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<h1 id="title">FBB::DecryptBuf(3bobcat)</h1>
<h2 id="author">Decrypt information<br/>(libbobcat-dev_4.08.02-x.tar.gz)</h2>
<h2 id="date">2005-2017</h2>
<p>
<h2 >NAME</h2>FBB::DecryptBuf - Decrypts information using various methods into a std::ostream
<p>
<h2 >SYNOPSIS</h2>
<strong >#include <bobcat/decryptbuf></strong><br/>
Linking option: <em > -lbobcat -lcrypto</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>
Block ciphers use one of the following four encryption modes:
<ul>
<li> <strong >CBC (Cipher Block Chaining)</strong>:<br/>
The first block is XOR-ed by the initialization vector and then
encrypted using the specified method. Subsequent blocks are XOR-ed by the
encrypted version of the preceding block. Due to the initialization vector
dictionary attacks are infeasible, as long as the initialization vector is
truly random.
<li> <strong >ECB (Electronic Code Book)</strong>:<br/>
Each block is encrypted by itself, using the specified encryption
method. Although an <em >initialization vector</em> may be specified, it is not
used. This method is susceptible to dictionary attacks and should therefore be
avoided, unless you know what you're doing.
<li> <strong >CFB (Cipher Feednack)</strong>:<br/>
This method allows a block cipher to be used as a stream cipher. It
uses an initialization vector, which should be unique and random for each new
stream of data that is encrypted using the method. Encryption can only start
after the first data block has been received.
<li> <strong >OFB (Output Feednack)</strong>:<br/>
This is an alternative way to use a block cipher as a stream
cipher. It is somewhat more susceptible to traditional data manipulation
attacks, which can usually be thwarted when a message authentication code is
added to the information as well. Like CFB it uses an initialization vector,
which should again be unique and random for each new stream of data that is
encrypted.
</ul>
<p>
The following table presents an overview of methods that are currently
available. Methods for which the block size is specified as N.A. are stream
ciphers; other methods are block ciphers:
<table>
<tr><td colspan=5><hr/></td></tr>
<tr >
<td > method</td><td > keysize</td><td > blocksize</td><td > mode</td><td > identifier</td>
</tr>
<tr >
<td > </td><td > (bytes)</td><td > (bytes)</td>
</tr>
<tr><td colspan=5><hr/></td></tr>
<tr >
<td > AES</td><td > 16</td><td > 8</td><td > CBC</td><td > "aes-128-cbc"</td>
</tr>
<tr >
<td > </td><td > </td><td > </td><td > EBC</td><td > "aes-128-ecb"</td>
</tr>
<tr >
<td > </td><td > </td><td > </td><td > CFB</td><td > "aes-128-cfb"</td>
</tr>
<tr >
<td > </td><td > </td><td > </td><td > OFB</td><td > "aes-128-ofb"</td>
</tr>
<tr >
<td > </td><td > 24</td><td > 24</td><td > CBC</td><td > "aes-192-cbc"</td>
</tr>
<tr >
<td > </td><td > </td><td > </td><td > EBC</td><td > "aes-192-ecb"</td>
</tr>
<tr >
<td > </td><td > </td><td > </td><td > CFB</td><td > "aes-192-cfb"</td>
</tr>
<tr >
<td > </td><td > </td><td > </td><td > OFB</td><td > "aes-192-ofb"</td>
</tr>
<tr >
<td > </td><td > 32</td><td > 32</td><td > CBC</td><td > "aes-256-cbc"</td>
</tr>
<tr >
<td > </td><td > </td><td > </td><td > EBC</td><td > "aes-256-ecb"</td>
</tr>
<tr >
<td > </td><td > </td><td > </td><td > CFB</td><td > "aes-256-cfb"</td>
</tr>
<tr >
<td > </td><td > </td><td > </td><td > OFB</td><td > "aes-256-ofb"</td>
