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Class javax.crypto.CipherSpi

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

public abstract class CipherSpi
extends Object
This class provides the functionality of a cryptographic cipher for encryption and decryption. It forms the core of the Java Cryptographic Extension (JCE) framework.

This class must be implemented by a provider who supports the above cryptographic services and wishes to register them with the Java Security Framework.

In order to create a Cipher object, the application calls the getInstance method of Cipher, and passes the name of the requested transformation to it. Optionally, the name of a provider may be specified.

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, provider-specific 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 Cipher 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 the PKCS5Padding scheme, and a generic DES class (subclass of Cipher), into which the above mode and padding classes can be "plugged into", using the engineSetMode and engineSetPadding methods.

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:

  1. Check if the provider has registered a subclass of Cipher 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 algorithm for instantiating a Cipher object when a transformation of the form algorithm/mode/padding is given is as follows:

  1. Check if the provider has registered a subclass of Cipher for the specified algorithm/mode/padding transformation. If the answer is YES, instantiate this class and return it to the user. If the answer is NO, go to the next step.
  2. Check if the provider has registered a subclass of Cipher for the sub-transformation algorithm/mode. If the answer is YES, instantiate this class, and call engineSetPadding(padding) on the new instance, before returning it to the user. If the answer is NO, go to the next step.
  3. Check if the provider has registered a subclass of Cipher for the sub-transformation algorithm. If the answer is YES, instantiate this class, and call engineSetMode(mode) and engineSetPadding(padding) on the new instance, before returning it to the user. If the answer is NO, throw a NoSuchAlgorithmException exception.

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

Constructor Index

 o CipherSpi()

Method Index

 o engineDoFinal(byte[], int, int)
Encrypts or decrypts data in a single-part operation, or finishes a multiple-part operation.
 o engineDoFinal(byte[], int, int, byte[], int)
Encrypts or decrypts data in a single-part operation, or finishes a multiple-part operation.
 o engineGetBlockSize()
Returns the block size (in bytes).
 o engineGetIV()
Returns the initialization vector (IV) in a new buffer.
 o engineGetOutputSize(int)
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).
 o engineInit(int, Key, AlgorithmParameterSpec, SecureRandom)
Initializes this cipher with a key, a set of algorithm parameters, and a source of randomness.
 o engineInit(int, Key, SecureRandom)
Initializes this cipher with a key and a source of randomness.
 o engineSetMode(String)
Sets the mode of this cipher.
 o engineSetPadding(String)
Sets the padding mechanism of this cipher.
 o engineUpdate(byte[], int, int)
Continues a multiple-part encryption or decryption operation (depending on how this cipher was initialized), processing another data part.
 o engineUpdate(byte[], int, int, byte[], int)
Continues a multiple-part encryption or decryption operation (depending on how this cipher was initialized), processing another data part.

Constructors

 o CipherSpi
public CipherSpi()

Methods

 o 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
 o 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
 o 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
 o 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)
 o 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.
 o 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
 o 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
Throws: InvalidAlgorithmParameterException
if the given algorithm parameters are inappropriate for this cipher
 o 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.
 o 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
 o 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.

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
Throws: 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
 o 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.

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
Throws: ShortBufferException
if the given output buffer is too small to hold the result
Throws: 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

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