-
ENGINE
======
- With OpenSSL 0.9.6, a new component has been added to support external
- crypto devices, for example accelerator cards. The component is called
- ENGINE, and has still a pretty experimental status and almost no
- documentation. It's designed to be faily easily extensible by the
- calling programs.
+ With OpenSSL 0.9.6, a new component was added to support alternative
+ cryptography implementations, most commonly for interfacing with external
+ crypto devices (eg. accelerator cards). This component is called ENGINE,
+ and its presence in OpenSSL 0.9.6 (and subsequent bug-fix releases)
+ caused a little confusion as 0.9.6** releases were rolled in two
+ versions, a "standard" and an "engine" verion. In development for 0.9.7,
+ the ENGINE code has been merged into the main branch and will be present
+ in the standard releases from 0.9.7 forwards.
- There's currently built-in support for the following crypto devices:
+ There are currently built-in ENGINE implementations for the following
+ crypto devices:
o CryptoSwift
o Compaq Atalla
o nCipher CHIL
o Nuron
+ o Broadcom uBSec
+
+ In addition, dynamic binding to external ENGINE implementations is now
+ provided by a special ENGINE called "dynamic". See the "DYNAMIC ENGINE"
+ section below for details.
+
+ At this stage, a number of things are still needed and are being worked on:
+
+ 1 Integration of EVP support.
+ 2 Configuration support.
+ 3 Documentation!
+
+1 With respect to EVP, this relates to support for ciphers and digests in
+ the ENGINE model so that alternative implementations of existing
+ algorithms/modes (or previously unimplemented ones) can be provided by
+ ENGINE implementations.
+
+2 Configuration support currently exists in the ENGINE API itself, in the
+ form of "control commands". These allow an application to expose to the
+ user/admin the set of commands and parameter types a given ENGINE
+ implementation supports, and for an application to directly feed string
+ based input to those ENGINEs, in the form of name-value pairs. This is an
+ extensible way for ENGINEs to define their own "configuration" mechanisms
+ that are specific to a given ENGINE (eg. for a particular hardware
+ device) but that should be consistent across *all* OpenSSL-based
+ applications when they use that ENGINE. Work is in progress (or at least
+ in planning) for supporting these control commands from the CONF (or
+ NCONF) code so that applications using OpenSSL's existing configuration
+ file format can have ENGINE settings specified in much the same way.
+ Presently however, applications must use the ENGINE API itself to provide
+ such functionality. To see first hand the types of commands available
+ with the various compiled-in ENGINEs (see further down for dynamic
+ ENGINEs), use the "engine" openssl utility with full verbosity, ie;
+ openssl engine -vvvv
- A number of things are still needed and are being worked on:
+3 Documentation? Volunteers welcome! The source code is reasonably well
+ self-documenting, but some summaries and usage instructions are needed -
+ moreover, they are needed in the same POD format the existing OpenSSL
+ documentation is provided in. Any complete or incomplete contributions
+ would help make this happen.
- o A better way of handling the methods that are handled by the
- engines.
- o Documentation!
+ STABILITY & BUG-REPORTS
+ =======================
What already exists is fairly stable as far as it has been tested, but
- the test base has been a bit small most of the time.
+ the test base has been a bit small most of the time. For the most part,
+ the vendors of the devices these ENGINEs support have contributed to the
+ development and/or testing of the implementations, and *usually* (with no
+ guarantees) have experience in using the ENGINE support to drive their
+ devices from common OpenSSL-based applications. Bugs and/or inexplicable
+ behaviour in using a specific ENGINE implementation should be sent to the
+ author of that implementation (if it is mentioned in the corresponding C
+ file), and in the case of implementations for commercial hardware
+ devices, also through whatever vendor support channels are available. If
+ none of this is possible, or the problem seems to be something about the
+ ENGINE API itself (ie. not necessarily specific to a particular ENGINE
+ implementation) then you should mail complete details to the relevant
+ OpenSSL mailing list. For a definition of "complete details", refer to
+ the OpenSSL "README" file. As for which list to send it to;
+
+ openssl-users: if you are *using* the ENGINE abstraction, either in an
+ pre-compiled application or in your own application code.
