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-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
   • 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)).
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.

Android provides the following Signature algorithms:

Algorithm	Supported API Levels
DSA	1+
DSAwithSHA1	1+
DSS	1-19
ECDSA	11+
ECDSAwithSHA1	11+
MD2withRSA	1-3
MD4withRSA	1-8
MD5withRSA	1+
MD5withRSA/ISO9796-2	1-8
NONEwithDSA	1+
NONEwithECDSA	11+
NONEwithRSA	17+
RSASSA-PSS	1-8
SHA1withDSA	1+
SHA1withECDSA	11+
SHA1withRSA	1+
SHA1withRSA/ISO9796-2	1-8
SHA1withRSA/PSS	23+
SHA224withDSA	20+
SHA224withECDSA	20+
SHA224withRSA	20+
SHA224withRSA/PSS	23+
SHA256withDSA	1+
SHA256withECDSA	11+
SHA256withRSA	1+
SHA256withRSA/PSS	23+
SHA384withECDSA	11+
SHA384withRSA	1+
SHA384withRSA/PSS	23+
SHA512withECDSA	11+
SHA512withRSA	1+
SHA512withRSA/PSS	23+

These algorithms are described in the Signature section of the Java Cryptography Architecture Standard Algorithm Name Documentation.

Constant Summary

int	SIGN	Possible state value, signifying that this signature object has been initialized for signing.
int	UNINITIALIZED	Possible state value, signifying that this signature object has not yet been initialized.
int	VERIFY	Possible state value, signifying that this signature object has been initialized for verification.

Field Summary

protected int

state

Current state of this signature object.

Inherited Field Summary

From class java.security.SignatureSpi

protected SecureRandom

appRandom

Application-specified source of randomness.

Protected Constructor Summary

Signature(String algorithm) Creates a Signature object for the specified algorithm.

Public Method Summary

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) This method is deprecated. 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, SecureRandom random) Initialize this object for signing.
final void	initSign(PrivateKey privateKey) Initialize this object for signing.
final void	initVerify(PublicKey publicKey) Initializes this object for verification.
final void	initVerify(Certificate certificate) Initializes this object for verification, using the public key from the given certificate.
final void	setParameter(AlgorithmParameterSpec params) Initializes this signature engine with the specified parameter set.
final void	setParameter(String param, Object value) This method is deprecated. Use setParameter.
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.
final byte[]	sign() Returns the signature bytes of all the data updated.
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[] 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 void	update(byte b) Updates the data to be signed or verified by a byte.
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.
final boolean	verify(byte[] signature) Verifies the passed-in signature.

Inherited Method Summary

From class java.security.SignatureSpi

Object	clone() Returns a clone if the implementation is cloneable.
abstract Object	engineGetParameter(String param) This method is deprecated. Deprecated.
AlgorithmParameters	engineGetParameters() This method is overridden by providers to return the parameters used with this signature engine, or null if this signature engine does not use any parameters.
void	engineInitSign(PrivateKey privateKey, SecureRandom random) Initializes this signature object with the specified private key and source of randomness for signing operations.
abstract void	engineInitSign(PrivateKey privateKey) Initializes this signature object with the specified private key for signing operations.
abstract void	engineInitVerify(PublicKey publicKey) Initializes this signature object with the specified public key for verification operations.
abstract void	engineSetParameter(String param, Object value) This method is deprecated. Replaced by engineSetParameter.
void	engineSetParameter(AlgorithmParameterSpec params) This method is overridden by providers to initialize this signature engine with the specified parameter set.
abstract byte[]	engineSign() Returns the signature bytes of all the data updated so far.
int	engineSign(byte[] outbuf, int offset, int len) Finishes this signature operation and stores the resulting signature bytes in the provided buffer outbuf, starting at offset.
abstract void	engineUpdate(byte[] b, int off, int len) Updates the data to be signed or verified, using the specified array of bytes, starting at the specified offset.
void	engineUpdate(ByteBuffer input) Updates the data to be signed or verified using the specified ByteBuffer.
abstract void	engineUpdate(byte b) Updates the data to be signed or verified using the specified byte.
boolean	engineVerify(byte[] sigBytes, int offset, int length) Verifies the passed-in signature in the specified array of bytes, starting at the specified offset.
abstract boolean	engineVerify(byte[] sigBytes) Verifies the passed-in signature.

