OpenPGPCFBBlockCipher (Bouncy Castle Library 1.85 API Specification)
Date: 2026-07-12

org.bouncycastle.crypto.modes

## Class OpenPGPCFBBlockCipher

- java.lang.Object
- - org.bouncycastle.crypto.modes.OpenPGPCFBBlockCipher

- All Implemented Interfaces:
    BlockCipher

      public class OpenPGPCFBBlockCipher
      extends java.lang.Object
      implements BlockCipher

  Implements OpenPGP's rather strange version of Cipher-FeedBack (CFB) mode on top of a simple cipher. This class assumes the IV has been prepended to the data stream already, and just accomodates the reset after (blockSize + 2) bytes have been read.

  For further info see RFC 2440.

- - ### Constructor Summary

    Constructors
    Constructor and Description
    `OpenPGPCFBBlockCipher(BlockCipher cipher)` Basic constructor.

  - ### Method Summary

    All Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `java.lang.String` | `getAlgorithmName()` return the algorithm name and mode.
    `int` | `getBlockSize()` return the block size we are operating at.
    `BlockCipher` | `getUnderlyingCipher()` return the underlying block cipher that we are wrapping.
    `void` | `init(boolean forEncryption, CipherParameters params)` Initialise the cipher and, possibly, the initialisation vector (IV).
    `int` | `processBlock(byte[] in, int inOff, byte[] out, int outOff)` Process one block of input from the array in and write it to the out array.
    `void` | `reset()` reset the chaining vector back to the IV and reset the underlying cipher.

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- - ### Constructor Detail

    - #### OpenPGPCFBBlockCipher

          public OpenPGPCFBBlockCipher(BlockCipher cipher)

      Basic constructor.
      Parameters:
        `cipher` - the block cipher to be used as the basis of the feedback mode.

  - ### Method Detail

    - #### getUnderlyingCipher

          public BlockCipher getUnderlyingCipher()

      return the underlying block cipher that we are wrapping.
      Returns:
        the underlying block cipher that we are wrapping.

    - #### getAlgorithmName

          public java.lang.String getAlgorithmName()

      return the algorithm name and mode.
      Specified by:
        `getAlgorithmName` in interface `BlockCipher`
      Returns:
        the name of the underlying algorithm followed by "/OpenPGPCFB" and the block size in bits.

    - #### getBlockSize

          public int getBlockSize()

      return the block size we are operating at.
      Specified by:
        `getBlockSize` in interface `BlockCipher`
      Returns:
        the block size we are operating at (in bytes).

    - #### processBlock

          public int processBlock(byte[] in,
                                  int inOff,
                                  byte[] out,
                                  int outOff)
                           throws DataLengthException,
                                  java.lang.IllegalStateException

      Process one block of input from the array in and write it to the out array.
      Specified by:
        `processBlock` in interface `BlockCipher`
      Parameters:
        `in` - the array containing the input data.
        `inOff` - offset into the in array the data starts at.
        `out` - the array the output data will be copied into.
        `outOff` - the offset into the out array the output will start at.
      Returns:
        the number of bytes processed and produced.
      Throws:
        `DataLengthException` - if there isn't enough data in in, or space in out.
        `java.lang.IllegalStateException` - if the cipher isn't initialised.

    - #### reset

          public void reset()

      reset the chaining vector back to the IV and reset the underlying cipher.
      Specified by:
        `reset` in interface `BlockCipher`

    - #### init

          public void init(boolean forEncryption,
                           CipherParameters params)
                    throws java.lang.IllegalArgumentException

      Initialise the cipher and, possibly, the initialisation vector (IV). If an IV isn't passed as part of the parameter, the IV will be all zeros. An IV which is too short is handled in FIPS compliant fashion.
      Specified by:
        `init` in interface `BlockCipher`
      Parameters:
        `forEncryption` - if true the cipher is initialised for encryption, if false for decryption.
        `params` - the key and other data required by the cipher.
      Throws:
        `java.lang.IllegalArgumentException` - if the params argument is inappropriate.