Class Signature
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-256. The DSA algorithm using the
SHA-256 message digest algorithm can be specified as SHA256withDSA
.
In the case of RSA the signing algorithm could be specified as, for example,
SHA256withRSA
.
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:
- 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)
andinitSign(PrivateKey, SecureRandom)
).
- a public key, which initializes the signature for
verification (see
- 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 theverify
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:
SHA1withDSA
SHA256withDSA
SHA1withRSA
SHA256withRSA
- Since:
- 1.1
-
Field Summary
Modifier and TypeFieldDescriptionprotected static final int
Possiblestate
value, signifying that thisSignature
object has been initialized for signing.protected int
Current state of thisSignature
object.protected static final int
Possiblestate
value, signifying that thisSignature
object has not yet been initialized.protected static final int
Possiblestate
value, signifying that thisSignature
object has been initialized for verification.Fields declared in class java.security.SignatureSpi
appRandom
-
Constructor Summary
-
Method Summary
Modifier and TypeMethodDescriptionclone()
Returns a clone if the implementation is cloneable.final String
Returns the name of the algorithm for thisSignature
object.static Signature
getInstance
(String algorithm) Returns aSignature
object that implements the specified signature algorithm.static Signature
getInstance
(String algorithm, String provider) Returns aSignature
object that implements the specified signature algorithm.static Signature
getInstance
(String algorithm, Provider provider) Returns aSignature
object that implements the specified signature algorithm.final Object
getParameter
(String param) Deprecated.final AlgorithmParameters
Returns the parameters used with thisSignature
object.final Provider
Returns the provider of thisSignature
object.final void
initSign
(PrivateKey privateKey) Initialize this object for signing.final void
initSign
(PrivateKey privateKey, SecureRandom random) Initialize this object for signing.final void
initVerify
(Certificate certificate) Initializes this object for verification, using the public key from the given certificate.final void
initVerify
(PublicKey publicKey) Initializes this object for verification.final void
setParameter
(String param, Object value) Deprecated.final void
setParameter
(AlgorithmParameterSpec params) Initializes thisSignature
object with the specified parameter values.final byte[]
sign()
Returns the signature bytes of all the data updated.final int
sign
(byte[] outbuf, int offset, int len) Finishes the signature operation and stores the resulting signature bytes in the provided bufferoutbuf
, starting atoffset
.toString()
Returns a string representation of thisSignature
object, providing information that includes the state of the object and the name of the algorithm used.final void
update
(byte b) Updates the data to be signed or verified by a byte.final void
update
(byte[] data) Updates the data to be signed or verified, using the specified array of bytes.final 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.final void
update
(ByteBuffer data) Updates the data to be signed or verified using the specified ByteBuffer.final boolean
verify
(byte[] signature) Verifies the passed-in signature.final boolean
verify
(byte[] signature, int offset, int length) Verifies the passed-in signature in the specified array of bytes, starting at the specified offset.Methods declared in class java.security.SignatureSpi
engineGetParameter, engineGetParameters, engineInitSign, engineInitSign, engineInitVerify, engineSetParameter, engineSetParameter, engineSign, engineSign, engineUpdate, engineUpdate, engineUpdate, engineVerify, engineVerify
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Field Details
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UNINITIALIZED
protected static final int UNINITIALIZEDPossiblestate
value, signifying that thisSignature
object has not yet been initialized.- See Also:
-
SIGN
protected static final int SIGNPossiblestate
value, signifying that thisSignature
object has been initialized for signing.- See Also:
-
VERIFY
protected static final int VERIFYPossiblestate
value, signifying that thisSignature
object has been initialized for verification.- See Also:
-
state
protected int stateCurrent state of thisSignature
object.
-
-
Constructor Details
-
Signature
Creates aSignature
object for the specified algorithm.- Parameters:
algorithm
- the standard string name of the algorithm. See the Signature section in the Java Security Standard Algorithm Names Specification for information about standard algorithm names.
-
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Method Details
-
getInstance
Returns aSignature
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 theSignatureSpi
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.- Implementation Note:
- The JDK Reference Implementation additionally uses the
jdk.security.provider.preferred
Security
property to determine the preferred provider order for the specified algorithm. This may be different from the order of providers returned bySecurity.getProviders()
. - Parameters:
algorithm
- the standard name of the algorithm requested. See the Signature section in the Java Security Standard Algorithm Names Specification for information about standard algorithm names.- Returns:
- the new
Signature
object - Throws:
NoSuchAlgorithmException
- if noProvider
supports aSignature
implementation for the specified algorithmNullPointerException
- ifalgorithm
isnull
- See Also:
-
getInstance
public static Signature getInstance(String algorithm, String provider) throws NoSuchAlgorithmException, NoSuchProviderException Returns aSignature
object that implements the specified signature algorithm.A new
Signature
object encapsulating theSignatureSpi
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.- Parameters:
algorithm
- the name of the algorithm requested. See the Signature section in the Java Security Standard Algorithm Names Specification for information about standard algorithm names.provider
- the name of the provider.- Returns:
- the new
Signature
object - Throws:
IllegalArgumentException
- if the provider name isnull
or emptyNoSuchAlgorithmException
- if aSignatureSpi
implementation for the specified algorithm is not available from the specified providerNoSuchProviderException
- if the specified provider is not registered in the security provider listNullPointerException
- ifalgorithm
isnull
- See Also:
-
getInstance
public static Signature getInstance(String algorithm, Provider provider) throws NoSuchAlgorithmException Returns aSignature
object that implements the specified signature algorithm.A new
Signature
object encapsulating theSignatureSpi
implementation from the specified provider is returned. Note that the specified provider does not have to be registered in the provider list.- Parameters:
algorithm
- the name of the algorithm requested. See the Signature section in the Java Security Standard Algorithm Names Specification for information about standard algorithm names.provider
- the provider.- Returns:
- the new
Signature
object - Throws:
IllegalArgumentException
- if the provider isnull
NoSuchAlgorithmException
- if aSignatureSpi
implementation for the specified algorithm is not available from the specifiedProvider
objectNullPointerException
- ifalgorithm
isnull
- Since:
- 1.4
- See Also:
-
getProvider
Returns the provider of thisSignature
object.- Returns:
- the provider of this
Signature
object
-
initVerify
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
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.- Since:
- 1.3
-
initSign
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
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 generatedrandom
- the source of randomness for thisSignature
object- Throws:
InvalidKeyException
- if the key is invalid.
