FBB::Digestbuf(3bobcat) 				      Compute Message Digests					   FBB::Digestbuf(3bobcat)

NAME

       FBB::Digestbuf - Computes Message Digests from information inserted into a std::ostream

SYNOPSIS

       #include <bobcat/digestbuf>
       Linking option: -lbobcat

DESCRIPTION

       FBB::Digestbuf 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 digest from.

       All the message digests defined by the OpenSSL library that can be selected by name may be used in combination with DigestBuf objects.

       The  following  message	digest	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 algorithms 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 digest 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      Digestbuf(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 digest
	      algorithms specified in the DESCRIPTION section may be used here. E.g., to use the sha256 algorithm specify "sha256".

	      The bufsize argument specifies the internal buffer used by Digestbuf to store incoming characters temporarily. The provided  default
	      argument should be OK in all normal cases.  There is no copy constructor.

OVERLOADED OPERATOR

       o      std::ostream &operator<<(std::ostream &out, DigestBuf const &digestbuf):
	      The  insertion  operator	is a free function defined in the namespace FBB. It inserts a hash value as a series of hexadecimally dis-
	      played values into the provided ostream. See the example below for an illustration.   The  overloaded  assignment  operator  is  not
	      available.

MEMBER FUNCTIONS

       All members of std::streambuf are available, as FBB::Digestbuf inherits from this class. Some of the std::streambuf's member are overridden
       or are hidden by Digestbuf. In normal situations these inherited members will not be used by programs using DigestBuf objects.

       o      void close():
	      This member finishes the computation of the  message digest computation. It is needed as the DigestBuf object has no external  means
	      for  deciding  whether  all  information to compute the digest for has yet been received or not. The general approach to follow when
	      computing a message digest is therefore:

		  create a DigestBuf object
		  use it to create a std::ostream object
		  insert information into the ostream object
		  call the DigestBuf object's close() member
		  obtain/process the hash value from the DigestBuf object.

       o      std::string const &hash() const:
	      This member returns the hash value computed by the DigestBuf 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 open():
	      This member reinitializes the message digest computation. One a message digest has been computed for, say a stream streamA this mem-
	      ber can be called after which the digest for a stream streamB can be computed using the same DigestBuf object.

EXAMPLE

       #include <iostream>
       #include <ostream>
       #include <bobcat/errno>
       #include <bobcat/digestbuf>

       using namespace std;
       using namespace FBB;

       int main(int argc, char **argv)
       try
       {
	   DigestBuf digestbuf(argv[1]);
	   ostream out(&digestbuf);

	   string hw("hello world
");

	   out << hw;
	   digestbuf.close();
	   cout << ">" << digestbuf << "<" << endl;

	   digestbuf.open();
	   out.write(hw.c_str(), hw.length());
	   digestbuf.close();
	   cout << ">" << digestbuf << "<" << endl;
       }
       catch(Errno const &err)
       {
	   cout << err.why() << endl;
	   return 1;
       }

FILES

       bobcat/digestbuf - defines the class interface

SEE ALSO

       bobcat(7), hmacbuf(3bobcat), std::streambuf

BUGS

       None reported

DISTRIBUTION FILES

       o      bobcat_3.01.00-x.dsc: detached signature;

       o      bobcat_3.01.00-x.tar.gz: source archive;

       o      bobcat_3.01.00-x_i386.changes: change log;

       o      libbobcat1_3.01.00-x_*.deb: debian package holding the libraries;

       o      libbobcat1-dev_3.01.00-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).

libbobcat1-dev_3.01.00-x.tar.gz 				     2005-2012						   FBB::Digestbuf(3bobcat)