javax.crypto
Class CipherSpi

java.lang.Object
  |
  +--javax.crypto.CipherSpi

public abstract class CipherSpi
extends Object

This class defines the Service Provider Interface (SPI) for the Cipher class. All the abstract methods in this class must be implemented by each cryptographic service provider who wishes to supply the implementation of a particular cipher algorithm.

In order to create an instance of Cipher, which encapsulates an instance of this CipherSpi class, an application calls the getInstance method of Cipher and specifies the requested transformation. Optionally, the application may also specify the name of a provider.

A transformation is a string that describes the operation (or set of operations) to be performed on the given input, to produce some output. A transformation always includes the name of a cryptographic algorithm (e.g., DES), and may be followed by a feedback mode and padding scheme. A transformation is of the form: algorithm or algorithm/mode/padding (in the former case, defaults are used for mode and padding). For example, DES/CBC/PKCS5Padding represents a valid transformation.

A provider may supply a separate class for each combination of algorithm/mode/padding, or may decide to provide more generic classes representing sub-transformations corresponding to algorithm or algorithm/mode, whose mode and/or padding schemes can be set using engineSetMode and engineSetPadding, respectively.

For example, a provider may supply a subclass of CipherSpi that implements DES/ECB/PKCS5Padding, one that implements DES/CBC/PKCS5Padding, one that implements DES/CFB/PKCS5Padding, and yet another one that implements DES/OFB/PKCS5Padding.

A different provider may implement a class for each of the above modes (i.e., one class for ECB, one for CBC, one for CFB, and one for OFB), one class for PKCS5Padding, and a generic DES class that subclasses from CipherSpi.

The algorithm for instantiating a Cipher object (using one of the getInstance methods) when a transformation of the form algorithm is given is as follows:

The algorithm for instantiating a CipherSpi object when a transformation of the form algorithm/mode/padding is given is as follows:

See Also:
KeyGenerator, SecretKey, java.security.KeyPairGenerator, PublicKey, PrivateKey, AlgorithmParameters, AlgorithmParameterSpec

Field Summary
protected  int state
           
 
Constructor Summary
CipherSpi()
           
 
Method Summary
protected abstract  byte[] engineDoFinal(byte[] input, int inputOffset, int inputLen)
          Encrypts or decrypts data in a single-part operation, or finishes a multiple-part operation.
protected abstract  int engineDoFinal(byte[] input, int inputOffset, int inputLen, byte[] output, int outputOffset)
          Encrypts or decrypts data in a single-part operation, or finishes a multiple-part operation.
protected abstract  int engineGetBlockSize()
          Returns the block size (in bytes).
protected abstract  byte[] engineGetIV()
          Returns the initialization vector (IV) in a new buffer.
protected abstract  int engineGetOutputSize(int inputLen)
          Returns the length in bytes that an output buffer would need to be in order to hold the result of the next update or doFinal operation, given the input length inputLen (in bytes).
protected abstract  AlgorithmParameters engineGetParameters()
          Returns the parameters used with this cipher.
protected abstract  void engineInit(int opmode, Key key, AlgorithmParameterSpec params, SecureRandom random)
          Initializes this cipher with a key, a set of algorithm parameters and a source of randomness.
protected abstract  void engineInit(int opmode, Key key, AlgorithmParameters params, SecureRandom random)
          Initializes this cipher with a key, a set of algorithm parameters and a source of randomness.
protected abstract  void engineInit(int opmode, Key key, SecureRandom random)
          Initializes this cipher with a key and a source of randomness.
protected abstract  void engineSetMode(String mode)
          Sets the mode of this cipher.
protected abstract  void engineSetPadding(String padding)
          Sets the padding mechanism of this cipher.
protected abstract  byte[] engineUpdate(byte[] input, int inputOffset, int inputLen)
          Continues a multiple-part encryption or decryption operation (depending on how this cipher was initialized), processing another data part.
protected abstract  int engineUpdate(byte[] input, int inputOffset, int inputLen, byte[] output, int outputOffset)
          Continues a multiple-part encryption or decryption operation (depending on how this cipher was initialized), processing another data part.
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

state

protected int state
Constructor Detail

CipherSpi

public CipherSpi()
Method Detail

engineSetMode

protected abstract void engineSetMode(String mode)
                               throws NoSuchAlgorithmException
Sets the mode of this cipher.
Parameters:
mode - the cipher mode
Throws:
NoSuchAlgorithmException - if the requested cipher mode does not exist

engineSetPadding

protected abstract void engineSetPadding(String padding)
                                  throws NoSuchPaddingException
Sets the padding mechanism of this cipher.
Parameters:
padding - the padding mechanism
Throws:
NoSuchPaddingException - if the requested padding mechanism does not exist

engineGetBlockSize

protected abstract int engineGetBlockSize()

Returns the block size (in bytes).