</tr>
<tr><td colspan=5><hr/></td></tr>
<tr >
<td > BLOWFISH</td><td > 16</td><td > 8</td><td > CBC</td><td > "bf-cbc"</td>
</tr>
<tr >
<td > </td><td > </td><td > </td><td > EBC</td><td > "bf-ecb"</td>
</tr>
<tr >
<td > </td><td > </td><td > </td><td > CFB</td><td > "bf-cfb"</td>
</tr>
<tr >
<td > </td><td > </td><td > </td><td > OFB</td><td > "bf-ofb"</td>
</tr>
<tr >
<td > max key length is 56 bytes, 16 generally used</td>
</tr>
<tr><td colspan=5><hr/></td></tr>
<tr >
<td > CAMELLIA</td><td > 16</td><td > 16</td><td > CBC</td><td > "camellia-128-cbc"</td>
</tr>
<tr >
<td > </td><td > </td><td > </td><td > EBC</td><td > "camellia-128-ecb"</td>
</tr>
<tr >
<td > </td><td > </td><td > </td><td > CFB</td><td > "camellia-128-cfb"</td>
</tr>
<tr >
<td > </td><td > </td><td > </td><td > OFB</td><td > "camellia-128-ofb"</td>
</tr>
<tr >
<td > </td><td > 24</td><td > </td><td > CBC</td><td > "camellia-192-cbc"</td>
</tr>
<tr >
<td > </td><td > </td><td > </td><td > EBC</td><td > "camellia-192-ecb"</td>
</tr>
<tr >
<td > </td><td > </td><td > </td><td > CFB</td><td > "camellia-192-cfb"</td>
</tr>
<tr >
<td > </td><td > </td><td > </td><td > OFB</td><td > "camellia-192-ofb"</td>
</tr>
<tr >
<td > </td><td > 32</td><td > </td><td > CBC</td><td > "camellia-256-cbc"</td>
</tr>
<tr >
<td > </td><td > </td><td > </td><td > EBC</td><td > "camellia-256-ecb"</td>
</tr>
<tr >
<td > </td><td > </td><td > </td><td > CFB</td><td > "camellia-256-cfb"</td>
</tr>
<tr >
<td > </td><td > </td><td > </td><td > OFB</td><td > "camellia-256-ofb"</td>
</tr>
<tr><td colspan=5><hr/></td></tr>
<tr >
<td > CAST</td><td > 16</td><td > 8</td><td > CBC</td><td > "cast-cbc"</td>
</tr>
<tr >
<td > </td><td > </td><td > </td><td > EBC</td><td > "cast-ecb"</td>
</tr>
<tr >
<td > </td><td > </td><td > </td><td > CFB</td><td > "cast-cfb"</td>
</tr>
<tr >
<td > </td><td > </td><td > </td><td > OFB</td><td > "cast-ofb"</td>
</tr>
<tr >
<td > min key length is 5 bytes, max is shown</td>
</tr>
<tr><td colspan=5><hr/></td></tr>
<tr >
<td > DES</td><td > 8</td><td > 8</td><td > CBC</td><td > "des-cbc"</td>
</tr>
<tr >
<td > </td><td > </td><td > </td><td > EBC</td><td > "des-ebc"</td>
</tr>
<tr >
<td > </td><td > </td><td > </td><td > CFB</td><td > "des-cfb"</td>
</tr>
<tr >
<td > </td><td > </td><td > </td><td > OFB</td><td > "des-ofb"</td>
</tr>
<tr><td colspan=5><hr/></td></tr>
<tr >
<td > DESX</td><td > 8</td><td > 8</td><td > CBC</td><td > "desx-cbc"</td>
</tr>
<tr><td colspan=5><hr/></td></tr>
<tr >
<td > 3DES</td><td > 16</td><td > 8</td><td > CBC</td><td > "des-ede-cbc"</td>
</tr>
<tr >
<td > </td><td > </td><td > </td><td > EBC</td><td > "des-ede"</td>
</tr>
<tr >
<td > </td><td > </td><td > </td><td > CFB</td><td > "des-ede-cfb"</td>
</tr>
<tr >
<td > </td><td > </td><td > </td><td > OFB</td><td > "des-ede-ofb"</td>
</tr>
<tr><td colspan=5><hr/></td></tr>
<tr >
<td > 3DES</td><td > 24</td><td > 8</td><td > CBC</td><td > "des-ede3-cbc"</td>
</tr>
<tr >
<td > </td><td > </td><td > </td><td > EBC</td><td > "des-ede3"</td>
</tr>
<tr >
<td > </td><td > </td><td > </td><td > CFB</td><td > "des-ede3-cfb"</td>
</tr>
<tr >
<td > </td><td > </td><td > </td><td > OFB</td><td > "des-ede3-ofb"</td>
</tr>
<tr >
<td > Key bytes 9-16 define the 2nd key, bytes 17-24</td>
</tr>
<tr >
<td > define the 3rd key</td>
</tr>
<tr><td colspan=5><hr/></td></tr>
<tr >
