java.security

Class 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 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:

  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) ).
    • Updating
      Depending on the type of initialization, this will update the bytes to be signed or verified. See the update methods.
    • 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 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.
    protected int
    state
    Current state of this signature object.

    Fields inherited from class java.security.SignatureSpi

    appRandom

    Constructor Summary

    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.
    static Signature
    getInstance(String algorithm, Provider 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.
    AlgorithmParameters
    getParameters()
    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.

    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
    initVerify(Certificate certificate)
    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 InvalidKeyException is thrown.

    void
    setParameter(String param, Object value)
    Deprecated. Use setParameter(AlgorithmParameterSpec).
    void
    setParameter(AlgorithmParameterSpec params)
    Initializes this signature engine with the specified parameter set.
    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.

    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).

    boolean
    verify(byte[] signature, int offset, int length)
    Verifies the passed-in signature in the specified array of bytes, starting at the specified offset.

    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).

    Methods inherited from class java.security.SignatureSpi

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

    Methods inherited from class java.lang.Object

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

    Field Details

    SIGN

    protected static final int SIGN
    Possible state value, signifying that this signature object has been initialized for signing.
    Field Value:
    2

    UNINITIALIZED

    protected static final int UNINITIALIZED
    Possible state value, signifying that this signature object has not yet been initialized.
    Field Value:
    0

    VERIFY

    protected static final int VERIFY
    Possible state value, signifying that this signature object has been initialized for verification.
    Field Value:
    3

    state

    protected int state
    Current state of this signature object.

    Constructor Details

    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 Details

    clone

    public Object clone()
                throws CloneNotSupportedException
    Returns a clone if the implementation is cloneable.
    Overrides:
    clone in interface SignatureSpi
    Returns:
    a clone if the implementation is cloneable.
    Throws:
    CloneNotSupportedException - if this is called on an implementation that does not support Cloneable.

    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.

    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.
    IllegalArgumentException - if the provider name is null or empty.
    See Also:
    Provider

    getInstance

    public static Signature getInstance(String algorithm,
                                        Provider provider)
                throws NoSuchAlgorithmException
    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.
    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 provider.
    Returns:
    the new Signature object.
    Throws:
    NoSuchAlgorithmException - if the algorithm is not available in the package supplied by the requested provider.
    IllegalArgumentException - if the provider is null.
    Since:
    1.4
    See Also:
    Provider

    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.

    getParameters

    public final AlgorithmParameters getParameters()
    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.

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

    getProvider

    public final Provider getProvider()
    Returns the provider of this signature object.
    Returns:
    the provider of this signature object.

    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.

    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.

    initVerify

    public final void initVerify(Certificate certificate)
                throws InvalidKeyException
    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 InvalidKeyException is thrown.

    Parameters:
    certificate - the certificate of the identity whose signature is going to be verified.
    Throws:
    InvalidKeyException - if the public key in the certificate is not encoded properly or does not include required parameter information or cannot be used for digital signature purposes.

    setParameter

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

    Deprecated. Use setParameter(AlgorithmParameterSpec).

    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.

    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:
    1.2

    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 interface Object
    Returns:
    a string representation of this signature object.

    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.

    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.

    verify

    public final boolean verify(byte[] signature,
                                int offset,
                                int length)
                throws SignatureException
    Verifies the passed-in signature in the specified array of bytes, starting at the specified offset.

    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.
    offset - the offset to start from in the array of bytes.
    length - the number of bytes to use, starting at offset.
    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.
    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.

    Signature.java --- Signature Class Copyright (C) 1999, 2002, 2003, 2004 Free Software Foundation, Inc. This file is part of GNU Classpath. GNU Classpath is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2, or (at your option) any later version. GNU Classpath is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with GNU Classpath; see the file COPYING. If not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. Linking this library statically or dynamically with other modules is making a combined work based on this library. Thus, the terms and conditions of the GNU General Public License cover the whole combination. As a special exception, the copyright holders of this library give you permission to link this library with independent modules to produce an executable, regardless of the license terms of these independent modules, and to copy and distribute the resulting executable under terms of your choice, provided that you also meet, for each linked independent module, the terms and conditions of the license of that module. An independent module is a module which is not derived from or based on this library. If you modify this library, you may extend this exception to your version of the library, but you are not obligated to do so. If you do not wish to do so, delete this exception statement from your version.