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:
* *
* *
Depending on the type of initialization, this will update the * bytes to be signed or verified. See the * {@link #update(byte) update} methods.
* *
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:
*
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 {@link Security#getProviders() Security.getProviders()} method.
*
* @param 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.
*
* @return the new Signature object.
*
* @exception NoSuchAlgorithmException if no Provider supports a
* Signature implementation for the
* specified algorithm.
*
* @see Provider
*/
public static Signature getInstance(String algorithm)
throws NoSuchAlgorithmException {
List 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 {@link Security#getProviders() Security.getProviders()} method.
*
* @param 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.
*
* @param provider the name of the provider.
*
* @return the new Signature object.
*
* @exception NoSuchAlgorithmException if a SignatureSpi
* implementation for the specified algorithm is not
* available from the specified provider.
*
* @exception NoSuchProviderException if the specified provider is not
* registered in the security provider list.
*
* @exception IllegalArgumentException if the provider name is null
* or empty.
*
* @see Provider
*/
public static Signature getInstance(String algorithm, String provider)
throws NoSuchAlgorithmException, NoSuchProviderException {
if (algorithm.equalsIgnoreCase(RSA_SIGNATURE)) {
// exception compatibility with existing code
if ((provider == null) || (provider.length() == 0)) {
throw new IllegalArgumentException("missing provider");
}
Provider p = Security.getProvider(provider);
if (p == null) {
throw new NoSuchProviderException
("no such provider: " + provider);
}
return getInstanceRSA(p);
}
Instance instance = GetInstance.getInstance
("Signature", SignatureSpi.class, algorithm, provider);
return getInstance(instance, algorithm);
}
/**
* 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.
*
* @param 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.
*
* @param provider the provider.
*
* @return the new Signature object.
*
* @exception NoSuchAlgorithmException if a SignatureSpi
* implementation for the specified algorithm is not available
* from the specified Provider object.
*
* @exception IllegalArgumentException if the provider is null.
*
* @see Provider
*
* @since 1.4
*/
public static Signature getInstance(String algorithm, Provider provider)
throws NoSuchAlgorithmException {
if (algorithm.equalsIgnoreCase(RSA_SIGNATURE)) {
// exception compatibility with existing code
if (provider == null) {
throw new IllegalArgumentException("missing provider");
}
return getInstanceRSA(provider);
}
Instance instance = GetInstance.getInstance
("Signature", SignatureSpi.class, algorithm, provider);
return getInstance(instance, algorithm);
}
// return an implementation for NONEwithRSA, which is a special case
// because of the Cipher.RSA/ECB/PKCS1Padding compatibility wrapper
private static Signature getInstanceRSA(Provider p)
throws NoSuchAlgorithmException {
// try Signature first
Service s = p.getService("Signature", RSA_SIGNATURE);
if (s != null) {
Instance instance = GetInstance.getInstance(s, SignatureSpi.class);
return getInstance(instance, RSA_SIGNATURE);
}
// check Cipher
try {
Cipher c = Cipher.getInstance(RSA_CIPHER, p);
return new Delegate(new CipherAdapter(c), RSA_SIGNATURE);
} catch (GeneralSecurityException e) {
// throw Signature style exception message to avoid confusion,
// but append Cipher exception as cause
throw new NoSuchAlgorithmException("no such algorithm: "
+ RSA_SIGNATURE + " for provider " + p.getName(), e);
}
}
/**
* Returns the provider of this signature object.
*
* @return the provider of this signature object
*/
public final Provider getProvider() {
chooseFirstProvider();
return this.provider;
}
void chooseFirstProvider() {
// empty, overridden in Delegate
}
/**
* Initializes this object for verification. If this method is called
* again with a different argument, it negates the effect
* of this call.
*
* @param publicKey the public key of the identity whose signature is
* going to be verified.
*
* @exception InvalidKeyException if the key is invalid.
*/
public final void initVerify(PublicKey publicKey)
throws InvalidKeyException {
engineInitVerify(publicKey);
state = VERIFY;
}
/**
* 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
* A call to this method resets this signature object to the state
* it was in when previously initialized for signing via a
* call to This signature object is reset to its initial state (the state it
* was in after a call to one of the A call to this method resets this signature object to the state
* it was in when previously initialized for verification via a
* call to A call to this method resets this signature object to the state
* it was in when previously initialized for verification via a
* call to 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.
*
* @return the parameters used with this signature, or null if this
* signature does not use any parameters.
*
* @see #setParameter(AlgorithmParameterSpec)
* @since 1.4
*/
public final AlgorithmParameters getParameters() {
return engineGetParameters();
}
/**
* 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.
*
* @param param the string name of the parameter.
*
* @return the object that represents the parameter value, or null if
* there is none.
