FBB::DecryptBuf(3bobcat)

Decrypt information
(libbobcat-dev_4.08.03-x.tar.gz)

2005-2018

NAME

FBB::DecryptBuf - Decrypts information using various methods into a std::ostream

SYNOPSIS

#include <bobcat/decryptbuf>
Linking option: -lbobcat -lcrypto

DESCRIPTION

FBB::DecryptBuf objects are std::streambuf objects that can be used to initialize std::ostream objects with.

All information inserted into such a std::ostream is decrypted and written into a std::ostream that is given as argument to DecryptBuf's constructor.

All encryption methods defined by the OpenSSL library that can be selected by name may be used in combination with DecryptBuf objects. Most likely the information will have been encrypted using an EncryptBuf object, selecting a particular encryption method. The encryption method used when encrypting information should also be specified when constructing a DecryptBuf object. Likewise, the constructor expects a key and initialization vector. The key and initialization vector that was passed to the EncryptBuf object must be passed to DecryptBuf's constructor as well.

Block ciphers use one of the following four encryption modes:

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:


method keysize blocksize mode identifier
(bytes) (bytes)

AES 16 8 CBC "aes-128-cbc"
EBC "aes-128-ecb"
CFB "aes-128-cfb"
OFB "aes-128-ofb"
24 24 CBC "aes-192-cbc"
EBC "aes-192-ecb"
CFB "aes-192-cfb"
OFB "aes-192-ofb"
32 32 CBC "aes-256-cbc"
EBC "aes-256-ecb"
CFB "aes-256-cfb"
OFB "aes-256-ofb"

BLOWFISH 16 8 CBC "bf-cbc"
EBC "bf-ecb"
CFB "bf-cfb"
OFB "bf-ofb"
max key length is 56 bytes, 16 generally used

CAMELLIA 16 16 CBC "camellia-128-cbc"
EBC "camellia-128-ecb"
CFB "camellia-128-cfb"
OFB "camellia-128-ofb"
24 CBC "camellia-192-cbc"
EBC "camellia-192-ecb"
CFB "camellia-192-cfb"
OFB "camellia-192-ofb"
32 CBC "camellia-256-cbc"
EBC "camellia-256-ecb"
CFB "camellia-256-cfb"
OFB "camellia-256-ofb"

CAST 16 8 CBC "cast-cbc"
EBC "cast-ecb"
CFB "cast-cfb"
OFB "cast-ofb"
min key length is 5 bytes, max is shown

DES 8 8 CBC "des-cbc"
EBC "des-ebc"
CFB "des-cfb"
OFB "des-ofb"

DESX 8 8 CBC "desx-cbc"

3DES 16 8 CBC "des-ede-cbc"
EBC "des-ede"
CFB "des-ede-cfb"
OFB "des-ede-ofb"

3DES 24 8 CBC "des-ede3-cbc"
EBC "des-ede3"
CFB "des-ede3-cfb"
OFB "des-ede3-ofb"
Key bytes 9-16 define the 2nd key, bytes 17-24
define the 3rd key

RC2 16 8 CBC "rc2-cbc"
EBC "rc2-ecb"
CFB "rc2-cfb"
OFB "rc2-ofb"
Key length variable, max. 128 bytes, default length is shown

RC2-40 5 8 "rc2-40-cbc"
obsolete: avoid

RC2-64 8 8 "rc2-64-cbc"
obsolete: avoid

RC4 16 N.A. "rc4"
Key length is variable, max. 256 bytes. default length is shown
Encrypt again to decrypt. Don't use DecryptBuf

RC4-40 5 N.A. "rc4-40"
obsolete: avoid

RC5 16 8 CBC "rc5-cbc"
EBC "rc5-ecb"
CFB "rc5-cfb"
OFB "rc5-ofb"
Key length variable, max. 256 bytes, rounds 8, 12 or 16,
default # rounds is 12

The RC4 stream cipher is subject to a well-known attack (cf. http://www.wisdom.weizmann.ac.il/~itsik/RC4/Papers/Mantin1.zip) unless the initial 256 bytes produced by the cipher are discarded.

NAMESPACE

FBB
All constructors, members, operators and manipulators, mentioned in this man-page, are defined in the namespace FBB.

INHERITS FROM

std::streambuf

CONSTRUCTOR/DESTRUCTOR

There is no copy constructor, nor move constructor (as std::streambuf doesn't support either).

MEMBER FUNCTIONS

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

STATIC MEMBER

PROTECTED MEMBER

EXAMPLE

#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;
}





FILES

bobcat/decryptbuf - defines the class interface

SEE ALSO

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

BUGS

None reported

DISTRIBUTION FILES

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).