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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 CryptoSwift
17 o Compaq Atalla
18 o nCipher CHIL
19 o Nuron
20 o Broadcom uBSec
22 In addition, dynamic binding to external ENGINE implementations is now
23 provided by a special ENGINE called "dynamic". See the "DYNAMIC ENGINE"
24 section below for details.
26 At this stage, a number of things are still needed and are being worked on:
28 1 Integration of EVP support.
29 2 Configuration support.
30 3 Documentation!
32 1 With respect to EVP, this relates to support for ciphers and digests in
33 the ENGINE model so that alternative implementations of existing
34 algorithms/modes (or previously unimplemented ones) can be provided by
35 ENGINE implementations.
37 2 Configuration support currently exists in the ENGINE API itself, in the
38 form of "control commands". These allow an application to expose to the
39 user/admin the set of commands and parameter types a given ENGINE
40 implementation supports, and for an application to directly feed string
41 based input to those ENGINEs, in the form of name-value pairs. This is an
42 extensible way for ENGINEs to define their own "configuration" mechanisms
43 that are specific to a given ENGINE (eg. for a particular hardware
44 device) but that should be consistent across *all* OpenSSL-based
45 applications when they use that ENGINE. Work is in progress (or at least
46 in planning) for supporting these control commands from the CONF (or
47 NCONF) code so that applications using OpenSSL's existing configuration
48 file format can have ENGINE settings specified in much the same way.
49 Presently however, applications must use the ENGINE API itself to provide
50 such functionality. To see first hand the types of commands available
51 with the various compiled-in ENGINEs (see further down for dynamic
52 ENGINEs), use the "engine" openssl utility with full verbosity, ie;
53 openssl engine -vvvv
55 3 Documentation? Volunteers welcome! The source code is reasonably well
56 self-documenting, but some summaries and usage instructions are needed -
57 moreover, they are needed in the same POD format the existing OpenSSL
58 documentation is provided in. Any complete or incomplete contributions
59 would help make this happen.
61 STABILITY & BUG-REPORTS
64 What already exists is fairly stable as far as it has been tested, but
65 the test base has been a bit small most of the time. For the most part,
66 the vendors of the devices these ENGINEs support have contributed to the
67 development and/or testing of the implementations, and *usually* (with no
68 guarantees) have experience in using the ENGINE support to drive their
69 devices from common OpenSSL-based applications. Bugs and/or inexplicable
70 behaviour in using a specific ENGINE implementation should be sent to the
71 author of that implementation (if it is mentioned in the corresponding C
72 file), and in the case of implementations for commercial hardware
73 devices, also through whatever vendor support channels are available. If
74 none of this is possible, or the problem seems to be something about the
75 ENGINE API itself (ie. not necessarily specific to a particular ENGINE
76 implementation) then you should mail complete details to the relevant
77 OpenSSL mailing list. For a definition of "complete details", refer to
78 the OpenSSL "README" file. As for which list to send it to;
80 openssl-users: if you are *using* the ENGINE abstraction, either in an
81 pre-compiled application or in your own application code.
83 openssl-dev: if you are discussing problems with OpenSSL source code.
88 The default "openssl" ENGINE is always chosen when performing crypto
89 operations unless you specify otherwise. You must actively tell the
90 openssl utility commands to use anything else through a new command line
91 switch called "-engine". Also, if you want to use the ENGINE support in
92 your own code to do something similar, you must likewise explicitly
93 select the ENGINE implementation you want.
95 Depending on the type of hardware, system, and configuration, "settings"
96 may need to be applied to an ENGINE for it to function as expected/hoped.
97 The recommended way of doing this is for the application to support
98 ENGINE "control commands" so that each ENGINE implementation can provide
99 whatever configuration primitives it might require and the application
100 can allow the user/admin (and thus the hardware vendor's support desk
101 also) to provide any such input directly to the ENGINE implementation.
102 This way, applications do not need to know anything specific to any
103 device, they only need to provide the means to carry such user/admin
104 input through to the ENGINE in question. Ie. this connects *you* (and
105 your helpdesk) to the specific ENGINE implementation (and device), and
106 allows application authors to not get buried in hassle supporting
107 arbitrary devices they know (and care) nothing about.
109 A new "openssl" utility, "openssl engine", has been added in that allows
110 for testing and examination of ENGINE implementations. Basic usage
111 instructions are available by specifying the "-?" command line switch.
