bionic (3) isymcryptstreambuf.3bobcat.gz
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 acceleration engine, as supported by the
used encryption/decryption method. Its default argument value indicates that no hardware
acceleration 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_4.08.02-x.dsc: detached signature;
o bobcat_4.08.02-x.tar.gz: source archive;
o bobcat_4.08.02-x_i386.changes: change log;
o libbobcat1_4.08.02-x_*.deb: debian package holding the libraries;
o libbobcat1-dev_4.08.02-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).