1 ENGINE 2 ====== 3 4 With OpenSSL 0.9.6, a new component was added to support alternative 5 cryptography implementations, most commonly for interfacing with external 6 crypto devices (eg. accelerator cards). This component is called ENGINE, 7 and its presence in OpenSSL 0.9.6 (and subsequent bug-fix releases) 8 caused a little confusion as 0.9.6** releases were rolled in two 9 versions, a "standard" and an "engine" version. In development for 0.9.7, 10 the ENGINE code has been merged into the main branch and will be present 11 in the standard releases from 0.9.7 forwards. 12 13 There are currently built-in ENGINE implementations for the following 14 crypto devices: 15 16 o Microsoft CryptoAPI 17 o VIA Padlock 18 o nCipher CHIL 19 20 In addition, dynamic binding to external ENGINE implementations is now 21 provided by a special ENGINE called "dynamic". See the "DYNAMIC ENGINE" 22 section below for details. 23 24 At this stage, a number of things are still needed and are being worked on: 25 26 1 Integration of EVP support. 27 2 Configuration support. 28 3 Documentation! 29 301 With respect to EVP, this relates to support for ciphers and digests in 31 the ENGINE model so that alternative implementations of existing 32 algorithms/modes (or previously unimplemented ones) can be provided by 33 ENGINE implementations. 34 352 Configuration support currently exists in the ENGINE API itself, in the 36 form of "control commands". These allow an application to expose to the 37 user/admin the set of commands and parameter types a given ENGINE 38 implementation supports, and for an application to directly feed string 39 based input to those ENGINEs, in the form of name-value pairs. This is an 40 extensible way for ENGINEs to define their own "configuration" mechanisms 41 that are specific to a given ENGINE (eg. for a particular hardware 42 device) but that should be consistent across *all* OpenSSL-based 43 applications when they use that ENGINE. Work is in progress (or at least 44 in planning) for supporting these control commands from the CONF (or 45 NCONF) code so that applications using OpenSSL's existing configuration 46 file format can have ENGINE settings specified in much the same way. 47 Presently however, applications must use the ENGINE API itself to provide 48 such functionality. To see first hand the types of commands available 49 with the various compiled-in ENGINEs (see further down for dynamic 50 ENGINEs), use the "engine" openssl utility with full verbosity, ie; 51 openssl engine -vvvv 52 533 Documentation? Volunteers welcome! The source code is reasonably well 54 self-documenting, but some summaries and usage instructions are needed - 55 moreover, they are needed in the same POD format the existing OpenSSL 56 documentation is provided in. Any complete or incomplete contributions 57 would help make this happen. 58 59 STABILITY & BUG-REPORTS 60 ======================= 61 62 What already exists is fairly stable as far as it has been tested, but 63 the test base has been a bit small most of the time. For the most part, 64 the vendors of the devices these ENGINEs support have contributed to the 65 development and/or testing of the implementations, and *usually* (with no 66 guarantees) have experience in using the ENGINE support to drive their 67 devices from common OpenSSL-based applications. Bugs and/or inexplicable 68 behaviour in using a specific ENGINE implementation should be sent to the 69 author of that implementation (if it is mentioned in the corresponding C 70 file), and in the case of implementations for commercial hardware 71 devices, also through whatever vendor support channels are available. If 72 none of this is possible, or the problem seems to be something about the 73 ENGINE API itself (ie. not necessarily specific to a particular ENGINE 74 implementation) then you should mail complete details to the relevant 75 OpenSSL mailing list. For a definition of "complete details", refer to 76 the OpenSSL "README" file. As for which list to send it to; 77 78 openssl-users: if you are *using* the ENGINE abstraction, either in an 79 pre-compiled application or in your own application code. 80 81 openssl-dev: if you are discussing problems with OpenSSL source code. 82 83 USAGE 84 ===== 85 86 The default "openssl" ENGINE is always chosen when performing crypto 87 operations unless you specify otherwise. You must actively tell the 88 openssl utility commands to use anything else through a new command line 89 switch called "-engine". Also, if you want to use the ENGINE support in 90 your own code to do something similar, you must likewise explicitly 91 select the ENGINE implementation you want. 92 93 Depending on the type of hardware, system, and configuration, "settings" 94 may need to be applied to an ENGINE for it to function as expected/hoped. 95 The recommended way of doing this is for the application to support 96 ENGINE "control commands" so that each ENGINE implementation can provide 97 whatever configuration primitives it might require and the application 98 can allow the user/admin (and thus the hardware vendor's support desk 99 also) to provide any such input directly to the ENGINE implementation. 