# FBB::OSymCryptStreambuf(3bobcat)

## Symmetric en- and decryption
(libbobcat-dev_6.14.00)

## 2005-2026

## NAME

FBB::OSymCryptStreambuf - std::streambuf performing symmetric en/decryption

## SYNOPSIS

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

## DESCRIPTION

FBB::OSymCryptStreambuf objects can be used as std::streambuf objects of std::ostream objects, and encrypt or decrypt information, that is made available via separate std::istream streams.

The class OSymCryptStreambuf is a class template, using a FBB::CryptType template non-type parameter. Objects of the class FBB::OSymCryptStreambuf<FBB::ENCRYPT> encrypt the information they receive, objects of the class FBB::OSymCryptStreambuf<FBB::DECRYPT> decrypt the information they receive.

All symmetric encryption methods defined by the OpenSSL library that can be selected by name may be used to en/decrypt information. To select a particular encryption method an identifier is passed to the constructor. E.g., "aes-256-gcm". For an overview of the currently supported cipher algorithms issue the command

        openssl list -cipher-algorithms

OSymCryptStreambuf objects read the information to en/decrypt from an external source (e.g., from std::istream objects). The characters that are encrypted or decrypted by OSymCryptStreambuf objects are written to std::ostream objects which are at construction-time specified as ostream references or by filename.

## NAMESPACE

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

## INHERITS FROM

FBB::OSymCryptBase (public)

The class FBB::OSymCryptBase is an `internal use only' class, derived from std::streambuf, and therefore OSymCryptStreambuf is a std::streambuf class.

## CONSTRUCTORS

- OSymCryptStreambuf<CryptType>(std::ostream &outStreambuf, std::string const &cipherName, std::string const &key, std::string const &iv, size_t inBufSize = 100):
  This constructor defines a std::streambuf encrypting or decrypting the characters it receives.

  - OSymCryptStreambuf<FBB::ENCRYPT> objects perform encryption;
  OSymCryptStreambuf<FBB::DECRYPT> objects perform decryption;

  - OSymCryptStreambuf<CryptType> objects write the encrypted or decrypted characters to outStreambuf;
  - The encryption method to use is specified by the cipherName parameter. E.g., "AES-256-GCM";
  - The symmetric key to use is specified by the key parameter;
  - The initialization vector is specified by the iv parameter;
  - The FBB::OSymCryptStreambufbuf internally used buffer will hold inBufSize characters. The default value is the smallest value that is used. When specifying a smaller bufSize value the default value is used;

- OSymCryptStreambuf<CryptType>(std::string const &outStreambufName, std::string const &cipherName, std::string const &key, std::string const &iv, size_t inBufSize = 100):
  Same constructor as the previous one, but this constructor's first parameter specifies the name of the file to receive the encrypted or decrypted characters.

If the construction fails an exception is thrown, mentioning the openssl function that failed to complete (see also errorMsg below).

The move constructor is available, the copy constructor and assignment operators are not available,

## INHERITED MEMBERS

Since the class is publicly derived from std::ostream, all std::streambuf members can be used.

## MEMBER FUNCTIONS

- static std::string errorMsg():
  If an openssl function fails an exception is thrown mentioning the name of the failing function. In those cases the function errorMsg can be called returning a std::string containing the openssl error code (returned by ERR_get_error) and its textual representation (returned by ERR_error_string). If the reported error code is zero, then in fact no error has occurred and the exception was spuriously reported;

- static size_t keyLength(std::string const &cipherName):
  returns the minimum key length required for cipher cipherName;

- static size_t ivLength(std::sting const &cipherName):
  returns the minimum length of the initialization vector that is required for cipher cipherName.

The latter two functions throw exceptions if cipherName does not contain the name of a supported cipher algorithm.

## MANIPULATOR

- std::ostream &FBB::eoi(std::ostream &out):
  By inserting the eoi manipulator into an std::ostream object that uses a OSymCryptStreambuf streambuf insertion is considered complete. It completes the insertion of information into the std::ostream specified at construction time as the OSymCryptStreambuf's first argument. That way, you don't have to wait until the OSymCryptStreambuf object's destructor flushes that stream. The example provided at the osymcryptstream(3bobcat) man-page illustrates the use of the eoi manipulator.

## EXAMPLE

See the example in the osymcryptstream(3bobcat) man-page. Instead of defining an OSymCryptStream an OSymCryptStreamBuf can be defined, passing its address to a std::ostream which can then be used as the OSymCryptStream used in the example.

## FILES

bobcat/osymcryptstreambuf - defines the class interface

## SEE ALSO

bobcat(7), isymcryptstream(3bobcat), isymcryptstreambuf(3bobcat), osymcryptstream(3bobcat)

## BUGS

None Reported.

## BOBCAT PROJECT FILES

- https://fbb-git.gitlab.io/bobcat/: gitlab project page;

Debian Bobcat project files:

- libbobcat6: debian package containing the shared library, changelog and copyright note;
- libbobcat-dev: debian package containing the static library, headers, manual pages, and developer info;

## 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).