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 CryptoSwift
17      o Compaq Atalla
18      o nCipher CHIL
19      o Nuron
20      o Broadcom uBSec
21
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.
25
26  At this stage, a number of things are still needed and are being worked on:
27
28      1 Integration of EVP support.
29      2 Configuration support.
30      3 Documentation!
31
321 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.
36
372 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
54
553 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.
60
61  STABILITY & BUG-REPORTS
62  =======================
63
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;
79
80     openssl-users: if you are *using* the ENGINE abstraction, either in an
81          pre-compiled application or in your own application code.
82
83     openssl-dev: if you are discussing problems with OpenSSL source code.
84
85  USAGE
86  =====
87
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.
94
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.
108
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.
112
113  DYNAMIC ENGINES
114  ===============
115
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.
134
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;
150
151       openssl engine -vvvv dynamic
152
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);
174
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);
180
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;
184
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"
190
191    Or to simply see the list of commands supported by the "foo" ENGINE;
192
193       openssl engine -vvvv dynamic \
194                 -pre SO_PATH:/lib/libfoo.so \
195                 -pre ID:foo \
196                 -pre LOAD
197
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).
221
222  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.
237
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.
249
250    This example will show building the "atalla" ENGINE in the
251    crypto/engine/ directory as a shared-library for use via the "dynamic"
252    ENGINE.
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
280       issues.
281
282  PROBLEMS
283  ========
284
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.
289
290