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Class Signature

java.lang.Object
java.security.SignatureSpi
java.security.Signature
public abstract class Signature extends SignatureSpi
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-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:

  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:

  • SHA1withDSA
  • SHA256withDSA
  • SHA1withRSA
  • SHA256withRSA
These algorithms are described in the Signature section of the Java Security Standard Algorithm Names Specification. Consult the release documentation for your implementation to see if any other algorithms are supported.
Since:
1.1

Field Summary

Modifier and Type Field Description
protected static final int SIGN
Possible state value, signifying that this Signature object has been initialized for signing.
protected int state
Current state of this Signature object.
protected static final int UNINITIALIZED
Possible state value, signifying that this Signature object has not yet been initialized.
protected static final int VERIFY
Possible state value, signifying that this Signature object has been initialized for verification.

Fields declared in class java.security.SignatureSpi

appRandom

Constructor Summary

Signature(String algorithm)
Modifier Constructor Description
protected
Creates a Signature object for the specified algorithm.

Method Summary

Modifier and Type Method Description
Object clone()
Returns a clone if the implementation is cloneable.
final String getAlgorithm()
Returns the name of the algorithm for this Signature object.
static Signature getInstance(String algorithm)
Returns a Signature object that implements the specified signature algorithm.
static Signature getInstance(String algorithm, String provider)
Returns a Signature object that implements the specified signature algorithm.
static Signature getInstance(String algorithm, Provider provider)
Returns a Signature object that implements the specified signature algorithm.
final Object getParameter(String param)
Deprecated.
final AlgorithmParameters getParameters()
Returns the parameters used with this Signature object.
final Provider getProvider()
Returns the provider of this Signature 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.
Use setParameter.
final void setParameter(AlgorithmParameterSpec params)
Initializes this Signature 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 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.
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

Methods declared in class java.lang.Object

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

Field Details

UNINITIALIZED

protected static final int UNINITIALIZED
Possible state value, signifying that this Signature object has not yet been initialized.
See Also:

SIGN

protected static final int SIGN
Possible state value, signifying that this Signature object has been initialized for signing.
See Also:

VERIFY

protected static final int VERIFY
Possible state value, signifying that this Signature object has been initialized for verification.
See Also:

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 the Signature section in the Java Security Standard Algorithm Names Specification for information about standard algorithm names.

Method Details

getInstance

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.

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 by Security.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 no Provider supports a Signature implementation for the specified algorithm
NullPointerException - if algorithm is null
See Also:

getInstance

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.

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 is null or empty
NoSuchAlgorithmException - if a SignatureSpi implementation for the specified algorithm is not available from the specified provider
NoSuchProviderException - if the specified provider is not registered in the security provider list
NullPointerException - if algorithm is null
See Also:

getInstance

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 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 is null
NoSuchAlgorithmException - if a SignatureSpi implementation for the specified algorithm is not available from the specified Provider object
NullPointerException - if algorithm is null
Since:
1.4
See Also:

getProvider

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

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.
Since:
1.3

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 object
Throws:
InvalidKeyException - if the key is invalid.

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 or if this signature algorithm is unable to process the input data provided.

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 this Signature object is not initialized properly, if this signature algorithm is unable to process the input data provided, or if len is less than the actual signature length.
IllegalArgumentException - if outbuf is null, or offset or len is less than 0, or the sum of offset and len is greater than the length of outbuf.
Since:
1.2

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, 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

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, 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 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.
Since:
1.4

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.
IllegalArgumentException - if data is null, or off or len is less than 0, or the sum of off and len is greater than the length of data.

update

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 data.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 this Signature object is not initialized properly.
Since:
1.5

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.
Overrides:
toString in class Object
Returns:
a string representation of this Signature object.

setParameter

@Deprecated 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 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 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 this Signature object with the specified parameter values.
Parameters:
params - the parameter values
Throws:
InvalidAlgorithmParameterException - if the given parameter values are inappropriate for this Signature object
See Also:

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 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 the Signature object, the generated parameters are returned; otherwise null 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, or null
Throws:
UnsupportedOperationException - if the provider does not support this method
Since:
1.4
See Also:

getParameter

@Deprecated 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 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.
See Also:

clone

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

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Documentation extracted from Debian's OpenJDK Development Kit package.
Licensed under the GNU General Public License, version 2, with the Classpath Exception.
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https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/security/Signature.html