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-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.
Every implementation of the Java platform is required to support the following standard Signature algorithms:
- SHA1withDSA
- SHA1withRSA
- SHA256withRSA
These algorithms are described in the Signature section of the Java Cryptography Architecture Standard Algorithm Name Documentation. Consult the release documentation for your implementation to see if any other algorithms are supported.

Field Summary

Fields
Modifier and Type	Field and Description
`protected static 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 int`	`UNINITIALIZED` Possible `state` value, signifying that this signature object has not yet been initialized.
`protected static int`	`VERIFY` Possible `state` value, signifying that this signature object has been initialized for verification.

Fields inherited from class java.security.SignatureSpi
appRandom

Constructor Summary

Constructors
Modifier Constructor and Description

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

Constructors
Modifier	Constructor and Description
`protected`	`Signature(java.lang.String algorithm)` Creates a Signature object for the specified algorithm.

Method Summary

All Methods Static Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`java.lang.Object`	`clone()` Returns a clone if the implementation is cloneable.
`java.lang.String`	`getAlgorithm()` Returns the name of the algorithm for this signature object.
`static Signature`	`getInstance(java.lang.String algorithm)` Returns a Signature object that implements the specified signature algorithm.
`static Signature`	`getInstance(java.lang.String algorithm, java.lang.String provider)` Returns a Signature object that implements the specified signature algorithm.
`void`	`initSign(PrivateKey privateKey)` Initialize this object for signing.
`void`	`initSign(PrivateKey privateKey, SecureRandom random)` Initialize this object for signing.
`void`	`initVerify(Certificate certificate)` Initializes this object for verification, using the public key from the given certificate.
`void`	`initVerify(PublicKey publicKey)` Initializes this object for verification.
`void`	`setParameter(AlgorithmParameterSpec params)` Initializes this signature engine with the specified parameter set.
`byte[]`	`sign()` Returns the signature bytes of all the data updated.
`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`.
`java.lang.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.
`void`	`update(byte b)` Updates the data to be signed or verified by a byte.
`void`	`update(byte[] data)` Updates the data to be signed or verified, using the specified array of bytes.
`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.
`boolean`	`verify(byte[] signature)` Verifies the passed-in signature.
`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 inherited from class java.security.SignatureSpi
engineInitSign, engineInitSign, engineInitVerify, engineSetParameter, engineSign, engineSign, engineUpdate, engineUpdate, engineVerify, engineVerify

Methods inherited from class java.lang.Object
equals, getClass, hashCode, notify, notifyAll, wait, wait, wait

- Field Detail
  - UNINITIALIZED
```
protected static final int UNINITIALIZED
```
    Possible state value, signifying that this signature object has not yet been initialized.
    
    See Also:
    
    Constant Field Values
  - SIGN
```
protected static final int SIGN
```
    Possible state value, signifying that this signature object has been initialized for signing.
    
    See Also:
    
    Constant Field Values
  - VERIFY
```
protected static final int VERIFY
```
    Possible state value, signifying that this signature object has been initialized for verification.
    
    See Also:
    
    Constant Field Values
  - state
```
protected int state
```
    Current state of this signature object.
- Constructor Detail
  - Signature
```
protected Signature(java.lang.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.
- Method Detail
  - getInstance
```
public static Signature getInstance(java.lang.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.
    
    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.
  - getInstance
```
public static Signature getInstance(java.lang.String algorithm,
                                    java.lang.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.
    
    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.
    
    java.lang.IllegalArgumentException - if the provider name is null or empty.
  - 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.
    
    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.
    
    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.
    
    java.lang.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.
  - getAlgorithm
```
public final java.lang.String getAlgorithm()
```
    Returns the name of the algorithm for this signature object.
    
    Returns:
    
    the name of the algorithm for this signature object.
  - toString
```
public java.lang.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 java.lang.Object
    
    Returns:
    
    a string representation of this signature object.
  - setParameter
```
public final void setParameter(AlgorithmParameterSpec params)
                        throws InvalidAlgorithmParameterException
```
    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
  - clone
```
public java.lang.Object clone()
                       throws java.lang.CloneNotSupportedException
```
    Returns a clone if the implementation is cloneable.
    
    Overrides:
    
    clone in class SignatureSpi
    
    Returns:
    
    a clone if the implementation is cloneable.
    
    Throws:
    
    java.lang.CloneNotSupportedException - if this is called on an implementation that does not support Cloneable.

Class Signature

Field Summary

Fields inherited from class java.security.SignatureSpi

Constructor Summary

Method Summary

Methods inherited from class java.security.SignatureSpi

Methods inherited from class java.lang.Object

Field Detail

UNINITIALIZED

SIGN

VERIFY

state

Constructor Detail

Signature

Method Detail

getInstance

getInstance

initVerify

initVerify

initSign

initSign

sign

sign

verify

verify

update

update

update

getAlgorithm

toString

setParameter

clone