struct cmsghdr data structure. See recv(2) and cmsg(3) for more
223 information on how the cmsghdr data structure 223 information on how the cmsghdr data structure is used together with the
224 send/recv system call family. That cmsghdr dat 224 send/recv system call family. That cmsghdr data structure holds the
225 following information specified with a separat 225 following information specified with a separate header instances:
226 226
227 - specification of the cipher operation type 227 - specification of the cipher operation type with one of these flags:
228 228
229 - ALG_OP_ENCRYPT - encryption of data 229 - ALG_OP_ENCRYPT - encryption of data
230 230
231 - ALG_OP_DECRYPT - decryption of data 231 - ALG_OP_DECRYPT - decryption of data
232 232
233 - specification of the IV information marked 233 - specification of the IV information marked with the flag ALG_SET_IV
234 234
235 - specification of the associated authenticat 235 - specification of the associated authentication data (AAD) with the
236 flag ALG_SET_AEAD_ASSOCLEN. The AAD is sent 236 flag ALG_SET_AEAD_ASSOCLEN. The AAD is sent to the kernel together
237 with the plaintext / ciphertext. See below 237 with the plaintext / ciphertext. See below for the memory structure.
238 238
239 The send system call family allows the followi 239 The send system call family allows the following flag to be specified:
240 240
241 - MSG_MORE: If this flag is set, the send sys 241 - MSG_MORE: If this flag is set, the send system call acts like a
242 cipher update function where more input dat 242 cipher update function where more input data is expected with a
243 subsequent invocation of the send system ca 243 subsequent invocation of the send system call.
244 244
245 Note: The kernel reports -EINVAL for any unexp 245 Note: The kernel reports -EINVAL for any unexpected data. The caller
246 must make sure that all data matches the const 246 must make sure that all data matches the constraints given in
247 /proc/crypto for the selected cipher. 247 /proc/crypto for the selected cipher.
248 248
249 With the recv() system call, the application c 249 With the recv() system call, the application can read the result of the
250 cipher operation from the kernel crypto API. T 250 cipher operation from the kernel crypto API. The output buffer must be
251 at least as large as defined with the memory s 251 at least as large as defined with the memory structure below. If the
252 output data size is smaller, the cipher operat 252 output data size is smaller, the cipher operation is not performed.
253 253
254 The authenticated decryption operation may ind 254 The authenticated decryption operation may indicate an integrity error.
255 Such breach in integrity is marked with the -E 255 Such breach in integrity is marked with the -EBADMSG error code.
256 256
257 AEAD Memory Structure 257 AEAD Memory Structure
258 ~~~~~~~~~~~~~~~~~~~~~ 258 ~~~~~~~~~~~~~~~~~~~~~
259 259
260 The AEAD cipher operates with the following in 260 The AEAD cipher operates with the following information that is
261 communicated between user and kernel space as 261 communicated between user and kernel space as one data stream:
262 262
263 - plaintext or ciphertext 263 - plaintext or ciphertext
264 264
265 - associated authentication data (AAD) 265 - associated authentication data (AAD)
266 266
267 - authentication tag 267 - authentication tag
268 268
269 The sizes of the AAD and the authentication ta 269 The sizes of the AAD and the authentication tag are provided with the
270 sendmsg and setsockopt calls (see there). As t 270 sendmsg and setsockopt calls (see there). As the kernel knows the size
271 of the entire data stream, the kernel is now a 271 of the entire data stream, the kernel is now able to calculate the right
272 offsets of the data components in the data str 272 offsets of the data components in the data stream.
