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209 lines
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209 lines
9.0 KiB
Plaintext
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Frequently Asked Questions
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========================================
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What is this thing?
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----------------------------------------
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Botan is a library written in C++ which provides a fairly high level
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and C++-ish interface to a number of different crypto algorithms. In
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addition to the bare algorithms there is also support for number of
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standards and de-facto standards like X.509v3 certificates, and
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various useful constructs like format-preserving encryption, all or
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nothing transforms, and secret splitting.
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.. _devel_vs_stable:
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Which release should I use?
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----------------------------------------
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The library is normally released along two different trees, termed
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stable and development. The stable tree is a branch off the main line,
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and typically only sees bug fixes; almost all new development occurs
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in the unstable/development releases. The primary issue is not
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stability of the program (bugs of course do occur, and are more likely
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to occur in code that is more in flux), but rather stability of API
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and ABI. In particular, you should not expect any level of ABI
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stability between releases on the development branch, and API changes
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may be made without notice. Feel free to send comments on API changes,
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or API problems, to the list.
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If you don't want to have to worry about tracking a moving target, and
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just want something that works, you'll probably prefer using the
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stable releases. If you want to get the latest features, the
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development releases are the obvious choice.
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If you want to ship a binary that is usable out of the box on a Linux
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distro that ships botan, you'll probably want to match versions with
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that distro; as of this writing most ship with 1.8.
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If you're building an application that will embed botan into it
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(without relying on a shared library), you want to use an amalgamation
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build, which basically turns botan into a single header and a single
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source file which you can easily include in your existing application
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build. In this case you can pick which ever tree you prefer.
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The self-test program can't locate the library
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-----------------------------------------------
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Are you sure either the current working directory ('.') or the
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directory botan is building into are in the dynamic library path? On
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many Unix systems this is controlled by the ``LD_LIBRARY_PATH``
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variable. You can add the currently directory to the list of
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directories to search with this Bourne shell command::
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$ export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:.
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If you install the library into a well known location like
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``/usr/local/lib``, then probably no particular
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``LD_LIBRARY_PATH`` needs to be set.
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My program aborts with any message
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----------------------------------------
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Does your main function wrap all code inside a try/catch block? If an
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exception is thrown and is not caught, many C++ runtimes simply crash
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the process without providing any sort of diagnostic.
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Is the library thread-safe?
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----------------------------------------
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Yes, botan is thread safe. However, because mutual exclusion depends
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on OS specific code, you must load a module to help. POSIX threads and
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Win32 critical sections are both supported out of the box, other
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thread libraries are very easy to add. To enable thread safe
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operation, include "thread_safe" in the string you pass to
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``Botan::LibraryInitializer`` constructor. If for whatever reason a
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working mutex implementation cannot be found, LibraryInitializer will
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throw an exception rather than continue operating in a bad state.
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How do I load this key generated by OpenSSL into botan?
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--------------------------------------------------------
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The encrypted key format used by the ``openssl`` command line tool is
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undocumented and apparently specific to OpenSSL. The easiest approach
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is to convert it to the (standard) PKCS #8 format, using::
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openssl pkcs8 -topk8 -in my_key.pem
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Add ``-nocrypt`` to the command line if you want the resulting PKCS #8
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file to be unencrypted, otherwise it will ask you for a new password
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to use.
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For unencrypted keys, you can also manually decode the parameters
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using the existing PEM and BER support; see `this post
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<http://lists.randombit.net/pipermail/botan-devel/2010-June/001156.html>`_
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to the dev list for an example.
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Is botan FIPS 140 certified?
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----------------------------------------
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No version of botan has been certified under FIPS 140. This is
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unlikely to happen unless/until an organization is willing to fund and
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shepherd the validation process, which typically requires several
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months and many thousands of dollars.
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Is this thing safe to use?
