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
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.
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;
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.
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STABILITY & BUG-REPORTS
62
=======================
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What already exists is fairly stable as far as it has been tested, but
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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
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devices from common OpenSSL-based applications. Bugs and/or inexplicable
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behaviour in using a specific ENGINE implementation should be sent to the
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author of that implementation (if it is mentioned in the corresponding C
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file), and in the case of implementations for commercial hardware
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devices, also through whatever vendor support channels are available. If
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none of this is possible, or the problem seems to be something about the
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ENGINE API itself (ie. not necessarily specific to a particular ENGINE
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implementation) then you should mail complete details to the relevant
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OpenSSL mailing list. For a definition of "complete details", refer to
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the OpenSSL "README" file. As for which list to send it to;
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openssl-users: if you are *using* the ENGINE abstraction, either in an
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pre-compiled application or in your own application code.
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openssl-dev: if you are discussing problems with OpenSSL source code.
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The default "openssl" ENGINE is always chosen when performing crypto
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operations unless you specify otherwise. You must actively tell the
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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
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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.
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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.
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?
136
------------------------
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
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
185
openssl engine dynamic \
186
-pre SO_PATH:/lib/libfoo.so \
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 \
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).
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How do I build a "dynamic" ENGINE?
223
----------------------------------
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
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,
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.
added
removed
README.ENGINE