273 273
274 The user space caller must arrange the aforeme 274 The user space caller must arrange the aforementioned information in the
275 following order: 275 following order:
276 276
277 - AEAD encryption input: AAD \|\| plaintext 277 - AEAD encryption input: AAD \|\| plaintext
278 278
279 - AEAD decryption input: AAD \|\| ciphertext 279 - AEAD decryption input: AAD \|\| ciphertext \|\| authentication tag
280 280
281 The output buffer the user space caller provid 281 The output buffer the user space caller provides must be at least as
282 large to hold the following data: 282 large to hold the following data:
283 283
284 - AEAD encryption output: ciphertext \|\| aut 284 - AEAD encryption output: ciphertext \|\| authentication tag
285 285
286 - AEAD decryption output: plaintext 286 - AEAD decryption output: plaintext
287 287
288 Random Number Generator API 288 Random Number Generator API
289 --------------------------- 289 ---------------------------
290 290
291 Again, the operation is very similar to the ot 291 Again, the operation is very similar to the other APIs. During
292 initialization, the struct sockaddr data struc 292 initialization, the struct sockaddr data structure must be filled as
293 follows: 293 follows:
294 294
295 :: 295 ::
296 296
297 struct sockaddr_alg sa = { 297 struct sockaddr_alg sa = {
298 .salg_family = AF_ALG, 298 .salg_family = AF_ALG,
299 .salg_type = "rng", /* this selects th 299 .salg_type = "rng", /* this selects the random number generator */
300 .salg_name = "drbg_nopr_sha256" /* thi 300 .salg_name = "drbg_nopr_sha256" /* this is the RNG name */
301 }; 301 };
302 302
303 303
304 Depending on the RNG type, the RNG must be see 304 Depending on the RNG type, the RNG must be seeded. The seed is provided
305 using the setsockopt interface to set the key. 305 using the setsockopt interface to set the key. For example, the
306 ansi_cprng requires a seed. The DRBGs do not r 306 ansi_cprng requires a seed. The DRBGs do not require a seed, but may be
307 seeded. The seed is also known as a *Personali 307 seeded. The seed is also known as a *Personalization String* in NIST SP 800-90A
308 standard. 308 standard.
309 309
310 Using the read()/recvmsg() system calls, rando 310 Using the read()/recvmsg() system calls, random numbers can be obtained.
311 The kernel generates at most 128 bytes in one 311 The kernel generates at most 128 bytes in one call. If user space
312 requires more data, multiple calls to read()/r 312 requires more data, multiple calls to read()/recvmsg() must be made.
313 313
314 WARNING: The user space caller may invoke the 314 WARNING: The user space caller may invoke the initially mentioned accept
315 system call multiple times. In this case, the 315 system call multiple times. In this case, the returned file descriptors
316 have the same state. 316 have the same state.
317 317
318 Following CAVP testing interfaces are enabled 318 Following CAVP testing interfaces are enabled when kernel is built with
319 CRYPTO_USER_API_RNG_CAVP option: 319 CRYPTO_USER_API_RNG_CAVP option:
320 320
321 - the concatenation of *Entropy* and *Nonce* 321 - the concatenation of *Entropy* and *Nonce* can be provided to the RNG via
322 ALG_SET_DRBG_ENTROPY setsockopt interface. 322 ALG_SET_DRBG_ENTROPY setsockopt interface. Setting the entropy requires
323 CAP_SYS_ADMIN permission. 323 CAP_SYS_ADMIN permission.
324 324
325 - *Additional Data* can be provided using the 325 - *Additional Data* can be provided using the send()/sendmsg() system calls,
326 but only after the entropy has been set. 326 but only after the entropy has been set.
327 327
328 Zero-Copy Interface 328 Zero-Copy Interface
329 ------------------- 329 -------------------
330 330
331 In addition to the send/write/read/recv system 331 In addition to the send/write/read/recv system call family, the AF_ALG
332 interface can be accessed with the zero-copy i 332 interface can be accessed with the zero-copy interface of
333 splice/vmsplice. As the name indicates, the ke 333 splice/vmsplice. As the name indicates, the kernel tries to avoid a copy
334 operation into kernel space. 334 operation into kernel space.
335 335
336 The zero-copy operation requires data to be al 336 The zero-copy operation requires data to be aligned at the page
337 boundary. Non-aligned data can be used as well 337 boundary. Non-aligned data can be used as well, but may require more
338 operations of the kernel which would defeat th 338 operations of the kernel which would defeat the speed gains obtained
339 from the zero-copy interface. 339 from the zero-copy interface.
340 340
341 The system-inherent limit for the size of one 341 The system-inherent limit for the size of one zero-copy operation is 16
342 pages. If more data is to be sent to AF_ALG, u 342 pages. If more data is to be sent to AF_ALG, user space must slice the
343 input into segments with a maximum size of 16 343 input into segments with a maximum size of 16 pages.
