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## 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 one of the `getInstance` factory methods of the `Cipher` engine class 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/mode/padding" or

- "algorithm"

(in the latter case, provider-specific default values for the mode and padding scheme are used). For example, the following is a valid transformation:

         Cipher c = Cipher.getInstance("DES/CBC/PKCS5Padding");

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 or algorithm//padding (note the double slashes), in which case the requested mode and/or padding are set automatically by the `getInstance` methods of `Cipher`, which invoke the `engineSetMode` and `engineSetPadding` methods of the provider's subclass of `CipherSpi`.

A `Cipher` property in a provider master class may have one of the following formats:

-          // provider's subclass of "CipherSpi" implements "algName" with
           // pluggable mode and padding
           Cipher.algName

-          // provider's subclass of "CipherSpi" implements "algName" in the
           // specified "mode", with pluggable padding
           Cipher.algName/mode

-          // provider's subclass of "CipherSpi" implements "algName" with the
           // specified "padding", with pluggable mode
           Cipher.algName//padding

-          // provider's subclass of "CipherSpi" implements "algName" with the
           // specified "mode" and "padding"
           Cipher.algName/mode/padding

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. That provider would have the following `Cipher` properties in its master class:

-          Cipher.DES/ECB/PKCS5Padding

-          Cipher.DES/CBC/PKCS5Padding

-          Cipher.DES/CFB/PKCS5Padding

-          Cipher.DES/OFB/PKCS5Padding

Another 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`. That provider would have the following `Cipher` properties in its master class:

-          Cipher.DES

The `getInstance` factory method of the `Cipher` engine class follows these rules in order to instantiate a provider's implementation of `CipherSpi` for a transformation of the form "algorithm":

1. Check if the provider has registered a subclass of `CipherSpi` for the specified "algorithm".

   If the answer is YES, instantiate this class, for whose mode and padding scheme default values (as supplied by the provider) are used.

   If the answer is NO, throw a `NoSuchAlgorithmException` exception.

The `getInstance` factory method of the `Cipher` engine class follows these rules in order to instantiate a provider's implementation of `CipherSpi` for a transformation of the form "algorithm/mode/padding":

1. Check if the provider has registered a subclass of `CipherSpi` for the specified "algorithm/mode/padding" transformation.

   If the answer is YES, instantiate it.

   If the answer is NO, go to the next step.

2. Check if the provider has registered a subclass of `CipherSpi` for the sub-transformation "algorithm/mode".

   If the answer is YES, instantiate it, and call `engineSetPadding(padding)` on the new instance.

   If the answer is NO, go to the next step.

3. Check if the provider has registered a subclass of `CipherSpi` for the sub-transformation "algorithm//padding" (note the double slashes).

   If the answer is YES, instantiate it, and call `engineSetMode(mode)` on the new instance.

   If the answer is NO, go to the next step.

4. Check if the provider has registered a subclass of `CipherSpi` for the sub-transformation "algorithm".

   If the answer is YES, instantiate it, and call `engineSetMode(mode)` and `engineSetPadding(padding)` on the new instance.

   If the answer is NO, throw a `NoSuchAlgorithmException` exception.

Since:
  1.4
See Also:
  `KeyGenerator`, `SecretKey`

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 int` | `engineGetKeySize(Key key)` Returns the key size of the given key object in bits.
`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 Key` | `engineUnwrap(byte[] wrappedKey, String wrappedKeyAlgorithm, int wrappedKeyType)` Unwrap a previously wrapped key.
`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.
`protected byte[]` | `engineWrap(Key key)` Wrap a key.

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

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.

### 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 a combination of default and random parameter values used by the underlying cipher implementation if this cipher requires algorithm parameters but was not initialized with any.

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

### 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 one of the following four operations: encryption, decryption, key wrapping or key unwrapping, depending on the value of `opmode`.

  If this cipher requires any algorithm parameters that cannot be derived from the given `key`, 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 or key wrapping, and raise an `InvalidKeyException` if it is being initialized for decryption or key unwrapping. The generated parameters can be retrieved using `engineGetParameters` or `engineGetIV` (if the parameter is an IV).

  If this cipher (including its underlying feedback or padding scheme) requires any random bytes (e.g., for parameter generation), 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 one of the following: `ENCRYPT_MODE`, `DECRYPT_MODE`, `WRAP_MODE` or `UNWRAP_MODE`)
    `key` - the encryption key
    `random` - the source of randomness
  Throws:
    `InvalidKeyException` - if the given key is inappropriate for initializing this cipher, or if this cipher is being initialized for decryption and requires algorithm parameters that cannot be determined from the given key.