+
+ openssl-dev: if you are discussing problems with OpenSSL source code.
+
+ USAGE
+ =====
+
+ The default "openssl" ENGINE is always chosen when performing crypto
+ operations unless you specify otherwise. You must actively tell the
+ openssl utility commands to use anything else through a new command line
+ switch called "-engine". Also, if you want to use the ENGINE support in
+ your own code to do something similar, you must likewise explicitly
+ select the ENGINE implementation you want.
+
+ Depending on the type of hardware, system, and configuration, "settings"
+ may need to be applied to an ENGINE for it to function as expected/hoped.
+ The recommended way of doing this is for the application to support
+ ENGINE "control commands" so that each ENGINE implementation can provide
+ whatever configuration primitives it might require and the application
+ can allow the user/admin (and thus the hardware vendor's support desk
+ also) to provide any such input directly to the ENGINE implementation.
+ This way, applications do not need to know anything specific to any
+ device, they only need to provide the means to carry such user/admin
+ input through to the ENGINE in question. Ie. this connects *you* (and
+ your helpdesk) to the specific ENGINE implementation (and device), and
+ allows application authors to not get buried in hassle supporting
+ arbitrary devices they know (and care) nothing about.
+
+ A new "openssl" utility, "openssl engine", has been added in that allows
+ for testing and examination of ENGINE implementations. Basic usage
+ instructions are available by specifying the "-?" command line switch.
+
+ DYNAMIC ENGINES
+ ===============
+
+ The new "dynamic" ENGINE provides a low-overhead way to support ENGINE
+ implementations that aren't pre-compiled and linked into OpenSSL-based
+ applications. This could be because existing compiled-in implementations
+ have known problems and you wish to use a newer version with an existing
+ application. It could equally be because the application (or OpenSSL
+ library) you are using simply doesn't have support for the ENGINE you
+ wish to use, and the ENGINE provider (eg. hardware vendor) is providing
+ you with a self-contained implementation in the form of a shared-library.
+ The other use-case for "dynamic" is with applications that wish to
+ maintain the smallest foot-print possible and so do not link in various
+ ENGINE implementations from OpenSSL, but instead leaves you to provide
+ them, if you want them, in the form of "dynamic"-loadable
+ shared-libraries. It should be possible for hardware vendors to provide
+ their own shared-libraries to support arbitrary hardware to work with
+ applications based on OpenSSL 0.9.7 or later. If you're using an
+ application based on 0.9.7 (or later) and the support you desire is only
+ announced for versions later than the one you need, ask the vendor to
+ backport their ENGINE to the version you need.
+
+ How does "dynamic" work?
+ ------------------------
+ The dynamic ENGINE has a special flag in its implementation such that
+ every time application code asks for the 'dynamic' ENGINE, it in fact
+ gets its own copy of it. As such, multi-threaded code (or code that
+ multiplexes multiple uses of 'dynamic' in a single application in any
+ way at all) does not get confused by 'dynamic' being used to do many
+ independant things. Other ENGINEs typically don't do this so there is
+ only ever 1 ENGINE structure of its type (and reference counts are used
+ to keep order). The dynamic ENGINE itself provides absolutely no
+ cryptographic functionality, and any attempt to "initialise" the ENGINE
+ automatically fails. All it does provide are a few "control commands"
+ that can be used to control how it will load an external ENGINE
+ implementation from a shared-library. To see these control commands,
+ use the command-line;
+
+ openssl engine -vvvv dynamic
+
+ The "SO_PATH" control command should be used to identify the
+ shared-library that contains the ENGINE implementation, and "NO_VCHECK"
+ might possibly be useful if there is a minor version conflict and you
+ (or a vendor helpdesk) is convinced you can safely ignore it.
