/usr/share/doc/libbobcat2-dev/man/decryptbuf.3.html

<html><head>
<title>FBB::DecryptBuf</title>
<link rev="made" href="mailto:Frank B. Brokken: f.b.brokken@rug.nl">
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<body text="#27408B" bgcolor="#FFFAF0">
<hr>
<h1>FBB::DecryptBuf</h1>
<h2>libbobcat1-dev_2.20.01-x.tar.gz</h2>
<h2>2005-2011</h2>

<html><head>
<link rev="made" href="mailto:Frank B. Brokken: f.b.brokken@rug.nl">
</head>
<body text="#27408B" bgcolor="#FFFAF0">
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<h1></h1>

<html><head>
<title>FBB::DecryptBuf(3bobcat)</title>
<link rev="made" href="mailto:Frank B. Brokken: f.b.brokken@rug.nl">
</head>
<body text="#27408B" bgcolor="#FFFAF0">
<hr>
<h1>FBB::DecryptBuf(3bobcat)</h1>
<h2>libbobcat1-dev_2.20.01-x.tar.gz Decrypt information</h2>
<h2>2005-2011</h2>


<p>
<h2>NAME</h2>FBB::DecryptBuf - Decrypts information using various methods into a std::ostream 
<p>
<h2>SYNOPSIS</h2>
    <strong>#include &lt;bobcat/decryptbuf&gt;</strong><br>
    Linking option: <em> -lbobcat</em> 
<p>
<h2>DESCRIPTION</h2>
    <strong>FBB::DecryptBuf</strong> objects are <strong>std::streambuf</strong> objects that can be used
to initialize <em>std::ostream</em> objects with.
<p>
All information inserted into such a <em>std::ostream</em> is decrypted and
written into a <em>std::ostream</em> that is given as argument to <em>DecryptBuf</em>'s
constructor.
<p>
All encryption methods defined by the OpenSSL library that can be selected
by name may be used in combination with <em>DecryptBuf</em> objects. Most likely
the information will have been encrypted using an <em>EncryptBuf</em> object,
selecting a particular encryption method. The encryption method used when
encrypting information should also be specified when constructing a
<em>DecryptBuf</em> object. Likewise, the constructor expects a <em>key</em> and
<em>initialization vector</em>. The key and initialization vector that was passed
to the <em>EncryptBuf</em> object must be passed to <em>DecryptBuf</em>'s constructor as
well. 
<p>
Information about the various encryption methods and cipher modes as well
as information about how keys and initialization vectors are handled is found
in the <strong>EncryptBuf</strong>(3bobcat) manual page and need not be repeated here.
<p>
<h2>NAMESPACE</h2>
    <strong>FBB</strong><br>
    All constructors, members, operators and manipulators, mentioned in this
man-page, are defined in the namespace <strong>FBB</strong>.
<p>
<h2>INHERITS FROM</h2>
    <strong>std::streambuf</strong>
<p>
<h2>CONSTRUCTOR/DESTRUCTOR</h2>
    <ul>
    <li> <strong>DecryptBuf(std::ostream &amp;outStream, char const *type, 
                            std::string const &amp;key, std::string const &amp;iv,
                            size_t bufsize = 1024)</strong>:<br>
        This constructor initializes the <em>DecryptBuf</em> object preparing it
for the message decrypt algorithm specified with <em>type</em>. The decryption
algorithms that can be used are listed in the table found in the
<strong>EncryptBuf</strong>(3bobcat) manual page. As an example: to use the AES method on
192 bit keys and blocks in CBC mode specify <em>"aes-192-cbc"</em>. The <em>key</em>
parameter refers to the key to be used, the <em>iv</em> parameter refers to the
initialization vector to use. The <em>iv</em>'s length cannot be zero. When using 
ECB modes no initialization vector is used. In those cases any non-empty
initialization vector may be provided.
<p>
The constructor throws an <em>FBB::Errno</em> exception if an unknown
encryption method was specified.
<p>
The constructor's first parameter refers to the <em>std::ostream</em> to
receive the decrypted information.
<p>
The <em>bufsize</em> argument specifies the size in bytes of the internal
buffer used by <em>DecryptBuf</em> to store incoming characters temporarily. The
provided default argument should be OK in all normal cases.
    <li> <strong>~DecryptBuf()</strong>:<br> 
        The destructor calls the <em>done()</em> member (see below), prevending any
exception that function might throw from leaving the destructor. In this case
only a non thread-safe way to determine whether the decryption was
successfully completed is available through the static member function
<em>lastOK()</em> (see below).
    </ul>
    There is no copy constructor, nor move constructor (as <em>std::streambuf</em>
doesn't support either).
<p>
<h2>MEMBER FUNCTIONS</h2>
<p>
All members of <strong>std::streambuf</strong> are available, as <strong>FBB::DecryptBuf</strong>
inherits from this class. Some of the <strong>std::streambuf</strong>'s member are
overridden or are hidden by <em>DecryptBuf</em>. In normal situations these
inherited members will not be used by programs using <em>DecryptBuf</em> objects.
<p>
<ul>
    <li> <strong>void done()</strong>:<br>
        This member can be called to indicate that all information to be
decrypted has been received. It throws an <em>FBB::Errno</em> exception if
decryption fails (resulting from providing the <em>DecryptBuf</em> object with
incorrect (usually improperly padded) input). If not explicitly called it is
called by <em>DecryptBuf</em>'s destructor, preventing its exception from leaving
the destructor. 
    <li> <strong>void setIv(std::string const &amp;iv)</strong>:<br>
        This member can be used to specify the initialization vector to use
after construction time but before any data has been decrypted. When called
after decryption has started or when specifying an empty intialization vector
an <em>FBB::Errno</em> exception will be thrown.  When using ECB modes no
initialization vector is used. In those cases any non-empty initialization
vector may be provided.
    <li> <strong>bool setRounds(size_t nRounds)</strong>:<br>
        This member can only be used with the RC5 decryption method to set the
number of rounds of the algorithm to 8, 12 or 16. When the number of rounds
were updated successfully the member returns <em>true</em>. It returns <em>false</em> in
other cases (e.g., called for other decryption methods than RC5 or the
requested number of rounds differ from 8, 12 or 16).
    </ul>
<p>
<h2>STATIC MEMBER</h2>
    <ul>
    <li> <strong>bool lastOK()</strong>:<br>
        This member is a non thread-safe way to determine whether the
decryption has succeeded when the  <em>DecryptBuf</em> object's <em>done</em> member has
not been called and the object has been destroyed. In that case the object's
destructor will call <em>done</em> to complete the decryption. The member
<em>lastOK</em> returns <em>true</em> if the <em>DecryptBuf</em> object  destroyed last
could complete its decryption successfully and returns <em>false</em> otherwise. 
    </ul>
<p>
<h2>PROTECTED MEMBER</h2>
    <ul>
    <li> <strong>EVP_CIPHER_CTX *cipherCtx()</strong>:<br>
        Classes derived from <em>DecryptBuf</em> may use this member to gain direct
access to the <em>EVP_CIPHER_CTX</em> pointer used by the <em>DecryptBuf</em>
object. This pointer is a pointer to an opaque structure used by many OpenSSL
functions to set or query parameters of an decryption method.
    </ul>
<p>
<h2>EXAMPLE</h2>
    <pre>
#include &lt;iostream&gt;
#include &lt;fstream&gt;
#include &lt;bobcat/errno&gt;
#include &lt;bobcat/decryptbuf&gt;