113 DYNAMIC ENGINES
116 The new "dynamic" ENGINE provides a low-overhead way to support ENGINE
117 implementations that aren't pre-compiled and linked into OpenSSL-based
118 applications. This could be because existing compiled-in implementations
119 have known problems and you wish to use a newer version with an existing
120 application. It could equally be because the application (or OpenSSL
121 library) you are using simply doesn't have support for the ENGINE you
122 wish to use, and the ENGINE provider (eg. hardware vendor) is providing
123 you with a self-contained implementation in the form of a shared-library.
124 The other use-case for "dynamic" is with applications that wish to
125 maintain the smallest foot-print possible and so do not link in various
126 ENGINE implementations from OpenSSL, but instead leaves you to provide
127 them, if you want them, in the form of "dynamic"-loadable
128 shared-libraries. It should be possible for hardware vendors to provide
129 their own shared-libraries to support arbitrary hardware to work with
130 applications based on OpenSSL 0.9.7 or later. If you're using an
131 application based on 0.9.7 (or later) and the support you desire is only
132 announced for versions later than the one you need, ask the vendor to
133 backport their ENGINE to the version you need.
135 How does "dynamic" work?
137 The dynamic ENGINE has a special flag in its implementation such that
138 every time application code asks for the 'dynamic' ENGINE, it in fact
139 gets its own copy of it. As such, multi-threaded code (or code that
140 multiplexes multiple uses of 'dynamic' in a single application in any
141 way at all) does not get confused by 'dynamic' being used to do many
142 independent things. Other ENGINEs typically don't do this so there is
143 only ever 1 ENGINE structure of its type (and reference counts are used
144 to keep order). The dynamic ENGINE itself provides absolutely no
145 cryptographic functionality, and any attempt to "initialise" the ENGINE
146 automatically fails. All it does provide are a few "control commands"
147 that can be used to control how it will load an external ENGINE
148 implementation from a shared-library. To see these control commands,
149 use the command-line;
151 openssl engine -vvvv dynamic
153 The "SO_PATH" control command should be used to identify the
154 shared-library that contains the ENGINE implementation, and "NO_VCHECK"
155 might possibly be useful if there is a minor version conflict and you
156 (or a vendor helpdesk) is convinced you can safely ignore it.
157 "ID" is probably only needed if a shared-library implements
158 multiple ENGINEs, but if you know the engine id you expect to be using,
159 it doesn't hurt to specify it (and this provides a sanity check if
160 nothing else). "LIST_ADD" is only required if you actually wish the
161 loaded ENGINE to be discoverable by application code later on using the
162 ENGINE's "id". For most applications, this isn't necessary - but some
163 application authors may have nifty reasons for using it. The "LOAD"
164 command is the only one that takes no parameters and is the command
165 that uses the settings from any previous commands to actually *load*
166 the shared-library ENGINE implementation. If this command succeeds, the
167 (copy of the) 'dynamic' ENGINE will magically morph into the ENGINE
168 that has been loaded from the shared-library. As such, any control
169 commands supported by the loaded ENGINE could then be executed as per
170 normal. Eg. if ENGINE "foo" is implemented in the shared-library
171 "libfoo.so" and it supports some special control command "CMD_FOO", the
172 following code would load and use it (NB: obviously this code has no
173 error checking);
175 ENGINE *e = ENGINE_by_id("dynamic");
176 ENGINE_ctrl_cmd_string(e, "SO_PATH", "/lib/libfoo.so", 0);
177 ENGINE_ctrl_cmd_string(e, "ID", "foo", 0);
178 ENGINE_ctrl_cmd_string(e, "LOAD", NULL, 0);
179 ENGINE_ctrl_cmd_string(e, "CMD_FOO", "some input data", 0);
181 For testing, the "openssl engine" utility can be useful for this sort
182 of thing. For example the above code excerpt would achieve much the
183 same result as;
185 openssl engine dynamic \
186 -pre SO_PATH:/lib/libfoo.so \
187 -pre ID:foo \
188 -pre LOAD \
189 -pre "CMD_FOO:some input data"
191 Or to simply see the list of commands supported by the "foo" ENGINE;
193 openssl engine -vvvv dynamic \
194 -pre SO_PATH:/lib/libfoo.so \
195 -pre ID:foo \
196 -pre LOAD
198 Applications that support the ENGINE API and more specifically, the
199 "control commands" mechanism, will provide some way for you to pass
200 such commands through to ENGINEs. As such, you would select "dynamic"
201 as the ENGINE to use, and the parameters/commands you pass would
202 control the *actual* ENGINE used. Each command is actually a name-value
203 pair and the value can sometimes be omitted (eg. the "LOAD" command).