*
* @exception InvalidParameterException if InvalidKeyException is thrown.
*
* @param certificate the certificate of the identity whose signature is
* going to be verified.
*
* @exception 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
*/
public final void initVerify(Certificate certificate)
throws InvalidKeyException {
// If the certificate is of type X509Certificate,
// we should check whether it has a Key Usage
// extension marked as critical.
if (certificate instanceof java.security.cert.X509Certificate) {
// Check whether the cert has a key usage extension
// marked as a critical extension.
// The OID for KeyUsage extension is 2.5.29.15.
X509Certificate cert = (X509Certificate)certificate;
SetinitSign(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.
*
* @return the signature bytes of the signing operation's result.
*
* @exception SignatureException if this signature object is not
* initialized properly or if this signature algorithm is unable to
* process the input data provided.
*/
public final byte[] sign() throws SignatureException {
if (state == SIGN) {
return engineSign();
}
throw new SignatureException("object not initialized for " +
"signing");
}
/**
* 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.
*
* initSign methods) and
* can be reused to generate further signatures with the same private key.
*
* @param outbuf buffer for the signature result.
*
* @param offset offset into outbuf where the signature is
* stored.
*
* @param len number of bytes within outbuf allotted for the
* signature.
*
* @return the number of bytes placed into outbuf.
*
* @exception 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
*/
public final int sign(byte[] outbuf, int offset, int len)
throws SignatureException {
if (outbuf == null) {
throw new IllegalArgumentException("No output buffer given");
}
if (outbuf.length - offset < len) {
throw new IllegalArgumentException
("Output buffer too small for specified offset and length");
}
if (state != SIGN) {
throw new SignatureException("object not initialized for " +
"signing");
}
return engineSign(outbuf, offset, len);
}
/**
* Verifies the passed-in signature.
*
* 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.
*
* @param signature the signature bytes to be verified.
*
* @return true if the signature was verified, false if not.
*
* @exception 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.
*/
public final boolean verify(byte[] signature) throws SignatureException {
if (state == VERIFY) {
return engineVerify(signature);
}
throw new SignatureException("object not initialized for " +
"verification");
}
/**
* Verifies the passed-in signature in the specified array
* of bytes, starting at the specified offset.
*
* 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.
*
*
* @param signature the signature bytes to be verified.
* @param offset the offset to start from in the array of bytes.
* @param length the number of bytes to use, starting at offset.
*
* @return true if the signature was verified, false if not.
*
* @exception 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.
* @exception 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
*/
public final boolean verify(byte[] signature, int offset, int length)
throws SignatureException {
if (state == VERIFY) {
if ((signature == null) || (offset < 0) || (length < 0) ||
(offset + length > signature.length)) {
throw new IllegalArgumentException("Bad arguments");
}
return engineVerify(signature, offset, length);
}
throw new SignatureException("object not initialized for " +
"verification");
}
/**
* Updates the data to be signed or verified by a byte.
*
* @param b the byte to use for the update.
*
* @exception SignatureException if this signature object is not
* initialized properly.
*/
public final void update(byte b) throws SignatureException {
if (state == VERIFY || state == SIGN) {
engineUpdate(b);
} else {
throw new SignatureException("object not initialized for "
+ "signature or verification");
}
}
/**
* Updates the data to be signed or verified, using the specified
* array of bytes.
*
* @param data the byte array to use for the update.
*
* @exception SignatureException if this signature object is not
* initialized properly.
*/
public final void update(byte[] data) throws SignatureException {
update(data, 0, data.length);
}
/**
* Updates the data to be signed or verified, using the specified
* array of bytes, starting at the specified offset.
*
* @param data the array of bytes.
* @param off the offset to start from in the array of bytes.
* @param len the number of bytes to use, starting at offset.
*
* @exception SignatureException if this signature object is not
* initialized properly.
*/
public final void update(byte[] data, int off, int len)
throws SignatureException {
if (state == SIGN || state == VERIFY) {
engineUpdate(data, off, len);
} else {
throw new SignatureException("object not initialized for "
+ "signature or verification");
}
}
/**
* 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.
*
* @param data the ByteBuffer
*
* @exception SignatureException if this signature object is not
* initialized properly.
* @since 1.5
*/
public final void update(ByteBuffer data) throws SignatureException {
if ((state != SIGN) && (state != VERIFY)) {
throw new SignatureException("object not initialized for "
+ "signature or verification");
}
if (data == null) {
throw new NullPointerException();
}
engineUpdate(data);
}
/**
* Returns the name of the algorithm for this signature object.
*
* @return the name of the algorithm for this signature object.
*/
public final String getAlgorithm() {
return this.algorithm;
}
/**
* Returns a string representation of this signature object,
* providing information that includes the state of the object
* and the name of the algorithm used.