using namespace std;
using namespace FBB;

int main(int argc, char **argv)
try
{
    if (argc == 1)
        throw Errno("1st arg: method, 2nd arg: key, 3rd arg: file to "
                    "decrypt (to stdout), 4th arg: iv");

    cerr &lt;&lt; "Key: `" &lt;&lt; argv[2] &lt;&lt; "'\n"
            "IV:  `" &lt;&lt; argv[4] &lt;&lt; "'\n";

    DecryptBuf decryptbuf(cout, argv[1], argv[2], argv[4]);
    ostream out(&amp;decryptbuf);
    ifstream in(argv[3]);

    out &lt;&lt; in.rdbuf();
    // decryptbuf.done();       // optionally
}
catch(Errno const &amp;err)
{
    cout &lt;&lt; err.why() &lt;&lt; endl;
    return 1;
}





</pre>

<p>
<h2>FILES</h2>
    <em>bobcat/decryptbuf</em> - defines the class interface
<p>
<h2>SEE ALSO</h2>
    <strong>bobcat</strong>(7), <strong>encryptbuf</strong>(3bobcat), <strong>std::streambuf</strong>
<p>
<h2>BUGS</h2>
    None reported
<p>

<h2>DISTRIBUTION FILES</h2>
    <ul>
    <li> <em>bobcat_2.20.01-x.dsc</em>: detached signature;
    <li> <em>bobcat_2.20.01-x.tar.gz</em>: source archive;
    <li> <em>bobcat_2.20.01-x_i386.changes</em>: change log;
    <li> <em>libbobcat1_2.20.01-x_*.deb</em>: debian package holding the
            libraries;
    <li> <em>libbobcat1-dev_2.20.01-x_*.deb</em>: debian package holding the
            libraries, headers and manual pages;
    <li> <em>http://sourceforge.net/projects/bobcat</em>: public archive location;
    </ul>
<p>
<h2>BOBCAT</h2>
    Bobcat is an acronym of `Brokken's Own Base Classes And Templates'.
<p>
<h2>COPYRIGHT</h2>
    This is free software, distributed under the terms of the 
    GNU General Public License (GPL).
<p>
<h2>AUTHOR</h2>
    Frank B. Brokken (<strong>f.b.brokken@rug.nl</strong>).
<p>
libbobcat-dev 2.20.01-1 / usr / share / doc / libbobcat2-dev / man / decryptbuf.3.html