100 This way, applications do not need to know anything specific to any 101 device, they only need to provide the means to carry such user/admin 102 input through to the ENGINE in question. Ie. this connects *you* (and 103 your helpdesk) to the specific ENGINE implementation (and device), and 104 allows application authors to not get buried in hassle supporting 105 arbitrary devices they know (and care) nothing about. 106 107 A new "openssl" utility, "openssl engine", has been added in that allows 108 for testing and examination of ENGINE implementations. Basic usage 109 instructions are available by specifying the "-?" command line switch. 110 111 DYNAMIC ENGINES 112 =============== 113 114 The new "dynamic" ENGINE provides a low-overhead way to support ENGINE 115 implementations that aren't pre-compiled and linked into OpenSSL-based 116 applications. This could be because existing compiled-in implementations 117 have known problems and you wish to use a newer version with an existing 118 application. It could equally be because the application (or OpenSSL 119 library) you are using simply doesn't have support for the ENGINE you 120 wish to use, and the ENGINE provider (eg. hardware vendor) is providing 121 you with a self-contained implementation in the form of a shared-library. 122 The other use-case for "dynamic" is with applications that wish to 123 maintain the smallest foot-print possible and so do not link in various 124 ENGINE implementations from OpenSSL, but instead leaves you to provide 125 them, if you want them, in the form of "dynamic"-loadable 126 shared-libraries. It should be possible for hardware vendors to provide 127 their own shared-libraries to support arbitrary hardware to work with 128 applications based on OpenSSL 0.9.7 or later. If you're using an 129 application based on 0.9.7 (or later) and the support you desire is only 130 announced for versions later than the one you need, ask the vendor to 131 backport their ENGINE to the version you need. 132 133 How does "dynamic" work? 134 ------------------------ 135 The dynamic ENGINE has a special flag in its implementation such that 136 every time application code asks for the 'dynamic' ENGINE, it in fact 137 gets its own copy of it. As such, multi-threaded code (or code that 138 multiplexes multiple uses of 'dynamic' in a single application in any 139 way at all) does not get confused by 'dynamic' being used to do many 140 independent things. Other ENGINEs typically don't do this so there is 141 only ever 1 ENGINE structure of its type (and reference counts are used 142 to keep order). The dynamic ENGINE itself provides absolutely no 143 cryptographic functionality, and any attempt to "initialise" the ENGINE 144 automatically fails. All it does provide are a few "control commands" 145 that can be used to control how it will load an external ENGINE 146 implementation from a shared-library. To see these control commands, 147 use the command-line; 148 149 openssl engine -vvvv dynamic 150 151 The "SO_PATH" control command should be used to identify the 152 shared-library that contains the ENGINE implementation, and "NO_VCHECK" 153 might possibly be useful if there is a minor version conflict and you 154 (or a vendor helpdesk) is convinced you can safely ignore it. 155 "ID" is probably only needed if a shared-library implements 156 multiple ENGINEs, but if you know the engine id you expect to be using, 157 it doesn't hurt to specify it (and this provides a sanity check if 158 nothing else). "LIST_ADD" is only required if you actually wish the 159 loaded ENGINE to be discoverable by application code later on using the 160 ENGINE's "id". For most applications, this isn't necessary - but some 161 application authors may have nifty reasons for using it. The "LOAD" 162 command is the only one that takes no parameters and is the command 163 that uses the settings from any previous commands to actually *load* 164 the shared-library ENGINE implementation. If this command succeeds, the 165 (copy of the) 'dynamic' ENGINE will magically morph into the ENGINE 166 that has been loaded from the shared-library. As such, any control 167 commands supported by the loaded ENGINE could then be executed as per 168 normal. Eg. if ENGINE "foo" is implemented in the shared-library 169 "libfoo.so" and it supports some special control command "CMD_FOO", the 170 following code would load and use it (NB: obviously this code has no 171 error checking); 172 173 ENGINE *e = ENGINE_by_id("dynamic"); 174 ENGINE_ctrl_cmd_string(e, "SO_PATH", "/lib/libfoo.so", 0); 175 ENGINE_ctrl_cmd_string(e, "ID", "foo", 0); 176 ENGINE_ctrl_cmd_string(e, "LOAD", NULL, 0); 177 ENGINE_ctrl_cmd_string(e, "CMD_FOO", "some input data", 0); 178 179 For testing, the "openssl engine" utility can be useful for this sort 180 of thing. For example the above code excerpt would achieve much the 181 same result as; 182 183 openssl engine dynamic \ 184 -pre SO_PATH:/lib/libfoo.so \ 185 -pre ID:foo \ 186 -pre LOAD \ 187 -pre "CMD_FOO:some input data" 188 189 Or to simply see the list of commands supported by the "foo" ENGINE; 190 191 openssl engine -vvvv dynamic \ 192 -pre SO_PATH:/lib/libfoo.so \ 193 -pre ID:foo \ 194 -pre LOAD 195 196 Applications that support the ENGINE API and more specifically, the 197 "control commands" mechanism, will provide some way for you to pass 198 such commands through to ENGINEs. As such, you would select "dynamic" 199 as the ENGINE to use, and the parameters/commands you pass would 200 control the *actual* ENGINE used. Each command is actually a name-value 201 pair and the value can sometimes be omitted (eg. the "LOAD" command). 