Provided by: libbobcat-dev_5.02.00-1build1_amd64 
NAME
FBB::HMacBuf - Computes HMAC Message Digests from information inserted into a std::ostream
SYNOPSIS
#include <bobcat/hmacbuf>
Linking option: -lbobcat -lcrypto
DESCRIPTION
FBB::HMacBuf objects are std::streambuf objects that can be used to initialize std::ostream objects with.
All information inserted into such a std::ostream is used to compute a message HMAC from.
All the message digest algorithms defined by the OpenSSL library that can be selected by name may be used
in combination with HMacBuf objects.
The following message hmac algorithms are currently supported: mull, md2, md5, sha, sha1, sha224, sha256,
sha384, sha512, dss, dss1, ecdsa, mdc2, ripemd160. These very names are the ones to use to select the
particular digest algorithm for the class’s constructor, below. It is quite possible that future releases
of the openssl library will support additional message digest algorithms. The header file openssl/evp.h
lists all available hmac algorithms (in that file look for EVP_MD *EVP_: a message digest algorithm
immediately follows the 2nd underscore. E.g., const EVP_MD *EVP_md4(void) which refers to the md4 message
digest algorithm).
NAMESPACE
FBB
All constructors, members, operators and manipulators, mentioned in this man-page, are defined in the
namespace FBB.
INHERITS FROM
std::streambuf
CONSTRUCTORS
o HMacBuf(std::string const &key, char const *type, size_t bufsize = 1024):
This constructor initializes the streambuf, setting it up for the message digest algorithm
specified with type. The message hmac algorithms specified in the DESCRIPTION section may be used
here. E.g., to use the sha256 algorithm specify "sha256".
The constructor’s first argument defines the key to be used when computing the HMAC message
digest.
The bufsize argument specifies the internal buffer used by HMacBuf to store incoming characters
temporarily. The provided default argument should be OK in all normal cases.
Copy and move constructors (and assignment operators) are not available.
OVERLOADED OPERATOR
o std::ostream &operator<<(std::ostream &out, HMacBuf const &hmacbuf):
The insertion operator is a free function defined in the namespace FBB. It inserts a hash value as
a series of hexadecimally displayed values into the provided ostream. See the example below for an
illustration.
MEMBER FUNCTIONS
All members of std::streambuf are available, as FBB::HMacBuf inherits from this class.
o void eoi():
This member completes the message digest computation. It is needed as the HMacBuf object has no
external means for deciding whether all information to compute the digest for has yet been
received or not. Alternatively, the eoi manipulator can be inserted into the stream computing the
message digest (see below) The general approach for computing a message hmac is therefore:
create a HMacBuf object
use it to create a std::ostream object
insert information into the ostream object
call the HMacBuf object’s eoi() member or insert eoi into the ostream
object
obtain/process the hash value from the HMacBuf object.
o std::string const &hash() const:
This member returns the hash value computed by the HMacBuf object. Its value is only defined after
having called close(). The hash value is returned in a std::string object. This string’s length()
member contains the number of characters used by the hash value, and its data() member refers to
the hash value’s characters. Note that a hash value’s character value may be 0 (not to be confused
with ’0’).
o void reset():
This member reinitializes the message hmac computation. One a message hmac has been computed for,
say a stream streamA this member can be called after which the hmac for a stream streamB can be
computed using the same HMacBuf object.
o void eoi():
This member can be called to complete the message digest computation. Instead of calling this
member the eoi manipulator (see below) can be used.
MANIPULATOR
o FBB::eoi:
The eoi manipulator can be inserted into the ostream to complete the digest computation. If it is
inserted into a plain std::ostream nothing happens.
EXAMPLE
#include <iostream>
#include <ostream>
#include <cstring>
#include <iomanip>
#include <bobcat/exception>
#include "../hmacbuf"
using namespace std;
using namespace FBB;
int main(int argc, char **argv)
try
{
if (argc < 3)
throw Exception{} << "Arg1: key, arg2: digest method required";
string key(argv[1]);
HMacBuf hmacbuf{ key, argv[2] };
ostream out(&hmacbuf);
string hw{ "hello world\n" };
out << hw << eoi;
cout << ">" << hmacbuf << "<" << endl;
// hmacbuf.reset();
// out.write(hw.c_str(), hw.length()) << eoi;
// cout << ">" << hmacbuf << "<" << endl;
}
catch(exception const &err)
{
cout << err.what() << endl;
return errno;
}
FILES
bobcat/hmacbuf - defines the class interface
SEE ALSO
bobcat(7), digestbuf(3bobcat), std::streambuf
BUGS
None reported
DISTRIBUTION FILES
o bobcat_5.02.00-x.dsc: detached signature;
o bobcat_5.02.00-x.tar.gz: source archive;
o bobcat_5.02.00-x_i386.changes: change log;
o libbobcat1_5.02.00-x_*.deb: debian package holding the libraries;
o libbobcat1-dev_5.02.00-x_*.deb: debian package holding the libraries, headers and manual pages;
o http://sourceforge.net/projects/bobcat: public archive location;
BOBCAT
Bobcat is an acronym of `Brokken’s Own Base Classes And Templates’.
COPYRIGHT
This is free software, distributed under the terms of the GNU General Public License (GPL).
AUTHOR
Frank B. Brokken (f.b.brokken@rug.nl).