FBB::EncryptBuf(3bobcat) | Encrypt information | FBB::EncryptBuf(3bobcat) |
FBB::EncryptBuf - Encrypts information using various methods into a std::ostream
#include <bobcat/encryptbuf>
Linking option: -lbobcat -lcrypto
FBB::EncryptBuf objects are std::streambuf objects that can be used to initialize std::ostream objects.
All information inserted into such a std::ostream is encrypted and written into an std::ostream that is given as argument to EncryptBuf’s constructor.
All encryption methods supported by the OpenSSL library that can be selected by name may be used by 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).
Most modes use initialization vectors. Unless provided at construction time EncryptBuf objects create random initialization vectors. The initialization vector that is actually used can be obtained from the EncryptBuf object. This is important, as the matching decryption object needs to know the initialization vector that was used when encrypting the data. Initialization vectors are not considered confidential and 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 encryption method it is automatically extended with 0-bytes to the required length.
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.
FBB
All constructors, members, operators and manipulators, mentioned in this
man-page, are defined in the namespace FBB.
FBB::CryptBuf, in turn inheriting from std::streambuf
completes the decryption once EncryptBuf’s destructor is called. Alternatively,
endStream << inStream.rdbuf();
can be used to immediately complete the encryption process.
encStream << inStream.rdbuf() << end;
Copy and move constructors (and assignment operators) are not available.
All members of std::streambuf are available, as FBB::EncryptBuf inherits from this class.
#include <iostream> #include <iomanip> #include <fstream> #include <bobcat/exception> #include <bobcat/ohexbuf> #include "../encryptbuf" #include <openssl/evp.h> 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: (opt): iv, "
"stdin: file to encrypt (to stdout)\n"
"e.g., driver aes-128-cbc somekey < driver.cc > /tmp/enc\n";
string key(argv[2]);
string iv;
if (argc > 3)
iv = argv[3];
EncryptBuf encryptbuf(cout, argv[1], key, iv, 50);
ostream out(&encryptbuf);
size_t ivLength = encryptbuf.iv().length();
cerr << "Block length: " << encryptbuf.blockLength() << "\n"
"Key length: " << encryptbuf.keyLength() << "\n"
"Max Key length: " << EVP_MAX_KEY_LENGTH << "\n"
"actual IV length: " << ivLength << "\n"
"IV =\n";
OHexBuf ohb{ cerr, ivLength << 1 };
ostream outHex(&ohb);
outHex << encryptbuf.iv();
cerr << ’\n’ << dec;
out << cin.rdbuf() << eoi; } catch(exception const &err) {
cerr << err.what() << endl;
return 1; }
To ignore the initial 256 bytes generated by the RC4 algorithm a simple wrapper class around the eventual output stream can be used. Here is an illustration:
Next, an Skip256 object is used to define an intermediate std::ostream that is then passed to the EncryptBuf object. E.g., only showing the essential steps defining the EncryptBuf object:
#include <ostream>
#include <bobcat/ofilterbuf>
class Skip256: public FBB::OFilterBuf
{
size_t d_count;
public:
Skip256(std::ostream &os)
:
OFilterBuf(os),
d_count(0)
{}
private:
virtual int overflow(int c)
{
if (d_count == 256)
out().put(c);
else
++d_count;
return c;
}
};
Skip256 skip256(std::cout);
std::ostream out(&skip256);
EncryptBuf encryptbuf(out, "rc4", key, "");
bobcat/encryptbuf - defines the class interface
bobcat(7), decryptbuf(3bobcat), ofilterbuf(3bobcat), std::streambuf
None reported
Bobcat is an acronym of `Brokken’s Own Base Classes And Templates’.
This is free software, distributed under the terms of the GNU General Public License (GPL).
Frank B. Brokken (f.b.brokken@rug.nl).
2005-2020 | libbobcat-dev_5.07.00 |