344 344
345 Zero-copy can be used with the following code 345 Zero-copy can be used with the following code example (a complete
346 working example is provided with libkcapi): 346 working example is provided with libkcapi):
347 347
348 :: 348 ::
349 349
350 int pipes[2]; 350 int pipes[2];
351 351
352 pipe(pipes); 352 pipe(pipes);
353 /* input data in iov */ 353 /* input data in iov */
354 vmsplice(pipes[1], iov, iovlen, SPLICE_F_G 354 vmsplice(pipes[1], iov, iovlen, SPLICE_F_GIFT);
355 /* opfd is the file descriptor returned fr 355 /* opfd is the file descriptor returned from accept() system call */
356 splice(pipes[0], NULL, opfd, NULL, ret, 0) 356 splice(pipes[0], NULL, opfd, NULL, ret, 0);
357 read(opfd, out, outlen); 357 read(opfd, out, outlen);
358 358
359 359
360 Setsockopt Interface 360 Setsockopt Interface
361 -------------------- 361 --------------------
362 362
363 In addition to the read/recv and send/write sy 363 In addition to the read/recv and send/write system call handling to send
364 and retrieve data subject to the cipher operat 364 and retrieve data subject to the cipher operation, a consumer also needs
365 to set the additional information for the ciph 365 to set the additional information for the cipher operation. This
366 additional information is set using the setsoc 366 additional information is set using the setsockopt system call that must
367 be invoked with the file descriptor of the ope 367 be invoked with the file descriptor of the open cipher (i.e. the file
368 descriptor returned by the accept system call) 368 descriptor returned by the accept system call).
369 369
370 Each setsockopt invocation must use the level 370 Each setsockopt invocation must use the level SOL_ALG.
371 371
372 The setsockopt interface allows setting the fo 372 The setsockopt interface allows setting the following data using the
373 mentioned optname: 373 mentioned optname:
374 374
375 - ALG_SET_KEY -- Setting the key. Key setting 375 - ALG_SET_KEY -- Setting the key. Key setting is applicable to:
376 376
377 - the skcipher cipher type (symmetric ciph 377 - the skcipher cipher type (symmetric ciphers)
378 378
379 - the hash cipher type (keyed message dige 379 - the hash cipher type (keyed message digests)
380 380
381 - the AEAD cipher type 381 - the AEAD cipher type
382 382
383 - the RNG cipher type to provide the seed 383 - the RNG cipher type to provide the seed
384 384
385 - ALG_SET_KEY_BY_KEY_SERIAL -- Setting the key 385 - ALG_SET_KEY_BY_KEY_SERIAL -- Setting the key via keyring key_serial_t.
386 This operation behaves the same as ALG_SET_ 386 This operation behaves the same as ALG_SET_KEY. The decrypted
387 data is copied from a keyring key, and uses 387 data is copied from a keyring key, and uses that data as the
388 key for symmetric encryption. 388 key for symmetric encryption.
389 389
390 The passed in key_serial_t must have the KE 390 The passed in key_serial_t must have the KEY_(POS|USR|GRP|OTH)_SEARCH
391 permission set, otherwise -EPERM is returne 391 permission set, otherwise -EPERM is returned. Supports key types: user,
392 logon, encrypted, and trusted. 392 logon, encrypted, and trusted.
393 393
394 - ALG_SET_AEAD_AUTHSIZE -- Setting the authen 394 - ALG_SET_AEAD_AUTHSIZE -- Setting the authentication tag size for
395 AEAD ciphers. For a encryption operation, t 395 AEAD ciphers. For a encryption operation, the authentication tag of
396 the given size will be generated. For a dec 396 the given size will be generated. For a decryption operation, the
397 provided ciphertext is assumed to contain a 397 provided ciphertext is assumed to contain an authentication tag of
398 the given size (see section about AEAD memo 398 the given size (see section about AEAD memory layout below).
399 399
400 - ALG_SET_DRBG_ENTROPY -- Setting the entropy 400 - ALG_SET_DRBG_ENTROPY -- Setting the entropy of the random number generator.
401 This option is applicable to RNG cipher typ 401 This option is applicable to RNG cipher type only.
402 402
403 User space API example 403 User space API example
404 ---------------------- 404 ----------------------
405 405
406 Please see [1] for libkcapi which provides an 406 Please see [1] for libkcapi which provides an easy-to-use wrapper around
407 the aforementioned Netlink kernel interface. [ 407 the aforementioned Netlink kernel interface. [1] also contains a test
408 application that invokes all libkcapi API call 408 application that invokes all libkcapi API calls.
409 409
410 [1] https://www.chronox.de/libkcapi.html 410 [1] https://www.chronox.de/libkcapi.html
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