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java.security
Class Signature

java.lang.Object
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  +--java.security.SignatureSpi
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        +--java.security.Signature

public abstract class Signature

extends SignatureSpi

This Signature class is used to provide applications the functionality of a digital signature algorithm. Digital signatures are used for authentication and integrity assurance of digital data.

The signature algorithm can be, among others, the NIST standard DSA, using DSA and SHA-1. The DSA algorithm using the SHA-1 message digest algorithm can be specified as SHA1withDSA. In the case of RSA, there are multiple choices for the message digest algorithm, so the signing algorithm could be specified as, for example, MD2withRSA, MD5withRSA, or SHA1withRSA. The algorithm name must be specified, as there is no default.

Like other algorithm-based classes in Java Security, Signature provides implementation-independent algorithms, whereby a caller (application code) requests a particular signature algorithm and is handed back a properly initialized Signature object. It is also possible, if desired, to request a particular algorithm from a particular provider. See the getInstance methods.

Thus, there are two ways to request a Signature algorithm object: by specifying either just an algorithm name, or both an algorithm name and a package provider.

• If just an algorithm name is specified, the system will determine if there is an implementation of the algorithm requested available in the environment, and if there is more than one, if there is a preferred one.

• If both an algorithm name and a package provider are specified, the system will determine if there is an implementation of the algorithm in the package requested, and throw an exception if there is not.

A Signature object can be used to generate and verify digital signatures.

There are three phases to the use of a Signature object for either signing data or verifying a signature:

1. Initialization, with either
   • a public key, which initializes the signature for verification (see initVerify), or
   • a private key (and optionally a Secure Random Number Generator), which initializes the signature for signing (see initSign(PrivateKey) and initSign(PrivateKey, SecureRandom)).

2. Updating

   Depending on the type of initialization, this will update the bytes to be signed or verified. See the update methods.

3. Signing or Verifying a signature on all updated bytes. See the sign methods and the verify method.

Note that this class is abstract and extends from SignatureSpi for historical reasons. Application developers should only take notice of the methods defined in this Signature class; all the methods in the superclass are intended for cryptographic service providers who wish to supply their own implementations of digital signature algorithms.

Field Summary

protected static int	SIGN Possible state value, signifying that this signature object has been initialized for signing.
protected int	state Current state of this signature object.
protected static int	UNINITIALIZED Possible state value, signifying that this signature object has not yet been initialized.
protected static int	VERIFY Possible state value, signifying that this signature object has been initialized for verification.

Fields inherited from class java.security.SignatureSpi

appRandom

Constructor Summary

protected

Signature(String algorithm) Creates a Signature object for the specified algorithm.

Method Summary

Object	clone() Returns a clone if the implementation is cloneable.
String	getAlgorithm() Returns the name of the algorithm for this signature object.
static Signature	getInstance(String algorithm) Generates a Signature object that implements the specified digest algorithm.
static Signature	getInstance(String algorithm, String provider) Generates a Signature object implementing the specified algorithm, as supplied from the specified provider, if such an algorithm is available from the provider.
Object	getParameter(String param) Deprecated.
Provider	getProvider() Returns the provider of this signature object.
void	initSign(PrivateKey privateKey) Initialize this object for signing.
void	initSign(PrivateKey privateKey, SecureRandom random) Initialize this object for signing.
void	initVerify(PublicKey publicKey) Initializes this object for verification.
void	setParameter(AlgorithmParameterSpec params) Initializes this signature engine with the specified parameter set.
void	setParameter(String param, Object value) Deprecated. Use setParameter.
byte[]	sign() Returns the signature bytes of all the data updated.
int	sign(byte[] outbuf, int offset, int len) Finishes the signature operation and stores the resulting signature bytes in the provided buffer outbuf, starting at offset.
String	toString() Returns a string representation of this signature object, providing information that includes the state of the object and the name of the algorithm used.
void	update(byte b) Updates the data to be signed or verified by a byte.
void	update(byte[] data) Updates the data to be signed or verified, using the specified array of bytes.
void	update(byte[] data, int off, int len) Updates the data to be signed or verified, using the specified array of bytes, starting at the specified offset.
boolean	verify(byte[] signature) Verifies the passed-in signature.

