StreamTransformation Class Referenceabstract

Interface for the data processing portion of stream ciphers. More...

Inheritance diagram for StreamTransformation:

## Public Member Functions

StreamTransformation & | Ref ()
| Provides a reference to this object. More...
virtual unsigned int | MandatoryBlockSize () const
| Provides the mandatory block size of the cipher. More...
virtual unsigned int | OptimalBlockSize () const
| Provides the input block size most efficient for this cipher. More...
virtual unsigned int | GetOptimalBlockSizeUsed () const
| Provides the number of bytes used in the current block when processing at optimal block size. More...
virtual unsigned int | OptimalDataAlignment () const
| Provides input and output data alignment for optimal performance. More...
virtual void | ProcessData (byte *outString, const byte *inString, size_t length)=0
| Encrypt or decrypt an array of bytes. More...
virtual size_t | ProcessLastBlock (byte *outString, size_t outLength, const byte *inString, size_t inLength)
| Encrypt or decrypt the last block of data. More...
virtual unsigned int | MinLastBlockSize () const
| Provides the size of the last block. More...
virtual bool | IsLastBlockSpecial () const
| Determines if the last block receives special processing. More...
void | ProcessString (byte *inoutString, size_t length)
| Encrypt or decrypt a string of bytes. More...
void | ProcessString (byte *outString, const byte *inString, size_t length)
| Encrypt or decrypt a string of bytes. More...
byte | ProcessByte (byte input)
| Encrypt or decrypt a byte. More...
virtual bool | IsRandomAccess () const =0
| Determines whether the cipher supports random access. More...
virtual void | Seek (lword pos)
| Seek to an absolute position. More...
virtual bool | IsSelfInverting () const =0
| Determines whether the cipher is self-inverting. More...
virtual bool | IsForwardTransformation () const =0
| Determines if the cipher is being operated in its forward direction. More...
Public Member Functions inherited from Algorithm
| Algorithm (bool checkSelfTestStatus=true)
| Interface for all crypto algorithms. More...
virtual std::string | AlgorithmName () const
| Provides the name of this algorithm. More...
virtual std::string | AlgorithmProvider () const
| Retrieve the provider of this algorithm. More...
Public Member Functions inherited from Clonable
virtual Clonable * | Clone () const
| Copies this object. More...

## Detailed Description

Interface for the data processing portion of stream ciphers.

See also
  StreamTransformationFilter()

Definition at line 945 of file cryptlib.h.

## Member Function Documentation

## Ref()

StreamTransformation& StreamTransformation::Ref | ( |  | ) |

inline

Provides a reference to this object.

Returns
  A reference to this object

Useful for passing a temporary object to a function that takes a non-const reference

Definition at line 953 of file cryptlib.h.

## MandatoryBlockSize()

virtual unsigned int StreamTransformation::MandatoryBlockSize | ( |  | ) | const

inline virtual

Provides the mandatory block size of the cipher.

Returns
  The block size of the cipher if input must be processed in blocks, 1 otherwise

Stream ciphers and some block ciphers modes of operation return 1. Modes that return 1 must be able to process a single byte at a time, like counter mode. If a mode of operation or block cipher cannot stream then it must not return 1.

When filters operate the mode or cipher, ProcessData will be called with a string of bytes that is determined by MandatoryBlockSize and OptimalBlockSize. When a policy is set, like 16-byte strings for a 16-byte block cipher, the filter will buffer bytes until the specified number of bytes is available to the object.

See also
  ProcessData, ProcessLastBlock, MandatoryBlockSize, MinLastBlockSize, BlockPaddingSchemeDef, IsLastBlockSpecial

Reimplemented in BlockOrientedCipherModeBase.

Definition at line 965 of file cryptlib.h.

## OptimalBlockSize()

virtual unsigned int StreamTransformation::OptimalBlockSize | ( |  | ) | const

inline virtual

Provides the input block size most efficient for this cipher.

Returns
  The input block size that is most efficient for the cipher

The base class implementation returns MandatoryBlockSize().

Note
  Optimal input length is `n * OptimalBlockSize() - GetOptimalBlockSizeUsed()` for any `n > 0`.

Reimplemented in AdditiveCipherTemplate< BASE >, and ECB_OneWay.

Definition at line 972 of file cryptlib.h.

## GetOptimalBlockSizeUsed()

virtual unsigned int StreamTransformation::GetOptimalBlockSizeUsed | ( |  | ) | const

inline virtual

Provides the number of bytes used in the current block when processing at optimal block size.

Returns
  the number of bytes used in the current block when processing at the optimal block size

Definition at line 976 of file cryptlib.h.