<td > RC2</td><td > 16</td><td > 8</td><td > CBC</td><td > "rc2-cbc"</td>
</tr>
<tr >
<td > </td><td > </td><td > </td><td > EBC</td><td > "rc2-ecb"</td>
</tr>
<tr >
<td > </td><td > </td><td > </td><td > CFB</td><td > "rc2-cfb"</td>
</tr>
<tr >
<td > </td><td > </td><td > </td><td > OFB</td><td > "rc2-ofb"</td>
</tr>
<tr >
<td > Key length variable, max. 128 bytes, default length is shown</td>
</tr>
<tr><td colspan=5><hr/></td></tr>
<tr >
<td > RC2-40</td><td > 5</td><td > 8</td><td > </td><td > "rc2-40-cbc"</td>
</tr>
<tr >
<td > obsolete: avoid</td>
</tr>
<tr><td colspan=5><hr/></td></tr>
<tr >
<td > RC2-64</td><td > 8</td><td > 8</td><td > </td><td > "rc2-64-cbc"</td>
</tr>
<tr >
<td > obsolete: avoid</td>
</tr>
<tr><td colspan=5><hr/></td></tr>
<tr >
<td > RC4</td><td > 16</td><td > N.A.</td><td > </td><td > "rc4"</td>
</tr>
<tr >
<td > Key length is variable, max. 256 bytes. default length is shown</td>
</tr>
<tr >
<td > Encrypt again to decrypt. Don't use <em >DecryptBuf</em></td>
</tr>
<tr><td colspan=5><hr/></td></tr>
<tr >
<td > RC4-40</td><td > 5</td><td > N.A.</td><td > </td><td > "rc4-40"</td>
</tr>
<tr >
<td > obsolete: avoid</td>
</tr>
<tr><td colspan=5><hr/></td></tr>
<tr >
<td > RC5</td><td > 16</td><td > 8</td><td > CBC</td><td > "rc5-cbc"</td>
</tr>
<tr >
<td > </td><td > </td><td > </td><td > EBC</td><td > "rc5-ecb"</td>
</tr>
<tr >
<td > </td><td > </td><td > </td><td > CFB</td><td > "rc5-cfb"</td>
</tr>
<tr >
<td > </td><td > </td><td > </td><td > OFB</td><td > "rc5-ofb"</td>
</tr>
<tr >
<td > Key length variable, max. 256 bytes, rounds 8, 12 or 16,</td>
</tr>
<tr >
<td > default # rounds is 12</td>
</tr>
<tr><td colspan=5><hr/></td></tr>
</table>
<p>
The RC4 stream cipher is subject to a well-known attack
(cf. <a href="http://www.wisdom.weizmann.ac.il/~itsik/RC4/Papers/Mantin1.zip">http://www.wisdom.weizmann.ac.il/~itsik/RC4/Papers/Mantin1.zip</a>)
unless the initial 256 bytes produced by the cipher are discarded.
<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 &outStream, char const *type,
std::string const &key, std::string const &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::Exception</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::Exception</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 &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 initialization vector
an <em >FBB::Exception</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 <iostream>
#include <fstream>
#include <bobcat/exception>
#include <bobcat/decryptbuf>
using namespace std;
using namespace FBB;
int main(int argc, char **argv)
try
{
if (argc == 1)
throw Exception(1) <<
"1st arg: method, 2nd arg: key, 3rd arg: file to "
"decrypt (to stdout), 4th arg: iv";
cerr << "Key: `" << argv[2] << "'\n"
"IV: `" << argv[4] << "'\n";
DecryptBuf decryptbuf(cout, argv[1], argv[2], argv[4]);
ostream out(&decryptbuf);
ifstream in(argv[3]);
out << in.rdbuf();
}
catch(exception const &err)
{
cout << err.what() << 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_4.08.02-x.dsc</em>: detached signature;
<li> <em >bobcat_4.08.02-x.tar.gz</em>: source archive;
<li> <em >bobcat_4.08.02-x_i386.changes</em>: change log;
<li> <em >libbobcat1_4.08.02-x_*.deb</em>: debian package holding the
libraries;
<li> <em >libbobcat1-dev_4.08.02-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>
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