+ "ENGINE_ID" is probably only needed if a shared-library implements
+ multiple ENGINEs, but if you know the engine id you expect to be using,
+ it doesn't hurt to specify it (and this provides a sanity check if
+ nothing else). "LIST_ADD" is only required if you actually wish the
+ loaded ENGINE to be discoverable by application code later on using the
+ ENGINE's "id". For most applications, this isn't necessary - but some
+ application authors may have nifty reasons for using it. The "LOAD"
+ command is the only one that takes no parameters and is the command
+ that uses the settings from any previous commands to actually *load*
+ the shared-library ENGINE implementation. If this command succeeds, the
+ (copy of the) 'dynamic' ENGINE will magically morph into the ENGINE
+ that has been loaded from the shared-library. As such, any control
+ commands supported by the loaded ENGINE could then be executed as per
+ normal. Eg. if ENGINE "foo" is implemented in the shared-library
+ "libfoo.so" and it supports some special control command "CMD_FOO", the
+ following code would load and use it (NB: obviously this code has no
+ error checking);
+
+ ENGINE *e = ENGINE_by_id("dynamic");
+ ENGINE_ctrl_cmd_string(e, "SO_PATH", "/lib/libfoo.so", 0);
+ ENGINE_ctrl_cmd_string(e, "ENGINE_ID", "foo", 0);
+ ENGINE_ctrl_cmd_string(e, "LOAD", NULL, 0);
+ ENGINE_ctrl_cmd_string(e, "CMD_FOO", "some input data", 0);
+
+ For testing, the "openssl engine" utility can be useful for this sort
+ of thing. For example the above code excerpt would achieve much the
+ same result as;
+
+ openssl engine dynamic \
+ -pre SO_PATH:/lib/libfoo.so \
+ -pre ENGINE_ID:foo \
+ -pre LOAD \
+ -pre "CMD_FOO:some input data"
+
+ Or to simply see the list of commands supported by the "foo" ENGINE;
+
+ openssl engine -vvvv dynamic \
+ -pre SO_PATH:/lib/libfoo.so \
+ -pre ENGINE_ID:foo \
+ -pre LOAD
+
+ Applications that support the ENGINE API and more specifically, the
+ "control commands" mechanism, will provide some way for you to pass
+ such commands through to ENGINEs. As such, you would select "dynamic"
+ as the ENGINE to use, and the parameters/commands you pass would
+ control the *actual* ENGINE used. Each command is actually a name-value
+ pair and the value can sometimes be omitted (eg. the "LOAD" command).
+ Whilst the syntax demonstrated in "openssl engine" uses a colon to
+ separate the command name from the value, applications may provide
+ their own syntax for making that separation (eg. a win32 registry
+ key-value pair may be used by some applications). The reason for the
+ "-pre" syntax in the "openssl engine" utility is that some commands
+ might be issued to an ENGINE *after* it has been initialised for use.
+ Eg. if an ENGINE implementation requires a smart-card to be inserted
+ during intialisation (or a PIN to be typed, or whatever), there may be
+ a control command you can issue afterwards to "forget" the smart-card
+ so that additional initialisation is no longer possible. In
+ applications such as web-servers, where potentially volatile code may
+ run on the same host system, this may provide some arguable security
+ value. In such a case, the command would be passed to the ENGINE after
+ it has been initialised for use, and so the "-post" switch would be
+ used instead. Applications may provide a different syntax for
+ supporting this distinction, and some may simply not provide it at all
+ ("-pre" is almost always what you're after, in reality).
+ How do I build a "dynamic" ENGINE?
+ ----------------------------------
+ This question is trickier - currently OpenSSL bundles various ENGINE
+ implementations that are statically built in, and any application that
+ calls the "ENGINE_load_builtin_engines()" function will automatically
+ have all such ENGINEs available (and occupying memory). Applications
+ that don't call that function have no ENGINEs available like that and
+ would have to use "dynamic" to load any such ENGINE - but on the other
+ hand such applications would only have the memory footprint of any
+ ENGINEs explicitly loaded using user/admin provided control commands.
