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Class java.security.Signature
java.lang.Object
|
+----java.security.Signature
- public abstract class Signature
- extends Object
This Signature class is used to provide the functionality of a
digital signature algorithm, such as RSA with MD5 or
DSA. Digital signatures are used for authentication and
integrity assurance of digital data.
Like other algorithm-based classes in Java Security, the
Signature class has two major components:
- Digital Signature API (Application Program Interface)
- This is the interface of methods called by applications needing
digital signature services. The API consists of all public methods.
- Digital Signature SPI (Service Provider Interface)
- This is the interface implemented by providers that supply
specific algorithms. It consists of all methods whose names are
prefixed by
engine
. Each such method is called by a
correspondingly-named public API method. For example, the
engineSign
method is called by the
sign
method. The SPI methods are abstract;
providers must supply a concrete implementation.
Also 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, which initializes the signature for
signing (see initSign).
- 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 sign and verify.
-
SIGN
-
Possible state value, signifying that
this signature object has been initialized for signing.
-
state
-
Current state of this signature object.
-
UNINITIALIZED
-
Possible state value, signifying that
this signature object has not yet been initialized.
-
VERIFY
-
Possible state value, signifying that
this signature object has been initialized for verification.
-
Signature(String)
- Creates a Signature object for the specified algorithm.
-
clone()
- Returns a clone if the implementation is cloneable.
-
engineGetParameter(String)
- SPI: Gets the value of the specified algorithm parameter.
-
engineInitSign(PrivateKey)
- SPI: Initializes this signature object with the specified
private key for signing operations.
-
engineInitVerify(PublicKey)
- SPI: Initializes this signature object with the specified
public key for verification operations.
-
engineSetParameter(String, Object)
- SPI: Sets the specified algorithm parameter to the specified
value.
-
engineSign()
-
SPI: Returns the signature bytes of all the data
updated so far.
-
engineUpdate(byte)
- SPI: Updates the data to be signed or verified
using the specified byte.
-
engineUpdate(byte[], int, int)
- SPI: Updates the data to be signed or verified, using the
specified array of bytes, starting at the specified offset.
-
engineVerify(byte[])
-
SPI: Verifies the passed-in signature.
-
getAlgorithm()
-
Returns the name of the algorithm for this signature object.
-
getInstance(String)
- Generates a Signature object that implements the specified
algorithm.
-
getInstance(String, String)
-
Generates a Signature object implementing the specified
algorithm, as supplied from the specified provider, if such an
algorithm is available from the provider.
-
getParameter(String)
- Gets the value of the specified algorithm parameter.
-
initSign(PrivateKey)
- Initialize this object for signing.
-
initVerify(PublicKey)
- Initializes this object for verification.
-
setParameter(String, Object)
- Sets the specified algorithm parameter to the specified value.
-
sign()
- Returns the signature bytes of all the data updated.
-
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.
-
update(byte)
- Updates the data to be signed or verified by a byte.
-
update(byte[])
- Updates the data to be signed or verified, using the specified
array of bytes.
-
update(byte[], int, int)
- Updates the data to be signed or verified, using the specified
array of bytes, starting at the specified offset.
-
verify(byte[])
- Verifies the passed-in signature.
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.
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.
getInstance
public static Signature getInstance(String algorithm) throws NoSuchAlgorithmException
- Generates a Signature object that implements the specified
algorithm. If the default provider package contains a Signature
subclass implementing the algorithm, an instance of that subclass
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.
- Throws: NoSuchProviderException
- if the provider is not
available in the environment.
- See Also:
- Provider
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.
sign
public final byte[] sign() throws SignatureException
- Returns the signature bytes of all the data updated. The
signature returned is X.509-encoded.
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.
verify
public final boolean verify(byte signature[]) throws SignatureException
- Verifies the passed-in signature. The signature bytes are expected
to be X.509-encoded.
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.
- Returns:
- a string representation of this signature object.
- Overrides:
- toString in class Object
setParameter
public final void setParameter(String param,
Object value) throws InvalidParameterException
- 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.
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.
- 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.
engineInitVerify
protected abstract void engineInitVerify(PublicKey publicKey) throws InvalidKeyException
- SPI: Initializes this signature object with the specified
public key for verification operations.
- Parameters:
- publicKey - the public key of the identity whose signature is
going to be verified.
- Throws: InvalidKeyException
- if the key is improperly
encoded, parameters are missing, and so on.
engineInitSign
protected abstract void engineInitSign(PrivateKey privateKey) throws InvalidKeyException
- SPI: Initializes this signature object with the specified
private key for signing operations.
- Parameters:
- privateKey - the private key of the identity whose signature
will be generated.
- Throws: InvalidKeyException
- if the key is improperly
encoded, parameters are missing, and so on.
engineUpdate
protected abstract void engineUpdate(byte b) throws SignatureException
- SPI: Updates the data to be signed or verified
using the specified byte.
- Parameters:
- b - the byte to use for the update.
- Throws: SignatureException
- if the engine is not initialized
properly.
engineUpdate
protected abstract void engineUpdate(byte b[],
int off,
int len) throws SignatureException
- SPI: 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 the engine is not initialized
properly.
engineSign
protected abstract byte[] engineSign() throws SignatureException
- SPI: Returns the signature bytes of all the data
updated so far. The signature returned is X.509-encoded.
For more information about the X.509 encoding, see
X.509 certificates.
- Returns:
- the signature bytes of the signing operation's result.
- Throws: SignatureException
- if the engine is not
initialized properly.
engineVerify
protected abstract boolean engineVerify(byte sigBytes[]) throws SignatureException
- SPI: Verifies the passed-in signature. The signature bytes
are expected to be X.509-encoded. For more information about the
X.509 encoding, see X.509
certificates.
- Parameters:
- sigBytes - the signature bytes to be verified.
- Returns:
- true if the signature was verified, false if not.
- Throws: SignatureException
- if the engine is not initialized
properly, or the passed-in signature is improperly encoded or
of the wrong type, etc.
engineSetParameter
protected abstract void engineSetParameter(String param,
Object value) throws InvalidParameterException
- SPI: 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.
engineGetParameter
protected abstract Object engineGetParameter(String param) throws InvalidParameterException
- SPI: 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.
- Returns:
- a clone if the implementation is cloneable.
- Throws: CloneNotSupportedException
- if this is called
on an implementation that does not support
Cloneable
.
- Overrides:
- clone in class Object
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