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java.security
abstract public class: Signature [javadoc | source]
java.lang.Object
   java.security.SignatureSpi
      java.security.Signature

Direct Known Subclasses:
    DummySignature, Delegate

The 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.

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

  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.

Every implementation of the Java platform is required to support the following standard Signature algorithms:

These algorithms are described in the Signature section of the Java Cryptography Architecture Standard Algorithm Name Documentation. Consult the release documentation for your implementation to see if any other algorithms are supported.
Field Summary
 Provider provider     
protected static final  int UNINITIALIZED    Possible #state value, signifying that this signature object has not yet been initialized. 
protected static final  int SIGN    Possible #state value, signifying that this signature object has been initialized for signing. 
protected static final  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 java.security.SignatureSpi:
appRandom
Constructor:
 protected Signature(String algorithm) 
    Creates a Signature object for the specified algorithm.
Method from java.security.Signature Summary:
chooseFirstProvider,   clone,   getAlgorithm,   getInstance,   getInstance,   getInstance,   getParameter,   getParameters,   getProvider,   initSign,   initSign,   initVerify,   initVerify,   setParameter,   setParameter,   sign,   sign,   toString,   update,   update,   update,   update,   verify,   verify
Methods from java.security.SignatureSpi:
clone,   engineGetParameter,   engineGetParameters,   engineInitSign,   engineInitSign,   engineInitVerify,   engineSetParameter,   engineSetParameter,   engineSign,   engineSign,   engineUpdate,   engineUpdate,   engineUpdate,   engineVerify,   engineVerify
Methods from java.lang.Object:
clone,   equals,   finalize,   getClass,   hashCode,   notify,   notifyAll,   toString,   wait,   wait,   wait
Method from java.security.Signature Detail:
  void chooseFirstProvider() 
 public Object clone() throws CloneNotSupportedException 
    Returns a clone if the implementation is cloneable.
 public final String getAlgorithm() 
    Returns the name of the algorithm for this signature object.
 public static Signature getInstance(String algorithm) throws NoSuchAlgorithmException 
    Returns a Signature object that implements the specified signature algorithm.

    This method traverses the list of registered security Providers, starting with the most preferred Provider. A new Signature object encapsulating the SignatureSpi implementation from the first Provider that supports the specified algorithm is returned.

    Note that the list of registered providers may be retrieved via the Security.getProviders() method.

 public static Signature getInstance(String algorithm,
    String provider) throws NoSuchAlgorithmException, NoSuchProviderException 
    Returns a Signature object that implements the specified signature algorithm.

    A new Signature object encapsulating the SignatureSpi implementation from the specified provider is returned. The specified provider must be registered in the security provider list.

    Note that the list of registered providers may be retrieved via the Security.getProviders() method.

 public static Signature getInstance(String algorithm,
    Provider provider) throws NoSuchAlgorithmException 
    Returns a Signature object that implements the specified signature algorithm.

    A new Signature object encapsulating the SignatureSpi implementation from the specified Provider object is returned. Note that the specified Provider object does not have to be registered in the provider list.

 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.
 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.

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

 public final  void setParameter(AlgorithmParameterSpec params) throws InvalidAlgorithmParameterException 
    Initializes this signature engine with the specified parameter set.
 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.
 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.

 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.

 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.
 public final  void update(byte b) throws SignatureException 
    Updates the data to be signed or verified by a byte.
 public final  void update(byte[] data) throws SignatureException 
    Updates the data to be signed or verified, using the specified array of bytes.
 public final  void update(ByteBuffer data) throws SignatureException 
    Updates the data to be signed or verified using the specified ByteBuffer. Processes the data.remaining() bytes starting at at data.position(). Upon return, the buffer's position will be equal to its limit; its limit will not have changed.
 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.
 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.

 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.