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java.lang.Object | +----javax.crypto.CipherSpi
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:
(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":
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":
If the answer is YES, instantiate it.
If the answer is NO, go to the next step.
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.
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.
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.
public static final String ident
public CipherSpi()
protected abstract void engineSetMode(String mode) throws NoSuchAlgorithmException
protected abstract void engineSetPadding(String padding) throws NoSuchPaddingException
protected abstract int engineGetBlockSize()
protected abstract int engineGetOutputSize(int inputLen)
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.
protected abstract byte[] engineGetIV()
This is useful in the context of password-based encryption or decryption, where the IV is derived from a user-provided passphrase.
protected abstract AlgorithmParameters engineGetParameters()
The returned parameters may be the same that were used to initialise 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 initialised with any).
protected abstract void engineInit(int opmode, Key key, SecureRandom random) throws InvalidKeyException
The cipher is initialised for encryption or decryption, 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 initialised for encryption, and raise an InvalidKeyException if it is being initialised for decryption. 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 initialised, it loses all previously-acquired state. In other words, initialising a Cipher is equivalent to creating a new instance of that Cipher and initialising it
protected abstract void engineInit(int opmode, Key key, AlgorithmParameterSpec params, SecureRandom random) throws InvalidKeyException, InvalidAlgorithmParameterException
The cipher is initialised for encryption or decryption, 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 initialised for encryption, and raise an InvalidAlgorithmParameterException if it is being initialised for decryption. 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 initialised, it loses all previously-acquired state. In other words, initialising a Cipher is equivalent to creating a new instance of that Cipher and initialising it.
protected abstract void engineInit(int opmode, Key key, AlgorithmParameters params, SecureRandom random) throws InvalidKeyException, InvalidAlgorithmParameterException
The cipher is initialised for encryption or decryption, 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 initialised for encryption, and raise an InvalidAlgorithmParameterException if it is being initialised for decryption. 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 initialised, it loses all previously-acquired state. In other words, initialising a Cipher is equivalent to creating a new instance of that Cipher and initialising it.
protected abstract byte[] engineUpdate(byte input[], int inputOff, int inputLen)
The first inputLen bytes in the input buffer, starting at inputOffset, are processed, and the result is stored in a new buffer.
protected abstract int engineUpdate(byte input[], int inputOff, int inputLen, byte output[], int outputOff) throws ShortBufferException
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.
protected abstract byte[] engineDoFinal(byte input[], int inputOffset, int inputLen) throws IllegalBlockSizeException, BadPaddingException
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.
The cipher is reset to its initial state (uninitialised) after this call.
protected abstract int engineDoFinal(byte input[], int inputOff, int inputLen, byte output[], int outputOff) throws ShortBufferException, IllegalBlockSizeException, BadPaddingException
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.
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