-
sign
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 toinitSign(PrivateKey)
. That is, the object is reset and available to generate another signature from the same signer, if desired, via new calls toupdate
andsign
.- Returns:
- the signature bytes of the signing operation's result.
- Throws:
SignatureException
- if thisSignature
object is not initialized properly or if this signature algorithm is unable to process the input data provided.
-
sign
Finishes the signature operation and stores the resulting signature bytes in the provided bufferoutbuf
, starting atoffset
. 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 theinitSign
methods) and can be reused to generate further signatures with the same private key.- Parameters:
outbuf
- buffer for the signature result.offset
- offset intooutbuf
where the signature is stored.len
- number of bytes withinoutbuf
allotted for the signature.- Returns:
- the number of bytes placed into
outbuf
. - Throws:
SignatureException
- if thisSignature
object is not initialized properly, if this signature algorithm is unable to process the input data provided, or iflen
is less than the actual signature length.IllegalArgumentException
- ifoutbuf
isnull
, oroffset
orlen
is less than 0, or the sum ofoffset
andlen
is greater than the length ofoutbuf
.- Since:
- 1.2
-
verify
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 toinitVerify(PublicKey)
. That is, the object is reset and available to verify another signature from the identity whose public key was specified in the call toinitVerify
.- Parameters:
signature
- the signature bytes to be verified.- Returns:
true
if the signature was verified,false
if not.- Throws:
SignatureException
- if thisSignature
object is not initialized properly, the passed-in signature is improperly encoded or of the wrong type, if this signature algorithm is unable to process the input data provided, etc.
-
verify
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 toinitVerify(PublicKey)
. That is, the object is reset and available to verify another signature from the identity whose public key was specified in the call toinitVerify
.- 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 thisSignature
object is not initialized properly, the passed-in signature is improperly encoded or of the wrong type, if this signature algorithm is unable to process the input data provided, etc.IllegalArgumentException
- if thesignature
byte array isnull
, or theoffset
orlength
is less than 0, or the sum of theoffset
andlength
is greater than the length of thesignature
byte array.- Since:
- 1.4
-
update
Updates the data to be signed or verified by a byte.- Parameters:
b
- the byte to use for the update.- Throws:
SignatureException
- if thisSignature
object is not initialized properly.
-
update
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 thisSignature
object is not initialized properly.
-
update
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 thisSignature
object is not initialized properly.IllegalArgumentException
- ifdata
isnull
, oroff
orlen
is less than 0, or the sum ofoff
andlen
is greater than the length ofdata
.
-
update
Updates the data to be signed or verified using the specified ByteBuffer. Processes thedata.remaining()
bytes starting atdata.position()
. Upon return, the buffer's position will be equal to its limit; its limit will not have changed.- Parameters:
data
- the ByteBuffer- Throws:
SignatureException
- if thisSignature
object is not initialized properly.- Since:
- 1.5
-
getAlgorithm
Returns the name of the algorithm for thisSignature
object.- Returns:
- the name of the algorithm for this
Signature
object.
-
toString
-
setParameter
@Deprecated public final void setParameter(String param, Object value) throws InvalidParameterException Deprecated.UsesetParameter
.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 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 parametervalue
- the parameter value- Throws:
InvalidParameterException
- ifparam
is an invalid parameter for thisSignature
object, the parameter is already set and cannot be set again, a security exception occurs, and so on.- See Also:
-
setParameter
public final void setParameter(AlgorithmParameterSpec params) throws InvalidAlgorithmParameterException Initializes thisSignature
object with the specified parameter values.- Parameters:
params
- the parameter values- Throws:
InvalidAlgorithmParameterException
- if the given parameter values are inappropriate for thisSignature
object- See Also:
-
getParameters
Returns the parameters used with thisSignature
object.The returned parameters may be the same that were used to initialize this
Signature
object, or may contain additional default or random parameter values used by the underlying signature scheme. If the required parameters were not supplied and can be generated by theSignature
object, the generated parameters are returned; otherwisenull
is returned.However, if the signature scheme does not support returning the parameters as
AlgorithmParameters
,null
is always returned.- Returns:
- the parameters used with this
Signature
object, ornull
- Throws:
UnsupportedOperationException
- if the provider does not support this method- Since:
- 1.4
- See Also:
-
getParameter
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 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
- ifparam
is an invalid parameter for this engine, or another exception occurs while trying to get this parameter.- See Also:
-
clone
Returns a clone if the implementation is cloneable.- Overrides:
clone
in classSignatureSpi
- Returns:
- a clone if the implementation is cloneable.
- Throws:
CloneNotSupportedException
- if this is called on an implementation that does not supportCloneable
.- See Also:
-
setParameter
.