202 Whilst the syntax demonstrated in "openssl engine" uses a colon to 203 separate the command name from the value, applications may provide 204 their own syntax for making that separation (eg. a win32 registry 205 key-value pair may be used by some applications). The reason for the 206 "-pre" syntax in the "openssl engine" utility is that some commands 207 might be issued to an ENGINE *after* it has been initialised for use. 208 Eg. if an ENGINE implementation requires a smart-card to be inserted 209 during initialisation (or a PIN to be typed, or whatever), there may be 210 a control command you can issue afterwards to "forget" the smart-card 211 so that additional initialisation is no longer possible. In 212 applications such as web-servers, where potentially volatile code may 213 run on the same host system, this may provide some arguable security 214 value. In such a case, the command would be passed to the ENGINE after 215 it has been initialised for use, and so the "-post" switch would be 216 used instead. Applications may provide a different syntax for 217 supporting this distinction, and some may simply not provide it at all 218 ("-pre" is almost always what you're after, in reality). 219 220 How do I build a "dynamic" ENGINE? 221 ---------------------------------- 222 This question is trickier - currently OpenSSL bundles various ENGINE 223 implementations that are statically built in, and any application that 224 calls the "ENGINE_load_builtin_engines()" function will automatically 225 have all such ENGINEs available (and occupying memory). Applications 226 that don't call that function have no ENGINEs available like that and 227 would have to use "dynamic" to load any such ENGINE - but on the other 228 hand such applications would only have the memory footprint of any 229 ENGINEs explicitly loaded using user/admin provided control commands. 230 The main advantage of not statically linking ENGINEs and only using 231 "dynamic" for hardware support is that any installation using no 232 "external" ENGINE suffers no unnecessary memory footprint from unused 233 ENGINEs. Likewise, installations that do require an ENGINE incur the 234 overheads from only *that* ENGINE once it has been loaded. 235 236 Sounds good? Maybe, but currently building an ENGINE implementation as 237 a shared-library that can be loaded by "dynamic" isn't automated in 238 OpenSSL's build process. It can be done manually quite easily however. 239 Such a shared-library can either be built with any OpenSSL code it 240 needs statically linked in, or it can link dynamically against OpenSSL 241 if OpenSSL itself is built as a shared library. The instructions are 242 the same in each case, but in the former (statically linked any 243 dependencies on OpenSSL) you must ensure OpenSSL is built with 244 position-independent code ("PIC"). The default OpenSSL compilation may 245 already specify the relevant flags to do this, but you should consult 246 with your compiler documentation if you are in any doubt. 247 248 This example will show building the "atalla" ENGINE in the 249 crypto/engine/ directory as a shared-library for use via the "dynamic" 250 ENGINE. 251 1) "cd" to the crypto/engine/ directory of a pre-compiled OpenSSL 252 source tree. 253 2) Recompile at least one source file so you can see all the compiler 254 flags (and syntax) being used to build normally. Eg; 255 touch hw_atalla.c ; make 256 will rebuild "hw_atalla.o" using all such flags. 257 3) Manually enter the same compilation line to compile the 258 "hw_atalla.c" file but with the following two changes; 259 (a) add "-DENGINE_DYNAMIC_SUPPORT" to the command line switches, 260 (b) change the output file from "hw_atalla.o" to something new, 261 eg. "tmp_atalla.o" 262 4) Link "tmp_atalla.o" into a shared-library using the top-level 263 OpenSSL libraries to resolve any dependencies. The syntax for doing 264 this depends heavily on your system/compiler and is a nightmare 265 known well to anyone who has worked with shared-library portability 266 before. 'gcc' on Linux, for example, would use the following syntax; 267 gcc -shared -o dyn_atalla.so tmp_atalla.o -L../.. -lcrypto 268 5) Test your shared library using "openssl engine" as explained in the 269 previous section. Eg. from the top-level directory, you might try; 270 apps/openssl engine -vvvv dynamic \ 271 -pre SO_PATH:./crypto/engine/dyn_atalla.so -pre LOAD 272 If the shared-library loads successfully, you will see both "-pre" 273 commands marked as "SUCCESS" and the list of control commands 274 displayed (because of "-vvvv") will be the control commands for the 275 *atalla* ENGINE (ie. *not* the 'dynamic' ENGINE). You can also add 276 the "-t" switch to the utility if you want it to try and initialise 277 the atalla ENGINE for use to test any possible hardware/driver 278 issues. 279 280 PROBLEMS 281 ======== 282 283 It seems like the ENGINE part doesn't work too well with CryptoSwift on Win32. 284 A quick test done right before the release showed that trying "openssl speed 285 -engine cswift" generated errors. If the DSO gets enabled, an attempt is made 286 to write at memory address 0x00000002. 287 288