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The Low-Level Interface
=================================
Botan has two different interfaces. The one documented in this section
is meant more for implementing higher-level types (see the section on
filters, earlier in this manual) than for use by applications. Using
it safely requires a solid knowledge of encryption techniques and best
practices, so unless you know, for example, what CBC mode and nonces
are, and why PKCS #1 padding is important, you should avoid this
interface in favor of something working at a higher level.
Basic Algorithm Abilities
---------------------------------
There are a small handful of functions implemented by most of Botan's
algorithm objects. Among these are:
.. cpp:function:: std::string name()
Returns a human-readable string of the name of this
algorithm. Examples of names returned are "AES-128" and
"HMAC(SHA-512)". You can turn names back into algorithm objects using
the functions in ``lookup.h``.
.. cpp:function:: void clear()
Clear out the algorithm's internal state. A block cipher object will
"forget" its key, a hash function will "forget" any data put into it,
etc. The object will look and behave as it did when you initially
allocated it.
.. cpp:function:: T* clone()
The ``clone`` has many different return types, such as
``BlockCipher``\* and ``HashFunction``\*, depending on what kind of
object it is called on. Note that unlike Java's clone, this returns a
new object in a "pristine" state; that is, operations done on the
initial object before calling ``clone`` do not affect the initial
state of the new clone.
Cloned objects can (and should) be deallocated with the C++ ``delete``
operator.
Keys and IVs
---------------------------------
Both symmetric keys and initialization values can be considered byte
(or octet) strings. These are represented by
.. cpp:class:: OctetString
Also known as ``SymmetricKey`` and ``InitializationVector``, when
you want to express intent.
.. cpp:function:: OctetString(RandomNumberGenerator& rng, size_t length)
This constructor creates a new random key *length* bytes long
using the random number generator.
.. cpp:function:: OctetString(std::string str)
The argument *str* is assumed to be a hex string; it is
converted to binary and stored. Whitespace is ignored.
.. cpp:function:: OctetString(const byte* input, size_t length)
This constructor copies its input.
.. cpp:function:: as_string() const
Returns the hex representation of the key or IV
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