readme.engine

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  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 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

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