Provided by: libbobcat-dev_3.19.01-1ubuntu1_amd64 
NAME
FBB::ISymCryptStreambuf - Input Filtering stream buffer doing symmetric encryption
SYNOPSIS
#include <bobcat/isymcryptstreambuf>
Linking option: -lbobcat -lcrypto
DESCRIPTION
The information made available by ISymCryptStreambuf objects has been subject to symmetric
encryption or decryption. The information to be encrypted or decrypted is made available
to ISymCryptStreambuf object via std::istream objects.
The class ISymCryptStreambuf is a class template, using a FBB::CryptType template non-type
parameter. Objects of the class FBB::ISymCryptStreambuf<FBB::ENCRYPT> encrypt the
information they receive, objects of the class FBB::ISymCryptStreambuf<FBB::DECRYPT>
decrypt the information they receive. See also section ENUMERATION below.
All symmetric encryption methods defined by the OpenSSL library that can be selected by
name may be used in combination with EncryptBuf objects. To select a particular encryption
method an identifier is passed to the constructor. E.g., "aes-128-cbc" indicating the AES
(Rijndael) method, using 128 bit sized keys and blocks using `cbc’ mode (see below for an
explanation).
When providing shorter keys than expected by the method the provided key is extended by
adding the required number of 0-bytes. (zero valued bytes, not ’0’ characters).
Most modes use an initialization vector. The initialization vector must be provided at
construction time. The matching decrypting object needs to know the initialization vector
that was used when encrypting the data: the application must ensure that the matching
decryption object receives the same initialization vector as the one that was provided to
the encryption object. Initialization vectors are not security sensitive in the sense that
they can be sent in the clear to the decryption object. What is important, though, is that
they contain random data when used `for real’. When an initialization vector is specified
that is shorter than expected by the method it will be extended with the required number
of 0-bytes.
Block ciphers use one of the following four encryption modes:
o CBC (Cipher Block Chaining):
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.
o ECB (Electronic Code Book):
Each block is encrypted by itself, using the specified encryption method. Although
an initialization vector 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.
o CFB (Cipher Feednack):
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.
o OFB (Output Feednack):
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.
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
FBB::IFilterStreambuf
MEMBER FUNCTIONS
All members of FBB::IFilterStreambuf are available, as ISymCryptStreambuf inherits from
this class.
Overloaded move and/or copy assignment operators are not available.
ENUMERATION
ISymCryptStreambuf objects either encrypt or decrypt information. ISymCryptStreambuf
objects of the class FBB::ISymCryptStreambuf<FBB::ENCRYPT> encrypt the data they receive,
ISymCryptStreambuf objects of the class FBB::ISymCryptStreambuf<FBB::DECRYPT> decrypt the
data they receive.
The values ENCRYPT and DECRYPT are defined in the enum CryptType, which is defined in the
FBB namespace.
CONSTRUCTOR
o ISymCryptStreambuf<CryptType>( std::istream &in, char const *type,
std::string const &key, std::string const &iv, size_t bufSize = 100, size_t
filterBufSize = 1000, ENGINE *engine = 0):
This constructor initializes the streambuf. - ISymCryptStreambuf<ENCRYPT> objects
perform encryption;
ISymCryptStreambuf<DECRYPT> objects perform decryption;
- ISymCryptStreambuf<CryptType> objects obtain the bytes to encrypt or decrypt from
std::istream ∈
- The encryption method to use is specified by the type parameter. E.g., "bf-cbc"
selects the Blowfish Cipher Block Chaining method;
- The symmetric key to use is specified by the key parameter;
- The initialization vector is specified by the iv parameter;
- The FBB::ISymCryptStreambuf internally used buffer will contain bufSize
characters. The default value is the smallest value that is used. When a smaller
bufSize value is specified, the default value is used;
- FBB::ISymCryptStreambuf’s IFilterStreambuf base class is initialized with a
buffer of size filterBufSize, using a lower bound of 100;
- The parameter ENGINE can be used to specify a hardware accelleration engine, as
supported by the used encryption/decryption method. Its default argument value
indicates that no hardware accelleration is available. Copy- and move constructors
are not available.
EXAMPLE
The example shows the construction of an ISymCryptStreambuf<ENCRYPT> object ebuf which is
used to initialize a std::istream object. The information read from this istream is
encrypted using the Blowfish CBC method. A ISymCryptStreambuf<DECRYPT> object (dbuf reads
the information from that stream and decrypts it again. The std::istream din object is
initialized with the ISymCryptStreambuf<DECRYPT> object, and its contents is sent to
std::cout. The information that is presented at std::cin and that appears at std::cout
should be identical.
#include <iostream>
#include <bobcat/isymcryptstreambuf>
using namespace std;
using namespace FBB;
int main()
{
ISymCryptStreambuf<ENCRYPT> ebuf(cin, "bf-cbc",
"1234567890", "1234567890");
istream ein(&ebuf);
ISymCryptStreambuf<DECRYPT> dbuf(ein, "bf-cbc",
"1234567890", "1234567890");
istream din(&dbuf);
cout << din.rdbuf();
}
FILES
bobcat/isymcryptstreambuf - defines the class interface
SEE ALSO
bobcat(7), encryptbuf(3bobcat), isymcryptstream(3bobcat), ibase64streambuf(3bobcat),
ifilterstreambuf(3bobcat), ofilterstreambuf(3bobcat), std::streambuf.
BUGS
Sep/Oct 2013: due to a change in library handling by the linker (cf.
http://fedoraproject.org/wiki/UnderstandingDSOLinkChange and
https://wiki.debian.org/ToolChain/DSOLinking) libraries that are indirectly required are
no longer automatically linked to your program. With BigInt this is libcrypto, which
requires programs to link to both bobcat and crypto.
DISTRIBUTION FILES
o bobcat_3.19.01-x.dsc: detached signature;
o bobcat_3.19.01-x.tar.gz: source archive;
o bobcat_3.19.01-x_i386.changes: change log;
o libbobcat1_3.19.01-x_*.deb: debian package holding the libraries;
o libbobcat1-dev_3.19.01-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).