## OptimalDataAlignment()

virtual unsigned int StreamTransformation::OptimalDataAlignment | ( |  | ) | const

virtual

Provides input and output data alignment for optimal performance.

Returns
  the input data alignment that provides optimal performance

See also
  GetAlignment() and OptimalBlockSize()

Reimplemented in XTS_ModeBase, AdditiveCipherTemplate< BASE >, CipherModeBase, GCM_Base, EAX_Base, XChaCha20Poly1305_Base, ChaCha20Poly1305_Base, and CCM_Base.

## ProcessData()

virtual void StreamTransformation::ProcessData | ( | byte * | outString,
|  | const byte * | inString,
|  | size_t | length
| ) |  |

pure virtual

Encrypt or decrypt an array of bytes.

Parameters

  outString | the output byte buffer
  inString | the input byte buffer
  length | the size of the input and output byte buffers, in bytes

ProcessData is called with a string of bytes whose size depends on MandatoryBlockSize. Either `inString == outString`, or they must not overlap.

See also
  ProcessData, ProcessLastBlock, MandatoryBlockSize, MinLastBlockSize, BlockPaddingSchemeDef, IsLastBlockSpecial

Implemented in XTS_ModeBase, AdditiveCipherTemplate< BASE >, CBC_Decryption, CBC_Encryption, ECB_OneWay, PublicBlumBlumShub, AuthenticatedSymmetricCipherBase, and Weak::ARC4_Base.

## ProcessLastBlock()

virtual size_t StreamTransformation::ProcessLastBlock | ( | byte * | outString,
|  | size_t | outLength,
|  | const byte * | inString,
|  | size_t | inLength
| ) |  |

virtual

Encrypt or decrypt the last block of data.

Parameters

  outString | the output byte buffer
  outLength | the size of the output byte buffer, in bytes
  inString | the input byte buffer
  inLength | the size of the input byte buffer, in bytes

Returns
  the number of bytes used in outString

ProcessLastBlock is used when the last block of data is special and requires handling by the cipher. The current implementation provides an output buffer with a size `inLength+2*MandatoryBlockSize()`. The return value allows the cipher to expand cipher text during encryption or shrink plain text during decryption.

This member function is used by CBC-CTS and OCB modes.

See also
  ProcessData, ProcessLastBlock, MandatoryBlockSize, MinLastBlockSize, BlockPaddingSchemeDef, IsLastBlockSpecial

Reimplemented in XTS_ModeBase, CBC_CTS_Decryption, and CBC_CTS_Encryption.

## MinLastBlockSize()

virtual unsigned int StreamTransformation::MinLastBlockSize | ( |  | ) | const

inline virtual

Provides the size of the last block.

Returns
  the minimum size of the last block

MinLastBlockSize() returns the minimum size of the last block. 0 indicates the last block is not special.

MandatoryBlockSize() enlists one of two behaviors. First, if MandatoryBlockSize() returns 1, then the cipher can be streamed and ProcessData() is called with the tail bytes. Second, if MandatoryBlockSize() returns non-0, then the string of bytes is padded to MandatoryBlockSize() according to the padding mode. Then, ProcessData() is called with the padded string of bytes.

Some authenticated encryption modes are not expressed well with MandatoryBlockSize() and MinLastBlockSize(). For example, AES/OCB uses 16-byte blocks (MandatoryBlockSize = 16) and the last block requires special processing (MinLastBlockSize = 0). However, 0 is a valid last block size for OCB and the special processing is custom padding, and not standard PKCS padding. In response an unambiguous IsLastBlockSpecial() was added.

See also
  ProcessData, ProcessLastBlock, MandatoryBlockSize, MinLastBlockSize, BlockPaddingSchemeDef, IsLastBlockSpecial

Reimplemented in XTS_ModeBase, CBC_CTS_Decryption, CBC_CTS_Encryption, and CBC_ModeBase.

Definition at line 1021 of file cryptlib.h.

## IsLastBlockSpecial()

virtual bool StreamTransformation::IsLastBlockSpecial | ( |  | ) | const

inline virtual

Determines if the last block receives special processing.

Returns
  true if the last block reveives special processing, false otherwise.

Some authenticated encryption modes are not expressed well with MandatoryBlockSize() and MinLastBlockSize(). For example, AES/OCB uses 16-byte blocks (MandatoryBlockSize = 16) and the last block requires special processing (MinLastBlockSize = 0). However, 0 is a valid last block size for OCB and the special processing is custom padding, and not standard PKCS padding. In response an unambiguous IsLastBlockSpecial() was added.

When IsLastBlockSpecial() returns false nothing special happens. All the former rules and behaviors apply. This is the default behavior of IsLastBlockSpecial().

