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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.
13 There are currently built-in ENGINE implementations for the following
14 crypto devices:
16 o Microsoft CryptoAPI
17 o VIA Padlock
18 o nCipher CHIL
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.
24 At this stage, a number of things are still needed and are being worked on:
26 1 Integration of EVP support.
27 2 Configuration support.
28 3 Documentation!
30 1 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.
35 2 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
53 3 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.
59 STABILITY & BUG-REPORTS
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;
78 openssl-users: if you are *using* the ENGINE abstraction, either in an
79 pre-compiled application or in your own application code.
81 openssl-dev: if you are discussing problems with OpenSSL source code.
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.
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.
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.
111 DYNAMIC ENGINES
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.
133 How does "dynamic" work?
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;
149 openssl engine -vvvv dynamic
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);
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);
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;
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"
189 Or to simply see the list of commands supported by the "foo" ENGINE;
191 openssl engine -vvvv dynamic \
192 -pre SO_PATH:/lib/libfoo.so \
193 -pre ID:foo \
194 -pre LOAD
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).
220 How do I build a "dynamic" ENGINE?
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.
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.
248 This example will show building the "atalla" ENGINE in the
249 crypto/engine/ directory as a shared-library for use via the "dynamic"
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
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.