Methods inherited from class java.security.SignatureSpi

engineGetParameter, engineInitSign, engineInitSign, engineInitVerify, engineSetParameter, engineSetParameter, engineSign, engineSign, engineUpdate, engineUpdate, engineVerify

Methods inherited from class java.lang.Object

equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

UNINITIALIZED

protected static final int UNINITIALIZED

Possible state value, signifying that this signature object has not yet been initialized.

SIGN

protected static final int SIGN

Possible state value, signifying that this signature object has been initialized for signing.

VERIFY

protected static final int VERIFY

Possible state value, signifying that this signature object has been initialized for verification.

state

protected int state

Current state of this signature object.

Constructor Detail

Signature

protected Signature(String algorithm)

Creates a Signature object for the specified algorithm.

Parameters:

algorithm - the standard string name of the algorithm. See Appendix A in the Java Cryptography Architecture API Specification & Reference for information about standard algorithm names.

Method Detail

getInstance

public static Signature getInstance(String algorithm)
                             throws NoSuchAlgorithmException

Generates a Signature object that implements the specified digest algorithm. If the default provider package provides an implementation of the requested digest algorithm, an instance of Signature containing that implementation is returned. If the algorithm is not available in the default package, other packages are searched.

Parameters:

algorithm - the standard name of the algorithm requested. See Appendix A in the Java Cryptography Architecture API Specification & Reference for information about standard algorithm names.

Returns:

the new Signature object.

Throws:

NoSuchAlgorithmException - if the algorithm is not available in the environment.

getInstance

public static Signature getInstance(String algorithm,
                                    String provider)
                             throws NoSuchAlgorithmException,
                                    NoSuchProviderException

Generates a Signature object implementing the specified algorithm, as supplied from the specified provider, if such an algorithm is available from the provider.

Parameters:

algorithm - the name of the algorithm requested. See Appendix A in the Java Cryptography Architecture API Specification & Reference for information about standard algorithm names.

provider - the name of the provider.

Returns:

the new Signature object.

Throws:

NoSuchAlgorithmException - if the algorithm is not available in the package supplied by the requested provider.

NoSuchProviderException - if the provider is not available in the environment.

See Also:

Provider

getProvider

public final Provider getProvider()

Returns the provider of this signature object.

Returns:

the provider of this signature object

initVerify

public final void initVerify(PublicKey publicKey)
                      throws InvalidKeyException

Initializes this object for verification. If this method is called again with a different argument, it negates the effect of this call.

Parameters:

publicKey - the public key of the identity whose signature is going to be verified.

Throws:

InvalidKeyException - if the key is invalid.

initSign

public final void initSign(PrivateKey privateKey)
                    throws InvalidKeyException

Initialize this object for signing. If this method is called again with a different argument, it negates the effect of this call.

Parameters:

privateKey - the private key of the identity whose signature is going to be generated.

Throws:

InvalidKeyException - if the key is invalid.

initSign

public final void initSign(PrivateKey privateKey,
                           SecureRandom random)
                    throws InvalidKeyException

Initialize this object for signing. If this method is called again with a different argument, it negates the effect of this call.

Parameters:

privateKey - the private key of the identity whose signature is going to be generated.

random - the source of randomness for this signature.

Throws:

InvalidKeyException - if the key is invalid.

sign

public final byte[] sign()
                  throws SignatureException

Returns the signature bytes of all the data updated. The format of the signature depends on the underlying signature scheme.

A call to this method resets this signature object to the state it was in when previously initialized for signing via a call to initSign(PrivateKey). That is, the object is reset and available to generate another signature from the same signer, if desired, via new calls to update and sign.

Returns:

the signature bytes of the signing operation's result.

Throws:

SignatureException - if this signature object is not initialized properly.

sign

public final int sign(byte[] outbuf,
                      int offset,
                      int len)
               throws SignatureException

Finishes the signature operation and stores the resulting signature bytes in the provided buffer outbuf, starting at offset. The format of the signature depends on the underlying signature scheme.

