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    1   ENGINE
    2   ======
    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.
   62   =======================
   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.
   85   USAGE
   86   =====
   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.
  114   ===============
  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
  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?
  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"
  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.
  282   PROBLEMS
  283   ========
  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.