+ The main advantage of not statically linking ENGINEs and only using
+ "dynamic" for hardare support is that any installation using no
+ "external" ENGINE suffers no unecessary memory footprint from unused
+ ENGINEs. Likewise, installations that do require an ENGINE incur the
+ overheads from only *that* ENGINE once it has been loaded.
- No external crypto device is chosen unless you say so. You have actively
- tell the openssl utility commands to use it through a new command line
- switch called "-engine". And if you want to use the ENGINE library to
- do something similar, you must also explicitely choose an external crypto
- device, or the built-in crypto routines will be used, just as in the
- default OpenSSL distribution.
+ Sounds good? Maybe, but currently building an ENGINE implementation as
+ a shared-library that can be loaded by "dynamic" isn't automated in
+ OpenSSL's build process. It can be done manually quite easily however.
+ Such a shared-library can either be built with any OpenSSL code it
+ needs statically linked in, or it can link dynamically against OpenSSL
+ if OpenSSL itself is built as a shared library. The instructions are
+ the same in each case, but in the former (statically linked any
+ dependencies on OpenSSL) you must ensure OpenSSL is built with
+ position-independant code ("PIC"). The default OpenSSL compilation may
+ already specify the relevant flags to do this, but you should consult
+ with your compiler documentation if you are in any doubt.
+ This example will show building the "atalla" ENGINE in the
+ crypto/engine/ directory as a shared-library for use via the "dynamic"
+ ENGINE.
+ 1) "cd" to the crypto/engine/ directory of a pre-compiled OpenSSL
+ source tree.
+ 2) Recompile at least one source file so you can see all the compiler
+ flags (and syntax) being used to build normally. Eg;
+ touch hw_atalla.c ; make
+ will rebuild "hw_atalla.o" using all such flags.
+ 3) Manually enter the same compilation line to compile the
+ "hw_atalla.c" file but with the following two changes;
+ (a) add "-DENGINE_DYNAMIC_SUPPORT" to the command line switches,
+ (b) change the output file from "hw_atalla.o" to something new,
+ eg. "tmp_atalla.o"
+ 4) Link "tmp_atalla.o" into a shared-library using the top-level
+ OpenSSL libraries to resolve any dependencies. The syntax for doing
+ this depends heavily on your system/compiler and is a nightmare
+ known well to anyone who has worked with shared-library portability
+ before. 'gcc' on Linux, for example, would use the following syntax;
+ gcc -shared -o dyn_atalla.so tmp_atalla.o -L../.. -lcrypto
+ 5) Test your shared library using "openssl engine" as explained in the
+ previous section. Eg. from the top-level directory, you might try;
+ apps/openssl engine -vvvv dynamic \
+ -pre SO_PATH:./crypto/engine/dyn_atalla.so -pre LOAD
+ If the shared-library loads successfully, you will see both "-pre"
+ commands marked as "SUCCESS" and the list of control commands
+ displayed (because of "-vvvv") will be the control commands for the
+ *atalla* ENGINE (ie. *not* the 'dynamic' ENGINE). You can also add
+ the "-t" switch to the utility if you want it to try and initialise
+ the atalla ENGINE for use to test any possible hardware/driver
+ issues.
PROBLEMS
========
- It seems like the ENGINE part doesn't work too well with Cryptoswift on
- Win32. A quick test done right before the release showed that trying
- "openssl speed -engine cswift" generated errors. If the DSO gets enabled,
- an attempt is made to write at memory address 0x00000002.
+ It seems like the ENGINE part doesn't work too well with Cryptoswift on Win32.
+ A quick test done right before the release showed that trying "openssl speed
+ -engine cswift" generated errors. If the DSO gets enabled, an attempt is made
+ to write at memory address 0x00000002.
projects / oweals / openssl.git / commitdiff