Returns:
the block size (in bytes), or 0 if the underlying algorithm is not a block cipher

engineGetOutputSize

protected abstract int engineGetOutputSize(int inputLen)

Returns the length in bytes that an output buffer would need to be in order to hold the result of the next update or doFinal operation, given the input length inputLen (in bytes).

This call takes into account any unprocessed (buffered) data from a previous update call, and padding.

The actual output length of the next update or doFinal call may be smaller than the length returned by this method.

Parameters:
inputLen - - the input length (in bytes)
Returns:
the required output buffer size (in bytes)

engineGetIV

protected abstract byte[] engineGetIV()

Returns the initialization vector (IV) in a new buffer.

This is useful in the context of password-based encryption or decryption, where the IV is derived from a user-provided passphrase.

Returns:
the initialization vector in a new buffer, or null if the underlying algorithm does not use an IV, or if the IV has not yet been set.

engineInit

protected abstract void engineInit(int opmode,
                                   Key key,
                                   SecureRandom random)
                            throws InvalidKeyException

Initializes this cipher with a key and a source of randomness.

The cipher is initialized for encryption or decryption, depending on the value of opmode.

If this cipher requires an initialization vector (IV), it will get it from random. The random IV can be retrieved using getIV. This behaviour should only be used in encryption mode, however. When initializing a cipher that requires an IV for decryption, the IV (same IV that was used for encryption) must be provided explicitly as a parameter, in order to get the correct result. Note that when a Cipher object is initialized, it loses all previously-acquired state. In other words, initializing a Cipher is equivalent to creating a new instance of that Cipher, and initializing it.

Parameters:
opmode - the operation mode of this cipher (this is either ENCRYPT_MODE or DECRYPT_MODE)
key - the encryption key
random - the source of randomness
Throws:
InvalidKeyException - if the given key is inappropriate for initializing this cipher

engineInit

protected abstract void engineInit(int opmode,
                                   Key key,
                                   AlgorithmParameterSpec params,
                                   SecureRandom random)
                            throws InvalidKeyException,
                                   InvalidAlgorithmParameterException

Initializes this cipher with a key, a set of algorithm parameters and a source of randomness.

The cipher is initialized for encryption or decryption, depending on the value of opmode. If this cipher (including its underlying feedback or padding scheme) requires any random bytes, it will get them from random. Note that when a Cipher object is initialized, it loses all previously-acquired state. In other words, initializing a Cipher is equivalent to creating a new instance of that Cipher, and initializing it.

Parameters:
opmode - the operation mode of this cipher (this is either ENCRYPT_MODE or DECRYPT_MODE)
key - the encryption key
params - the algorithm parameters
random - the source of randomness
Throws:
InvalidKeyException - if the given key is inappropriate for initializing this cipher
InvalidAlgorithmParameterException - if the given algorithm parameters are inappropriate for this cipher

engineInit

protected abstract void engineInit(int opmode,
                                   Key key,
                                   AlgorithmParameters params,
                                   SecureRandom random)
                            throws InvalidKeyException,
                                   InvalidAlgorithmParameterException

Initializes this cipher with a key, a set of algorithm parameters and a source of randomness.

The cipher is initialized for encryption or decryption, depending on the value of opmode.

f this cipher requires any algorithm parameters and params is null, the underlying cipher implementation is supposed to generate the required parameters itself (using provider-specific default or random values) if it is being initialized for encryption, and raise an InvalidAlgorithmParameterException if it is being initialized for decryption. The generated parameters can be retrieved using engineGetParameters or engineGetIV (if the parameter is an IV).

Note that when a Cipher object is initialized, it loses all previously-acquired state. In other words, initializing a Cipher is equivalent to creating a new instance of that Cipher, and initializing it.

Parameters:
opmode - the operation mode of this cipher (this is either ENCRYPT_MODE or DECRYPT_MODE)
key - the encryption key
params - the algorithm parameters
random - the source of randomness
Throws:
InvalidKeyException - if the given key is inappropriate for initializing this cipher
InvalidAlgorithmParameterException - if the given algorithm parameters are inappropriate for this cipher, or if this cipher is being initialized for decryption and requires algorithm parameters and params is null

engineUpdate

protected abstract byte[] engineUpdate(byte[] input,
                                       int inputOffset,
                                       int inputLen)

Continues a multiple-part encryption or decryption operation (depending on how this cipher was initialized), processing another data part.

