---
name: "isymcryptstreambuf"
section: "3bobcat"
platform: "linux"
package: "libbobcat-dev"
version: "6.07.01-2"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/isymcryptstreambuf"
---

# isymcryptstreambuf(3bobcat)

Streambuf performing symmetric en/decryption

## NAME

FBB::ISymCryptStreambuf - Streambuf performing symmetric en/decryption

## SYNOPSIS

**#include \<bobcat/isymcryptstreambuf\>**\
 Linking option: *-lbobcat -lcrypto*

## DESCRIPTION

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

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.

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
```

*ISymCryptStreambuf* objects read the information to en/decrypt from *std::istream* objects, which are at construction-time specified as *istream* references or by filename. The characters that are thereupon extracted or read from *ISymCryptStream* objects are en/decrypted, and could, e.g., be written to some output stream.

## NAMESPACE

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

## INHERITS FROM

**FBB::ISymCryptBase** (public)

The class *FBB::ISymCryptBase* is an \`internal use only’ class, derived from *std::streambuf*, and therefore *ISymCryptStreambuf* is a *std::streambuf* class.

## CONSTRUCTORS

- o

  **ISymCryptStreambuf\<CryptType\>(std::istream &inStream,** **std::string const &cipherName,** **std::string const &key,** **std::string const &iv,** **size\_t inBufSize = 100)**:\
   This constructor defines a *std::streambuf* object encrypting or decrypting the characters which are read from *inStream*.

-

  \- *ISymCryptStreambuf\<FBB::ENCRYPT\>* objects perform encryption;\
   *ISymCryptStreambuf\<FBB::DECRYPT\>* objects perform decryption;

-

  \- *ISymCryptStreambuf\<CryptType\>* objects receive the characters to encrypt or decrypt from *std::istream &in*;\
   \- 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::ISymCryptStreambufbuf* internally used buffer will hold *inBufSize* characters. The default value is the smallest value that is used. When specifying a smaller *bufSize* value than the default value then the default value is used;\

-

  - o

  **ISymCryptStreambuf\<CryptType\>(std::string const &inStreamName,** **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 containing the characters to encrypt or decrypt.

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::istreambuf**, all *std::streambuf* members can can be used.

## MEMBER FUNCTIONS

- o

  **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;

-

  - o

  **static size\_t keyLength(std::string const &cipherName)**:\
   returns the minimum key length required for cipher *cipherName*;

-

  - o

  **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.

## EXAMPLE

See the example in the [**isymcryptstream**(3bobcat)](/isymcryptstream/3bobcat.md) man-page. Instead of defining an *ISymCryptStream* an *ISymCryptStreamBuf* can be defined, passing its address to a *std::istream* which can then be used as the *ISymCryptStream* used in the example.

## FILES

*bobcat/isymcryptstream* - defines the class interface

## SEE ALSO

[**bobcat**(7)](/bobcat/7.md), [**isymcryptstream**(3bobcat)](/isymcryptstream/3bobcat.md), [**osymcryptstream**(3bobcat)](/osymcryptstream/3bobcat.md), [**osymcryptstreambuf**(3bobcat)](/osymcryptstreambuf/3bobcat.md)

## BUGS

None Reported.

## BOBCAT PROJECT FILES

- o

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

Debian Bobcat project files:

- o

  *libbobcat6*: debian package containing the shared library, changelog and copyright note;

- o

  *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**).