This signature object is reset to its initial state (the state it was in after a call to one of the initSign methods) and can be reused to generate further signatures with the same private key.

Parameters:

outbuf - buffer for the signature result.

offset - offset into outbuf where the signature is stored.

len - number of bytes within outbuf allotted for the signature.

Returns:

the number of bytes placed into outbuf.

Throws:

SignatureException - if an error occurs or len is less than the actual signature length.

Since:

JDK1.2

verify

public final boolean verify(byte[] signature)
                     throws SignatureException

Verifies the passed-in signature.

A call to this method resets this signature object to the state it was in when previously initialized for verification via a call to initVerify(PublicKey). That is, the object is reset and available to verify another signature from the identity whose public key was specified in the call to initVerify.

Parameters:

signature - the signature bytes to be verified.

Returns:

true if the signature was verified, false if not.

Throws:

SignatureException - if this signature object is not initialized properly, or the passed-in signature is improperly encoded or of the wrong type, etc.

update

public final void update(byte b)
                  throws SignatureException

Updates the data to be signed or verified by a byte.

Parameters:

b - the byte to use for the update.

Throws:

SignatureException - if this signature object is not initialized properly.

update

public final void update(byte[] data)
                  throws SignatureException

Updates the data to be signed or verified, using the specified array of bytes.

Parameters:

data - the byte array to use for the update.

Throws:

SignatureException - if this signature object is not initialized properly.

update

public final void update(byte[] data,
                         int off,
                         int len)
                  throws SignatureException

Updates the data to be signed or verified, using the specified array of bytes, starting at the specified offset.

Parameters:

data - the array of bytes.

off - the offset to start from in the array of bytes.

len - the number of bytes to use, starting at offset.

Throws:

SignatureException - if this signature object is not initialized properly.

getAlgorithm

public final String getAlgorithm()

Returns the name of the algorithm for this signature object.

Returns:

the name of the algorithm for this signature object.

toString

public String toString()

Returns a string representation of this signature object, providing information that includes the state of the object and the name of the algorithm used.

Overrides:

toString in class Object

Returns:

a string representation of this signature object.

setParameter

public final void setParameter(String param,
                               Object value)
                        throws InvalidParameterException

Deprecated. Use setParameter.

Sets the specified algorithm parameter to the specified value. This method supplies a general-purpose mechanism through which it is possible to set the various parameters of this object. A parameter may be any settable parameter for the algorithm, such as a parameter size, or a source of random bits for signature generation (if appropriate), or an indication of whether or not to perform a specific but optional computation. A uniform algorithm-specific naming scheme for each parameter is desirable but left unspecified at this time.

Parameters:

param - the string identifier of the parameter.

value - the parameter value.

Throws:

InvalidParameterException - if param is an invalid parameter for this signature algorithm engine, the parameter is already set and cannot be set again, a security exception occurs, and so on.

setParameter

public final void setParameter(AlgorithmParameterSpec params)
                        throws InvalidAlgorithmParameterException

Initializes this signature engine with the specified parameter set.

Parameters:

params - the parameters

Throws:

InvalidAlgorithmParameterException - if the given parameters are inappropriate for this signature engine

getParameter

public final Object getParameter(String param)
                          throws InvalidParameterException

Deprecated.

Gets the value of the specified algorithm parameter. This method supplies a general-purpose mechanism through which it is possible to get the various parameters of this object. A parameter may be any settable parameter for the algorithm, such as a parameter size, or a source of random bits for signature generation (if appropriate), or an indication of whether or not to perform a specific but optional computation. A uniform algorithm-specific naming scheme for each parameter is desirable but left unspecified at this time.

Parameters:

param - the string name of the parameter.

Returns:

the object that represents the parameter value, or null if there is none.

Throws:

InvalidParameterException - if param is an invalid parameter for this engine, or another exception occurs while trying to get this parameter.

clone

public Object clone()
             throws CloneNotSupportedException

Returns a clone if the implementation is cloneable.

Overrides:

clone in class SignatureSpi

Returns:

a clone if the implementation is cloneable.

Throws:

CloneNotSupportedException - if this is called on an implementation that does not support Cloneable.