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 DSS,
* 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:
initVerify()), orsign() methods and the verify() method.Note that this class is abstract and extends from {@link SignatureSpi} for
* historical reasons. Application developers should only take notice of the
* methods defined in this Initializes this object for verification, using the public key from the
* given certificate. If the certificate is of type X.509 and has a key usage
* extension field marked as critical, and the value of the key
* usage extension field implies that the public key in the certificate
* and its corresponding private key are not supposed to be used for digital
* signatures, an {@link InvalidKeyException} is thrown. 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
* Finishes the signature operation and stores the resulting signature
* bytes in the provided buffer This signature object is reset to its initial state (the state it was
* in after a call to one of the 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
* Verifies the passed-in A call to this method resets this signature object to the state it was
* in when previously initialized for verification via a call to
* Returns the parameters used with this signature object. The returned parameters may be the same that were used to initialize
* this signature, or may contain a combination of default and randomly
* generated parameter values used by the underlying signature implementation
* if this signature requires algorithm parameters but was not initialized
* with any.
*
* @return the parameters used with this signature, or 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.
*
* @author Mark Benvenuto state value, signifying that this signature object
* has not yet been initialized.
*/
protected static final int UNINITIALIZED = 0;
// Constructor.
// ------------------------------------------------------------------------
/**
* Possible state value, signifying that this signature object
* has been initialized for signing.
*/
protected static final int SIGN = 2;
/**
* Possible state value, signifying that this signature object
* has been initialized for verification.
*/
protected static final int VERIFY = 3;
/** Current state of this signature object. */
protected int state = UNINITIALIZED;
private String algorithm;
Provider provider;
/**
* Creates a Signature object for the specified algorithm.
*
* @param 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.
*/
protected Signature(String algorithm)
{
this.algorithm = algorithm;
state = UNINITIALIZED;
}
/**
* 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.
*
* @param 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.
* @return the new Signature object.
* @throws NoSuchAlgorithmException if the algorithm is not available in the
* environment.
*/
public static Signature getInstance(String algorithm)
throws NoSuchAlgorithmException
{
Provider[] p = Security.getProviders();
for (int i = 0; i < p.length; i++)
{
try
{
return getInstance(algorithm, p[i]);
}
catch (NoSuchAlgorithmException ignored) {}
}
throw new NoSuchAlgorithmException(algorithm);
}
/**
* Generates a Signature object implementing the specified
* algorithm, as supplied from the specified provider, if such an algorithm
* is available from the provider.
*
* @param algorithm the name of the algorithm requested. See Appendix A in
* the Java Cryptography Architecture API Specification & Reference for
* information about standard algorithm names.
* @param provider the name of the provider.
* @return the new Signature object.
* @throws NoSuchAlgorithmException if the algorithm is not available in the
* package supplied by the requested provider.
* @throws NoSuchProviderException if the provider is not available in the
* environment.
* @throws IllegalArgumentException if the provider name is null
* or empty.
* @see Provider
*/
public static Signature getInstance(String algorithm, String provider)
throws NoSuchAlgorithmException, NoSuchProviderException
{
if (provider == null || provider.length() == 0)
throw new IllegalArgumentException("Illegal provider");
Provider p = Security.getProvider(provider);
if (p == null)
throw new NoSuchProviderException(provider);
return getInstance(algorithm, p);
}
/**
* Generates a Signature object implementing the specified
* algorithm, as supplied from the specified provider, if such an algorithm
* is available from the provider. Note: the provider doesn't have to be
* registered.
*
* @param algorithm the name of the algorithm requested. See Appendix A in
* the Java Cryptography Architecture API Specification & Reference for
* information about standard algorithm names.
* @param provider the provider.
* @return the new Signature object.
* @throws NoSuchAlgorithmException if the algorithm is not
* available in the package supplied by the requested provider.
* @throws IllegalArgumentException if the provider is
* null.
* @since 1.4
* @see Provider
*/
public static Signature getInstance(String algorithm, Provider provider)
throws NoSuchAlgorithmException
{
if (provider == null)
throw new IllegalArgumentException("Illegal provider");
Signature result = null;
Object o = Engine.getInstance(SIGNATURE, algorithm, provider);
if (o instanceof SignatureSpi)
{
result = new DummySignature((SignatureSpi) o, algorithm);
}
else if (o instanceof Signature)
{
result = (Signature) o;
result.algorithm = algorithm;
}
else
{
throw new NoSuchAlgorithmException(algorithm);
}
result.provider = provider;
return result;
}
/**
* Returns the provider of this signature object.
*
* @return the provider of this signature object.