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----------------------------------------
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The primary author/maintainer (Jack Lloyd) has 5+ years of experience
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reviewing code for security flaws, and has additionally performed
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several FIPS 140 validations of hardware and software crypto
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implementations. However the library has never undergone an
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*impartial* third-party security review, and thus it is entirely
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possible/probable that a number of exploitable flaws remain in the
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source. (If your company is interested in handling such a review,
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please contact the maintainers).
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There has been one known security flaw. Between versions 0.7.8
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(released Feb 2002) and 1.3.7 (released Dec 2003), the ``es_unix``
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module, which runs Unix programs to gather entropy for seeding a
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random number generator, ran programs by invoking the ``popen``
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library function with commands with no leading directory names. This
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means setuid or setgid programs that used this entropy source could be
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tricked into executing arbitrary programs via manipulation of the PATH
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variable. Later versions will only search through specific (presumed
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safe) directories like ``/usr/bin``; the list of directories to search
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can be controlled by the application.
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Is botan vulnerable to timing attacks?
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----------------------------------------
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Botan's public key implementations do make some attempt to defend
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against timing attacks; random blinding is used to protect all RSA,
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Rabin-Williams, ElGamal, and Diffie-Hellman private key operations.
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Public key algorithms implemented using the Chinese Remainder Theorem
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(RSA and Rabin-Williams) are subject to a catastrophic failure: if a
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computational error (either induced by an attacker or merely
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accidental) occurs during the private key operation, the private key
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can be revealed. Other, more subtle, fault attacks are possible against
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other schemes. For this reason, private key operations are checked
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for consistency with the public key - if the results are not
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consistent, then an exception is thrown indicating an error has
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occurred rather than release information that might compromise the
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key.
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AES implementations are usually quite vulnerable to timing attacks.
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The table based implementation of AES included in botan uses small
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tables in the first and last rounds which makes such attacks somewhat
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more difficult. Alternate implementations of AES using SSSE3 and
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AES-NI instruction sets are also included, and run in constant time,
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but of course require a processor that supports these instruction
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sets.
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I think I've found a security flaw. What should I do?
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------------------------------------------------------------
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You can do any combination of:
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* Contact the current lead maintainer personally; currently
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`Jack Lloyd <http://www.randombit.net>`_
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(`personal PGP key <http://www.randombit.net/pgpgkey.html>`_)
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* Email the `development list
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<http://lists.randombit.net/mailman/listinfo/botan-devel>`_
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* File a bug in `Bugzilla <http://bugs.randombit.net/>`_
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Does botan support SSL/TLS, SSH, S/MIME, OpenPGP...
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------------------------------------------------------------
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Support for SSL/TLS is included in version 1.9.4 and later. Currently
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SSLv3 and TLS 1.0 and 1.1 are supported.
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`NetSieben SSH <http://netsieben.com/products/ssh/>`_ is an open
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source SSHv2 implementation that uses botan.
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A preliminary and very incomplete implementation of CMS (the crypto
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layer underlying S/MIME) is included in ``src/cms``, but it needs a
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lot of love and attention before being truly useful.
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There is currently no support for OpenPGP.
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Will it work on my platform XYZ??
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----------------------------------------
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The most common stumbling block is a compiler that is buggy or can't
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handle modern C++ (specifically, C++98). Check out the :doc:`build log
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<build_log>` for a sense of which platforms are actively being tested.
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I'm not feeling this, what can I use instead?
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------------------------------------------------------------
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* `Crypto++ <http://www.cryptopp.com/>`_ is another C++ crypto
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library. Its API is more heavily based on templates and in general
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has a very different design philosophy from botan - so if you feel
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botan's API is not a good match, you may well like Crypto++.
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* `OpenSSL <http://www.openssl.org>`_ is written in C and mostly
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targeted to being an SSL/TLS implementation but there is a lot of
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other stuff in there as well.
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* `XySSL <http://www.ohloh.net/projects/xyssl>`_ is a C library
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providing a very small footprint crypto library and SSL
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implementation.
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* `Adam Shostack <http://www.homeport.org/~adam/crypto/>`_ maintains a
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(somewhat out of date) list of open source crypto libraries.
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