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

org.bouncycastle.crypto.modes

## Class CTSBlockCipher

- java.lang.Object
- - org.bouncycastle.crypto.BufferedBlockCipher
  - - org.bouncycastle.crypto.DefaultBufferedBlockCipher
    - - org.bouncycastle.crypto.modes.CTSBlockCipher

-     public class CTSBlockCipher
      extends DefaultBufferedBlockCipher

  A Cipher Text Stealing (CTS) mode cipher. CTS allows block ciphers to be used to produce cipher text which is the same length as the plain text.

- - ### Field Summary

    - ### Fields inherited from class org.bouncycastle.crypto.DefaultBufferedBlockCipher

      `buf, bufOff, cipher, forEncryption, mbCipher, partialBlockOkay, pgpCFB`

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `CTSBlockCipher(BlockCipher cipher)` Create a buffered block cipher that uses Cipher Text Stealing

  - ### Method Summary

    All Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `int` | `doFinal(byte[] out, int outOff)` Process the last block in the buffer.
    `int` | `getOutputSize(int len)` return the size of the output buffer required for an update plus a doFinal with an input of len bytes.
    `int` | `getUpdateOutputSize(int len)` return the size of the output buffer required for an update an input of len bytes.
    `int` | `processByte(byte in, byte[] out, int outOff)` process a single byte, producing an output block if necessary.
    `int` | `processBytes(byte[] in, int inOff, int len, byte[] out, int outOff)` process an array of bytes, producing output if necessary.

    - ### Methods inherited from class org.bouncycastle.crypto.DefaultBufferedBlockCipher

      `getBlockSize, getUnderlyingCipher, init, reset`

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

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

- - ### Constructor Detail

    - #### CTSBlockCipher

          public CTSBlockCipher(BlockCipher cipher)

      Create a buffered block cipher that uses Cipher Text Stealing
      Parameters:
        `cipher` - the underlying block cipher this buffering object wraps.

  - ### Method Detail

    - #### getUpdateOutputSize

          public int getUpdateOutputSize(int len)

      return the size of the output buffer required for an update an input of len bytes.
      Overrides:
        `getUpdateOutputSize` in class `DefaultBufferedBlockCipher`
      Parameters:
        `len` - the length of the input.
      Returns:
        the space required to accommodate a call to update with len bytes of input.

    - #### getOutputSize

          public int getOutputSize(int len)

      return the size of the output buffer required for an update plus a doFinal with an input of len bytes.
      Overrides:
        `getOutputSize` in class `DefaultBufferedBlockCipher`
      Parameters:
        `len` - the length of the input.
      Returns:
        the space required to accommodate a call to update and doFinal with len bytes of input.

    - #### processByte

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

      process a single byte, producing an output block if necessary.
      Overrides:
        `processByte` in class `DefaultBufferedBlockCipher`
      Parameters:
        `in` - the input byte.
        `out` - the space for any output that might be produced.
        `outOff` - the offset from which the output will be copied.
      Returns:
        the number of output bytes copied to out.
      Throws:
        `DataLengthException` - if there isn't enough space in out.
        `java.lang.IllegalStateException` - if the cipher isn't initialised.

    - #### processBytes

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

      process an array of bytes, producing output if necessary.
      Overrides:
        `processBytes` in class `DefaultBufferedBlockCipher`
      Parameters:
        `in` - the input byte array.
        `inOff` - the offset at which the input data starts.
        `len` - the number of bytes to be copied out of the input array.
        `out` - the space for any output that might be produced.
        `outOff` - the offset from which the output will be copied.
      Returns:
        the number of output bytes copied to out.
      Throws:
        `DataLengthException` - if there isn't enough space in out.
        `java.lang.IllegalStateException` - if the cipher isn't initialised.

    - #### doFinal

          public int doFinal(byte[] out,
                             int outOff)
                      throws DataLengthException,
                             java.lang.IllegalStateException,
                             InvalidCipherTextException

      Process the last block in the buffer.
      Overrides:
        `doFinal` in class `DefaultBufferedBlockCipher`
      Parameters:
        `out` - the array the block currently being held is copied into.
        `outOff` - the offset at which the copying starts.
      Returns:
        the number of output bytes copied to out.
      Throws:
        `DataLengthException` - if there is insufficient space in out for the output.
        `java.lang.IllegalStateException` - if the underlying cipher is not initialised.
        `InvalidCipherTextException` - if cipher text decrypts wrongly (in case the exception will never get thrown).