*/
public final Provider getProvider()
{
return provider;
}
/**
* Initializes this object for verification. If this method is called again
* with a different argument, it negates the effect of this call.
*
* @param publicKey the public key of the identity whose signature is going
* to be verified.
* @throws InvalidKeyException if the key is invalid.
*/
public final void initVerify(PublicKey publicKey) throws InvalidKeyException
{
state = VERIFY;
engineInitVerify(publicKey);
}
/**
* 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().outbuf, starting at offset
* . The format of the signature depends on the underlying signature
* scheme.initSign() methods) and can be
* reused to generate further signatures with the same private key.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().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.
*/
public final boolean verify(byte[]signature) throws SignatureException
{
if (state == VERIFY)
{
state = UNINITIALIZED;
return engineVerify(signature);
}
else
throw new SignatureException();
}
/**
* signature in the specified array of
* bytes, starting at the specified offset.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().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.
* @throws IllegalArgumentException if the signature byte array
* is null, or the offset or length is
* less than 0, or the sum of the offset and
* length is greater than the length of the signature
* byte array.
*/
public final boolean verify(byte[] signature, int offset, int length)
throws SignatureException
{
if (state != VERIFY)
throw new SignatureException("illegal state");
if (signature == null)
throw new IllegalArgumentException("signaure is null");
if (offset < 0)
throw new IllegalArgumentException("offset is less than 0");
if (length < 0)
throw new IllegalArgumentException("length is less than 0");
if (offset + length < signature.length)
throw new IllegalArgumentException("range is out of bounds");
state = UNINITIALIZED;
return engineVerify(signature, offset, length);
}
/**
* Updates the data to be signed or verified by a byte.
*
* @param b the byte to use for the update.
* @throws SignatureException if this signature object is not initialized
* properly.
*/
public final void update(byte b) throws SignatureException
{
if (state != UNINITIALIZED)
engineUpdate(b);
else
throw new SignatureException();
}
/**
* Updates the data to be signed or verified, using the specified array of
* bytes.
*
* @param data the byte array to use for the update.
* @throws SignatureException if this signature object is not initialized
* properly.
*/
public final void update(byte[]data) throws SignatureException
{
if (state != UNINITIALIZED)
engineUpdate(data, 0, data.length);
else
throw new SignatureException();
}
/**
* Updates the data to be signed or verified, using the specified array of
* bytes, starting at the specified offset.
*
* @param data the array of bytes.
* @param off the offset to start from in the array of bytes.
* @param len the number of bytes to use, starting at offset.
* @throws SignatureException if this signature object is not initialized
* properly.
*/
public final void update(byte[]data, int off, int len)
throws SignatureException
{
if (state != UNINITIALIZED)
engineUpdate(data, off, len);
else
throw new SignatureException();
}
/**
* Returns the name of the algorithm for this signature object.
*
* @return the name of the algorithm for this signature object.
*/
public final String getAlgorithm()
{
return algorithm;
}
/**
* Returns a string representation of this signature object, providing
* information that includes the state of the object and the name of the
* algorithm used.
*
* @return a string representation of this signature object.
*/
public String toString()
{
return (algorithm + " Signature");
}
/**
* 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.
*
* @param param the string identifier of the parameter.
* @param 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.
* @see #getParameter(String)
* @deprecated Use setParameter(AlgorithmParameterSpec).
*/
public final void setParameter(String param, Object value)
throws InvalidParameterException
{
engineSetParameter(param, value);
}
/**
* Initializes this signature engine with the specified parameter set.
*
* @param params the parameters.
* @throws InvalidAlgorithmParameterException if the given parameters are
* inappropriate for this signature engine.
* @see #getParameters()
*/
public final void setParameter(AlgorithmParameterSpec params)
throws InvalidAlgorithmParameterException
{
engineSetParameter(params);
}
/**
* null if
* this signature does not use any parameters.
* @see #setParameter(AlgorithmParameterSpec)
*/
public final AlgorithmParameters getParameters()
{
return engineGetParameters();
}
/**
* 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.
*
* @param param the string name of the parameter.
* @return 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.
* @see #setParameter(String, Object)
* @deprecated
*/
public final Object getParameter(String param)
throws InvalidParameterException
{
return engineGetParameter(param);
}
/**
* Returns a clone if the implementation is cloneable.
*
* @return a clone if the implementation is cloneable.
* @throws CloneNotSupportedException if this is called on an implementation
* that does not support {@link Cloneable}.
*/
public Object clone() throws CloneNotSupportedException
{
throw new CloneNotSupportedException();
}
}