From class java.lang.Object

Object	clone() Creates and returns a copy of this Object.
boolean	equals(Object obj) Compares this instance with the specified object and indicates if they are equal.
void	finalize() Invoked when the garbage collector has detected that this instance is no longer reachable.
final Class<?>	getClass() Returns the unique instance of Class that represents this object's class.
int	hashCode() Returns an integer hash code for this object.
final void	notify() Causes a thread which is waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
final void	notifyAll() Causes all threads which are waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
String	toString() Returns a string containing a concise, human-readable description of this object.
final void	wait(long timeout, int nanos) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait(long timeout) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait() Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object.

Constants

protected static final int SIGN

Possible state value, signifying that this signature object has been initialized for signing.

Constant Value: 2

protected static final int UNINITIALIZED

Possible state value, signifying that this signature object has not yet been initialized.

Constant Value: 0

protected static final int VERIFY

Possible state value, signifying that this signature object has been initialized for verification.

Constant Value: 3

Fields

protected int state

Current state of this signature object.

Protected Constructors

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 Cryptography Architecture Standard Algorithm Name Documentation for information about standard algorithm names.

Public Methods

public Object clone ()

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.

public final String getAlgorithm ()

Returns the name of the algorithm for this signature object.

Returns

• the name of the algorithm for this signature object.

public static Signature getInstance (String algorithm)

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.

Parameters

algorithm	the standard name of the algorithm requested. See the Signature section in the Java Cryptography Architecture Standard Algorithm Name Documentation for information about standard algorithm names.

Returns

• the new Signature object.

Throws

NoSuchAlgorithmException	if no Provider supports a Signature implementation for the specified algorithm.

See Also

• Provider

public static Signature getInstance (String algorithm, String provider)

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 Cryptography Architecture Standard Algorithm Name Documentation for information about standard algorithm names.
provider	the name of the provider.

Returns

• the new Signature object.

Throws

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.
IllegalArgumentException	if the provider name is null or empty.

See Also

• Provider

public static Signature getInstance (String algorithm, Provider provider)

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.

Parameters

algorithm	the name of the algorithm requested. See the Signature section in the Java Cryptography Architecture Standard Algorithm Name Documentation for information about standard algorithm names.
provider	the provider.

Returns

• the new Signature object.

Throws

NoSuchAlgorithmException	if a SignatureSpi implementation for the specified algorithm is not available from the specified Provider object.
IllegalArgumentException	if the provider is null.

See Also

• Provider

public final Object getParameter (String param)

This method is deprecated.
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.

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

• setParameter(String, Object)

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.

Returns

• the parameters used with this signature, or null if this signature does not use any parameters.

See Also

• setParameter(AlgorithmParameterSpec)

public final Provider getProvider ()

Returns the provider of this signature object.

Returns

• the provider of this signature object

public final void initSign (PrivateKey privateKey, SecureRandom random)

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.

Throws

InvalidKeyException	if the key is invalid.

public final void initSign (PrivateKey privateKey)

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.

public final void initVerify (PublicKey publicKey)

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.

public final 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.

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.

public final void setParameter (AlgorithmParameterSpec params)

Initializes this signature engine with the specified parameter set.

Parameters

params	the parameters

Throws

InvalidAlgorithmParameterException	if the given parameters are inappropriate for this signature engine

See Also

• getParameters()

public final void setParameter (String param, Object value)

This method is 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.

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.

See Also

• getParameter(String)

public 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. 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.

public final byte[] 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 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.

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.

public final void update (byte[] data)

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.

public 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.

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.

public final void update (ByteBuffer data)

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.

Parameters

data	the ByteBuffer

Throws

SignatureException	if this signature object is not initialized properly.

public final void update (byte b)

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.

public 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.

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.

public final 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). 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.