java.security
Class Signature
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:
- 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.
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.
|
Signature(String algorithm) - Creates a
Signature object for the specified algorithm.
|
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)
|
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) - 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) .
|
clone , engineGetParameter , engineGetParameters , engineInitSign , engineInitSign , engineInitVerify , engineSetParameter , engineSetParameter , engineSign , engineSign , engineUpdate , engineUpdate , engineVerify , engineVerify |
clone , equals , finalize , getClass , hashCode , notify , notifyAll , toString , wait , wait , wait |
SIGN
protected static final int SIGN
Possible state
value, signifying that this signature object
has been initialized for signing.
UNINITIALIZED
protected static final int UNINITIALIZED
Possible state
value, signifying that this signature object
has not yet been initialized.
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.
Signature
protected Signature(String algorithm)
Creates a Signature
object for the specified algorithm.
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.
getAlgorithm
public final String getAlgorithm()
Returns the name of the algorithm for this signature object.
- 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.
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.
- the new Signature object.
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.
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.
- the new
Signature
object.
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.
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.
- the new
Signature
object.
getParameter
public final Object getParameter(String param)
throws InvalidParameterException
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
- the string name of the parameter.
- the object that represents the parameter value, or null if there
is none.
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.
- 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.
- 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.
privateKey
- the private key of the identity whose signature is going
to be generated.
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.
privateKey
- the private key of the identity whose signature is going
to be generated.random
- the source of randomness for this signature.
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.
publicKey
- the public key of the identity whose signature is going
to be verified.
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.
certificate
- the certificate of the identity whose signature is
going to be verified.
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
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.
param
- the string identifier of the parameter.value
- the parameter value.
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.
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()
.
- the signature bytes of the signing operation's result.
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.
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.
- the number of bytes placed into outbuf.
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.
- toString in interface Object
- 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.
b
- the byte to use for the update.
update
public final void update(byte[] data)
throws SignatureException
Updates the data to be signed or verified, using the specified array of
bytes.
data
- the byte array to use for the update.
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.
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.
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()
.
signature
- the signature bytes to be verified.
true
if the signature was verified, false
if not.
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()
.
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.
true
if the signature was verified, false
if not.
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.
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it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your option)
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02110-1301 USA.
Linking this library statically or dynamically with other modules is
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As a special exception, the copyright holders of this library give you
permission to link this library with independent modules to produce an
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