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_3.23.01-x.dsc: detached signature;
- o
- bobcat_3.23.01-x.tar.gz: source archive;
- o
- bobcat_3.23.01-x_i386.changes: change log;
- o
- libbobcat1_3.23.01-x_*.deb: debian package holding the
libraries;
- o
- libbobcat1-dev_3.23.01-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).