+++ /dev/null
- ENGINE
- ======
-
- 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" version. 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 are currently built-in ENGINE implementations for the following
- crypto devices:
-
- o Microsoft CryptoAPI
- o VIA Padlock
- o nCipher CHIL
-
- 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
-
-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.
-
- 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. 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
- independent 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.
- "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, "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 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 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 initialisation (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 hardware support is that any installation using no
- "external" ENGINE suffers no unnecessary memory footprint from unused
- ENGINEs. Likewise, installations that do require an ENGINE incur the
- overheads from only *that* ENGINE once it has been loaded.
-
- 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-independent 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.
-
projects / openssl.git / blobdiff