### 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 one of the following four operations: encryption, decryption, key wrapping or key unwrapping, depending on the value of `opmode`.

  If 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 or key wrapping, and raise an `InvalidAlgorithmParameterException` if it is being initialized for decryption or key unwrapping. The generated parameters can be retrieved using `engineGetParameters` or `engineGetIV` (if the parameter is an IV).

  If this cipher (including its underlying feedback or padding scheme) requires any random bytes (e.g., for parameter generation), 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 one of the following: `ENCRYPT_MODE`, `DECRYPT_MODE`, `WRAP_MODE` or `UNWRAP_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.

### 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 one of the following four operations: encryption, decryption, key wrapping or key unwrapping, depending on the value of `opmode`.

  If 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 or key wrapping, and raise an `InvalidAlgorithmParameterException` if it is being initialized for decryption or key unwrapping. The generated parameters can be retrieved using `engineGetParameters` or `engineGetIV` (if the parameter is an IV).

  If this cipher (including its underlying feedback or padding scheme) requires any random bytes (e.g., for parameter generation), 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 one of the following: `ENCRYPT_MODE`, `DECRYPT_MODE`, `WRAP_MODE` or `UNWRAP_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` inclusive, 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` inclusive, are processed, and the result is stored in the `output` buffer, starting at `outputOffset` inclusive.

  If the `output` buffer is too small to hold the result, a `ShortBufferException` is thrown.

  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` inclusive, 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.

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

  Note: if any exception is thrown, this cipher object may need to be reset before it can be used again.

  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` inclusive, 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` inclusive.

  If the `output` buffer is too small to hold the result, a `ShortBufferException` is thrown.

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

  Note: if any exception is thrown, this cipher object may need to be reset before it can be used again.

  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:
    `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

### engineWrap

    protected byte[] engineWrap(Key key)
                         throws IllegalBlockSizeException,
                                InvalidKeyException

  Wrap a key.

  This concrete method has been added to this previously-defined abstract class. (For backwards compatibility, it cannot be abstract.) It may be overridden by a provider to wrap a key. Such an override is expected to throw an IllegalBlockSizeException or InvalidKeyException (under the specified circumstances), if the given key cannot be wrapped. If this method is not overridden, it always throws an UnsupportedOperationException.

  Parameters:
    `key` - the key to be wrapped.
  Returns:
    the wrapped key.
  Throws:
    `IllegalBlockSizeException` - if this cipher is a block cipher, no padding has been requested, and the length of the encoding of the key to be wrapped is not a multiple of the block size.
    `InvalidKeyException` - if it is impossible or unsafe to wrap the key with this cipher (e.g., a hardware protected key is being passed to a software-only cipher).

### engineUnwrap

    protected Key engineUnwrap(byte[] wrappedKey,
                               String wrappedKeyAlgorithm,
                               int wrappedKeyType)
                        throws InvalidKeyException,
                               NoSuchAlgorithmException

  Unwrap a previously wrapped key.

  This concrete method has been added to this previously-defined abstract class. (For backwards compatibility, it cannot be abstract.) It may be overridden by a provider to unwrap a previously wrapped key. Such an override is expected to throw an InvalidKeyException if the given wrapped key cannot be unwrapped. If this method is not overridden, it always throws an UnsupportedOperationException.

  Parameters:
    `wrappedKey` - the key to be unwrapped.
    `wrappedKeyAlgorithm` - the algorithm associated with the wrapped key.
    `wrappedKeyType` - the type of the wrapped key. This is one of `SECRET_KEY`, `PRIVATE_KEY`, or `PUBLIC_KEY`.
  Returns:
    the unwrapped key.
  Throws:
    `InvalidKeyException` - if `wrappedKey` does not represent a wrapped key, or if the algorithm associated with the wrapped key is different from `wrappedKeyAlgorithm` and/or its key type is different from `wrappedKeyType`.
    `NoSuchAlgorithmException` - if no installed providers can create keys for the `wrappedKeyAlgorithm`.

### engineGetKeySize

    protected int engineGetKeySize(Key key)
                            throws InvalidKeyException

  Returns the key size of the given key object in bits.

  This concrete method has been added to this previously-defined abstract class. It throws an `UnsupportedOperationException` if it is not overridden by the provider.

  Parameters:
    `key` - the key object.
  Returns:
    the key size of the given key object.
  Throws:
    `InvalidKeyException` - if `key` is invalid.

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