204 Whilst the syntax demonstrated in "openssl engine" uses a colon to
205 separate the command name from the value, applications may provide
206 their own syntax for making that separation (eg. a win32 registry
207 key-value pair may be used by some applications). The reason for the
208 "-pre" syntax in the "openssl engine" utility is that some commands
209 might be issued to an ENGINE *after* it has been initialised for use.
210 Eg. if an ENGINE implementation requires a smart-card to be inserted
211 during initialisation (or a PIN to be typed, or whatever), there may be
212 a control command you can issue afterwards to "forget" the smart-card
213 so that additional initialisation is no longer possible. In
214 applications such as web-servers, where potentially volatile code may
215 run on the same host system, this may provide some arguable security
216 value. In such a case, the command would be passed to the ENGINE after
217 it has been initialised for use, and so the "-post" switch would be
218 used instead. Applications may provide a different syntax for
219 supporting this distinction, and some may simply not provide it at all
220 ("-pre" is almost always what you're after, in reality).
222 How do I build a "dynamic" ENGINE?
224 This question is trickier - currently OpenSSL bundles various ENGINE
225 implementations that are statically built in, and any application that
226 calls the "ENGINE_load_builtin_engines()" function will automatically
227 have all such ENGINEs available (and occupying memory). Applications
228 that don't call that function have no ENGINEs available like that and
229 would have to use "dynamic" to load any such ENGINE - but on the other
230 hand such applications would only have the memory footprint of any
231 ENGINEs explicitly loaded using user/admin provided control commands.
232 The main advantage of not statically linking ENGINEs and only using
233 "dynamic" for hardware support is that any installation using no
234 "external" ENGINE suffers no unnecessary memory footprint from unused
235 ENGINEs. Likewise, installations that do require an ENGINE incur the
236 overheads from only *that* ENGINE once it has been loaded.
238 Sounds good? Maybe, but currently building an ENGINE implementation as
239 a shared-library that can be loaded by "dynamic" isn't automated in
240 OpenSSL's build process. It can be done manually quite easily however.
241 Such a shared-library can either be built with any OpenSSL code it
242 needs statically linked in, or it can link dynamically against OpenSSL
243 if OpenSSL itself is built as a shared library. The instructions are
244 the same in each case, but in the former (statically linked any
245 dependencies on OpenSSL) you must ensure OpenSSL is built with
246 position-independent code ("PIC"). The default OpenSSL compilation may
247 already specify the relevant flags to do this, but you should consult
248 with your compiler documentation if you are in any doubt.
250 This example will show building the "atalla" ENGINE in the
251 crypto/engine/ directory as a shared-library for use via the "dynamic"
253 1) "cd" to the crypto/engine/ directory of a pre-compiled OpenSSL
254 source tree.
255 2) Recompile at least one source file so you can see all the compiler
256 flags (and syntax) being used to build normally. Eg;
257 touch hw_atalla.c ; make
258 will rebuild "hw_atalla.o" using all such flags.
259 3) Manually enter the same compilation line to compile the
260 "hw_atalla.c" file but with the following two changes;
261 (a) add "-DENGINE_DYNAMIC_SUPPORT" to the command line switches,
262 (b) change the output file from "hw_atalla.o" to something new,
263 eg. "tmp_atalla.o"
264 4) Link "tmp_atalla.o" into a shared-library using the top-level
265 OpenSSL libraries to resolve any dependencies. The syntax for doing
266 this depends heavily on your system/compiler and is a nightmare
267 known well to anyone who has worked with shared-library portability
268 before. 'gcc' on Linux, for example, would use the following syntax;
269 gcc -shared -o dyn_atalla.so tmp_atalla.o -L../.. -lcrypto
270 5) Test your shared library using "openssl engine" as explained in the
271 previous section. Eg. from the top-level directory, you might try;
272 apps/openssl engine -vvvv dynamic \
273 -pre SO_PATH:./crypto/engine/dyn_atalla.so -pre LOAD
274 If the shared-library loads successfully, you will see both "-pre"
275 commands marked as "SUCCESS" and the list of control commands
276 displayed (because of "-vvvv") will be the control commands for the
277 *atalla* ENGINE (ie. *not* the 'dynamic' ENGINE). You can also add
278 the "-t" switch to the utility if you want it to try and initialise
279 the atalla ENGINE for use to test any possible hardware/driver
285 It seems like the ENGINE part doesn't work too well with CryptoSwift on Win32.
286 A quick test done right before the release showed that trying "openssl speed
287 -engine cswift" generated errors. If the DSO gets enabled, an attempt is made
288 to write at memory address 0x00000002.