The first inputLen bytes in the input buffer, starting at inputOffset, are processed, and the result is stored in a new buffer.

Parameters:
input - the input buffer
inputOffset - the offset in input where the input starts
inputLen - the input length
Returns:
the new buffer with the result, or null if the underlying cipher is a block cipher and the input data is too short to result in a new block

engineUpdate

protected abstract int engineUpdate(byte[] input,
                                    int inputOffset,
                                    int inputLen,
                                    byte[] output,
                                    int outputOffset)
                             throws ShortBufferException

Continues a multiple-part encryption or decryption operation (depending on how this cipher was initialized), processing another data part.

The first inputLen bytes in the input buffer, starting at inputOffset, are processed, and the result is stored in the output buffer, starting at outputOffset.

If the output buffer is too small to hold the result, a ShortBufferException is thrown. In this case, repeat this call with a larger output buffer. Use getOutputSize to determine how big the output buffer should be.

Parameters:
input - the input buffer
inputOffset - the offset in input where the input starts
inputLen - the input length
output - the buffer for the result
outputOffset - the offset in output where the result is stored
Returns:
the number of bytes stored in output
Throws:
ShortBufferException - if the given output buffer is too small to hold the result

engineDoFinal

protected abstract byte[] engineDoFinal(byte[] input,
                                        int inputOffset,
                                        int inputLen)
                                 throws IllegalBlockSizeException,
                                        BadPaddingException

Encrypts or decrypts data in a single-part operation, or finishes a multiple-part operation. The data is encrypted or decrypted, depending on how this cipher was initialized.

The first inputLen bytes in the input buffer, starting at inputOffset, and any input bytes that may have been buffered during a previous update operation, are processed, with padding (if requested) being applied. The result is stored in a new buffer.

A call to this method resets this cipher object to the state it was in when previously initialized via a call to init. That is, the object is reset and available to encrypt or decrypt (depending on the operation mode that was specified in the call to init) more data.

Parameters:
input - the input buffer
inputOffset - the offset in input where the input starts
inputLen - the input length
Returns:
the new buffer with the result
Throws:
IllegalBlockSizeException - if this cipher is a block cipher, no padding has been requested (only in encryption mode), and the total input length of the data processed by this cipher is not a multiple of block size
BadPaddingException - if this cipher is in decryption mode, and (un)padding has been requested, but the decrypted data is not bounded by the appropriate padding bytes

engineDoFinal

protected abstract int engineDoFinal(byte[] input,
                                     int inputOffset,
                                     int inputLen,
                                     byte[] output,
                                     int outputOffset)
                              throws ShortBufferException,
                                     IllegalBlockSizeException,
                                     BadPaddingException

Encrypts or decrypts data in a single-part operation, or finishes a multiple-part operation. The data is encrypted or decrypted, depending on how this cipher was initialized.

The first inputLen bytes in the input buffer, starting at inputOffset, and any input bytes that may have been buffered during a previous update operation, are processed, with padding (if requested) being applied. The result is stored in the output buffer, starting at outputOffset.

If the output buffer is too small to hold the result, a ShortBufferException is thrown. In this case, repeat this call with a larger output buffer. Use getOutputSize to determine how big the output buffer should be.

A call to this method resets this cipher object to the state it was in when previously initialized via a call to init. That is, the object is reset and available to encrypt or decrypt (depending on the operation mode that was specified in the call to init) more data.

Parameters:
input - the input buffer
inputOffset - the offset in input where the input starts
inputLen - the input length
output - the buffer for the result
outputOffset - the offset in output where the result is
Returns:
the number of bytes stored in output
Throws:
IllegalBlockSizeException - if this cipher is a block cipher, no padding has been requested (only in encryption mode), and the total input length of the data processed by this cipher is not a multiple of block size
ShortBufferException - if the given output buffer is too small to hold the result
BadPaddingException - if this cipher is in decryption mode, and (un)padding has been requested, but the decrypted data is not bounded by the appropriate padding bytes

engineGetParameters

protected abstract AlgorithmParameters engineGetParameters()
Returns the parameters used with this cipher.

The returned parameters may be the same that were used to initialize this cipher, or may contain the default set of parameters or a set of randomly generated parameters used by the underlying cipher implementation (provided that the underlying cipher implementation uses a default set of parameters or creates new parameters if it needs parameters but was not initialized with any).

Returns:
the parameters used with this cipher, or null if this cipher does not use any parameters.