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

  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:

Name 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
SHA256withECDSA 11+
SHA256withRSA 1+
SHA384withECDSA 11+
SHA384withRSA 1+
SHA512withECDSA 11+
SHA512withRSA 1+
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

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 was 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 was 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

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

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

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

public final Object getParameter (String param)

This method was 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.

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.

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

public final void setParameter (String param, Object value)

This method was 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.

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.