1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
|
Introduction
=================================
Botan is a C++ library that attempts to provide the most common
cryptographic algorithms and operations in an easy to use, efficient,
and portable way. It runs on a wide variety of systems, and can be
used with most modern C++ compilers.
It is released under the 2 clause BSD license and can be used by
commercial and open source software; see :ref:`license` for the
specifics.
The base library is written in ISO C++, so it can be ported with
minimal fuss, but a modules system is also used. This system exposes
system dependent code to the library through portable interfaces,
extending the set of services available to users.
The primary system targets are 32 and 64 bit CPUs, with a flat memory
address space of at least 32 bits. Given the choice between optimizing
for 32 bit systems and 64 bit systems, 64 bit is preferred, on the
general theory that where performance is a real concern, modern 64 bit
processors are the obvious choice. Smaller devices like handhelds,
settop boxes, and smart phones are also capable of using Botan.
The design makes it quite easy to remove unused algorithms in such a
way that applications do not need to be recompiled to work, even
applications that use the algorithm in question. They can ask the
library if the algorithm exists, and if so, retrieve an object
implementing that algorithm.
Recommended Reading
---------------------------------
It's a very good idea if you have some knowledge of cryptography
*before* trying to use the library. This is an area where it is very
easy to make mistakes, and where things are often subtle and/or
counterintuitive. Obviously the library tries to provide things at
a high level precisely to minimize the number of ways things can go
wrong, but naive use will almost certainly not result in a secure
system.
Especially recommended are:
- *Cryptography Engineering*
Niels Ferguson, Bruce Schneier, and Tadayoshi Kohno
- *Security Engineering -- A Guide to Building Dependable Distributed Systems*
Ross Anderson
- *Handbook of Applied Cryptography* Alfred J. Menezes, Paul C. Van
Oorschot, and Scott A. Vanstone (available online at
http://www.cacr.math.uwaterloo.ca/hac/)
Getting Help
----------------------------------------
Questions or problems you have with Botan can be directed to the
`development mailing list
<http://lists.randombit.net/mailman/listinfo/botan-devel/>`_.
"Philosophical" bug reports, announcements of programs using Botan,
and anything else having to do with Botan are also welcome.
If you find what you believe to be a bug, please file a ticket in
`Bugzilla <http://bugs.randombit.net/>`_.
A useful reference while reading this manual is the `Doxygen
documentation <http://botan.randombit.net/doxygen>`_.
Getting Started
---------------------------------
All declarations in the library are contained within the namespace
``Botan``, so you need to either prefix types with ``Botan::`` or add
a ``using`` declaration in your code. All examples will assume a
``using`` declaration.
All library headers are included like so::
#include <botan/botan.h>
Initializing the Library
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
There is a set of core services that the library needs access to while
it is performing requests. To ensure these are set up, you must create
a ``LibraryInitializer`` object (usually called 'init' in Botan
example code; 'botan\_library' or 'botan\_init' may make more sense in
real applications) prior to making any calls to Botan. This object's
lifetime must exceed that of all other Botan objects your application
creates; for this reason the best place to create the
``LibraryInitializer`` is at the start of your ``main``
function, since this guarantees that it will be created first and
destroyed last (via standard C++ RAII rules). The initializer does
things like setting up the memory allocation system and algorithm
lookup tables, finding out if there is a high resolution timer
available to use, and similar such matters. With no arguments, the
library is initialized with various default settings. So (unless you
are writing threaded code; see below), all you need is::
Botan::LibraryInitializer init;
at the start of your ``main``.
The constructor takes an optional string that specifies arguments.
Currently the only possible argument is "thread_safe", which must have
an boolean argument (for instance "thread_safe=false" or
"thread_safe=true"). If "thread_safe" is specified as true the library
will attempt to register a mutex type to properly guard access to
shared resources. However these locks do not protect individual Botan
objects: explicit locking must be used if you wish to share a single
object between threads.
If you do not create a ``LibraryInitializer`` object, all library
operations will fail, because it will be unable to do basic things
like allocate memory or get random bits. You should never create more
than one ``LibraryInitializer``.
Pitfalls
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
There are a few things to watch out for to prevent problems when using
the library.
Never allocate any kind of Botan object globally. The problem with
doing this is that the constructor for such an object will be called
before the library is initialized. Many Botan objects will, in their
constructor, make one or more calls into the library global state
object. Access to this object is checked, so an exception should be
thrown (rather than a memory access violation or undetected
uninitialized object access). A rough equivalent that will work is to
keep a global pointer to the object, initializing it after creating
your ``LibraryInitializer``. Merely making the
``LibraryInitializer`` also global will probably not help, because
C++ does not make very strong guarantees about the order that such
objects will be created.
The same rule applies for making sure the destructors of all your
Botan objects are called before the ``LibraryInitializer`` is
destroyed. This implies you can't have static variables that are Botan
objects inside functions or classes; in many C++ runtimes, these
objects will be destroyed after main has returned.
The memory object classes (``MemoryRegion``, ``MemoryVector``,
``SecureVector``) are extremely primitive, and meant only for
secure storage of potentially sensitive data like keys. They do not
meet the requirements for an STL container object and you should not
try to use them with STL algorithms. For a general-purpose container,
use ``std::vector``.
Use a ``try``/``catch`` block inside your ``main`` function, and catch
any ``std::exception`` throws (remember to catch by reference, as
``std::exception::what`` is polymorphic)::
int main()
{
try
{
LibraryInitializer init;
// ...
}
catch(std::exception& e)
{
std::cerr << e.what() << "\n";
}
}
This is not strictly required, but if you don't, and Botan throws an
exception, the runtime will call ``std::terminate``, which usually
calls ``abort`` or something like it, leaving you (or worse, a user of
your application) wondering what went wrong.
|