When IsLastBlockSpecial() returns true four things happen. First, MinLastBlockSize = 0 means 0 is a valid block size that should be processed. Second, standard block cipher padding is not applied. Third, the caller supplies an outString is larger than inString by `2*MandatoryBlockSize()`. That is, there's a reserve available when processing the last block. Fourth, the cipher is responsible for finalization like custom padding. The cipher will tell the library how many bytes were processed or used by returning the appropriate value from ProcessLastBlock().

The return value of ProcessLastBlock() indicates how many bytes were written to `outString`. A filter pipelining data will send `outString` and up to `outLength` to an `AttachedTransformation()` for additional processing. Below is an example of the code used in `StreamTransformationFilter::LastPut`.

      if (m_cipher.IsLastBlockSpecial())
      {
        size_t reserve = 2*m_cipher.MandatoryBlockSize();
        space = HelpCreatePutSpace(*AttachedTransformation(), DEFAULT_CHANNEL, length+reserve);
        length = m_cipher.ProcessLastBlock(space, length+reserve, inString, length);
        AttachedTransformation()->Put(space, length);
        return;
      }

See also
  ProcessData, ProcessLastBlock, MandatoryBlockSize, MinLastBlockSize, BlockPaddingSchemeDef, IsLastBlockSpecial

Since
  Crypto++ 6.0

Definition at line 1054 of file cryptlib.h.

## ProcessString() [1/2]

void StreamTransformation::ProcessString | ( | byte * | inoutString,
|  | size_t | length
| ) |  |

inline

Encrypt or decrypt a string of bytes.

Parameters

  inoutString | the string to process
  length | the size of the inoutString, in bytes

Internally, the base class implementation calls ProcessData().

Definition at line 1060 of file cryptlib.h.

## ProcessString() [2/2]

void StreamTransformation::ProcessString | ( | byte * | outString,
|  | const byte * | inString,
|  | size_t | length
| ) |  |

inline

Encrypt or decrypt a string of bytes.

Parameters

  outString | the output string to process
  inString | the input string to process
  length | the size of the input and output strings, in bytes

Internally, the base class implementation calls ProcessData().

Definition at line 1068 of file cryptlib.h.

## ProcessByte()

byte StreamTransformation::ProcessByte | ( | byte | input | ) |

inline

Encrypt or decrypt a byte.

Parameters

  input | the input byte to process

Internally, the base class implementation calls ProcessData() with a size of 1.

Definition at line 1074 of file cryptlib.h.

## IsRandomAccess()

virtual bool StreamTransformation::IsRandomAccess | ( |  | ) | const

pure virtual

Determines whether the cipher supports random access.

Returns
  true if the cipher supports random access, false otherwise

Implemented in AdditiveCipherTemplate< BASE >, BlockOrientedCipherModeBase, BlumBlumShub, AuthenticatedSymmetricCipherBase, and Weak::ARC4_Base.

## Seek()

virtual void StreamTransformation::Seek | ( | lword | pos | ) |

inline virtual

Seek to an absolute position.

Parameters

  pos | position to seek

Exceptions

  NotImplemented |

The base class implementation throws NotImplemented. The function asserts IsRandomAccess() in debug builds.

Reimplemented in AdditiveCipherTemplate< BASE >, and BlumBlumShub.

Definition at line 1086 of file cryptlib.h.

## IsSelfInverting()

virtual bool StreamTransformation::IsSelfInverting | ( |  | ) | const

pure virtual

Determines whether the cipher is self-inverting.

Returns
  true if the cipher is self-inverting, false otherwise

IsSelfInverting determines whether this transformation is self-inverting (e.g. xor with a keystream).

Implemented in AdditiveCipherTemplate< BASE >, BlockOrientedCipherModeBase, PublicBlumBlumShub, AuthenticatedSymmetricCipherBase, and Weak::ARC4_Base.

## IsForwardTransformation()

virtual bool StreamTransformation::IsForwardTransformation | ( |  | ) | const

pure virtual

Determines if the cipher is being operated in its forward direction.

Returns
  true if DIR is ENCRYPTION, false otherwise

See also
  IsForwardTransformation(), IsPermutation(), GetCipherDirection()

Implemented in AdditiveCipherTemplate< BASE >, BlockOrientedCipherModeBase, GCM_Final< T_BlockCipher, T_TablesOption, T_IsEncryption >, EAX_Final< T_BlockCipher, T_IsEncryption >, CCM_Final< T_BlockCipher, T_DefaultDigestSize, T_IsEncryption >, PublicBlumBlumShub, and Weak::ARC4_Base.

The documentation for this class was generated from the following file:

- cryptlib.h