*
* @return a string representation of this signature object.
*/
public String toString() {
String initState = "";
switch (state) {
case UNINITIALIZED:
initState = "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 #getParameter
*
* @deprecated Use
* {@link #setParameter(java.security.spec.AlgorithmParameterSpec)
* setParameter}.
*/
@Deprecated
public final void setParameter(String param, Object value)
throws InvalidParameterException {
engineSetParameter(param, value);
}
/**
* Initializes this signature engine with the specified parameter set.
*
* @param params the parameters
*
* @exception InvalidAlgorithmParameterException if the given parameters
* are inappropriate for this signature engine
*
* @see #getParameters
*/
public final void setParameter(AlgorithmParameterSpec params)
throws InvalidAlgorithmParameterException {
engineSetParameter(params);
}
/**
* Returns the parameters used with this signature object.
*
* param is an invalid
* parameter for this engine, or another exception occurs while
* trying to get this parameter.
*
* @see #setParameter(String, Object)
*
* @deprecated
*/
@Deprecated
public final Object getParameter(String param)
throws InvalidParameterException {
return engineGetParameter(param);
}
/**
* Returns a clone if the implementation is cloneable.
*
* @return a clone if the implementation is cloneable.
*
* @exception CloneNotSupportedException if this is called
* on an implementation that does not support Cloneable.
*/
public Object clone() throws CloneNotSupportedException {
if (this instanceof Cloneable) {
return super.clone();
} else {
throw new CloneNotSupportedException();
}
}
/*
* The following class allows providers to extend from SignatureSpi
* rather than from Signature. It represents a Signature with an
* encapsulated, provider-supplied SPI object (of type SignatureSpi).
* If the provider implementation is an instance of SignatureSpi, the
* getInstance() methods above return an instance of this class, with
* the SPI object encapsulated.
*
* Note: All SPI methods from the original Signature class have been
* moved up the hierarchy into a new class (SignatureSpi), which has
* been interposed in the hierarchy between the API (Signature)
* and its original parent (Object).
*/
private static class Delegate extends Signature {
// The provider implementation (delegate)
// filled in once the provider is selected
private SignatureSpi sigSpi;
// lock for mutex during provider selection
private final Object lock;
// next service to try in provider selection
// null once provider is selected
private Service firstService;
// remaining services to try in provider selection
// null once provider is selected
private IteratorCloneable.
*/
public Object clone() throws CloneNotSupportedException {
chooseFirstProvider();
if (sigSpi instanceof Cloneable) {
SignatureSpi sigSpiClone = (SignatureSpi)sigSpi.clone();
// Because 'algorithm' and 'provider' are private
// members of our supertype, we must perform a cast to
// access them.
Signature that =
new Delegate(sigSpiClone, ((Signature)this).algorithm);
that.provider = ((Signature)this).provider;
return that;
} else {
throw new CloneNotSupportedException();
}
}
private static SignatureSpi newInstance(Service s)
throws NoSuchAlgorithmException {
if (s.getType().equals("Cipher")) {
// must be NONEwithRSA
try {
Cipher c = Cipher.getInstance(RSA_CIPHER, s.getProvider());
return new CipherAdapter(c);
} catch (NoSuchPaddingException e) {
throw new NoSuchAlgorithmException(e);
}
} else {
Object o = s.newInstance(null);
if (o instanceof SignatureSpi == false) {
throw new NoSuchAlgorithmException
("Not a SignatureSpi: " + o.getClass().getName());
}
return (SignatureSpi)o;
}
}
// max number of debug warnings to print from chooseFirstProvider()
private static int warnCount = 10;
/**
* Choose the Spi from the first provider available. Used if
* delayed provider selection is not possible because initSign()/
* initVerify() is not the first method called.
*/
void chooseFirstProvider() {
if (sigSpi != null) {
return;
}
synchronized (lock) {
if (sigSpi != null) {
return;
}
if (debug != null) {
int w = --warnCount;
if (w >= 0) {
debug.println("Signature.init() not first method "
+ "called, disabling delayed provider selection");
if (w == 0) {
debug.println("Further warnings of this type will "
+ "be suppressed");
}
new Exception("Call trace").printStackTrace();
}
}
Exception lastException = null;
while ((firstService != null) || serviceIterator.hasNext()) {
Service s;
if (firstService != null) {
s = firstService;
firstService = null;
} else {
s = serviceIterator.next();
}
if (isSpi(s) == false) {
continue;
}
try {
sigSpi = newInstance(s);
provider = s.getProvider();
// not needed any more
firstService = null;
serviceIterator = null;
return;
} catch (NoSuchAlgorithmException e) {
lastException = e;
}
}
ProviderException e = new ProviderException
("Could not construct SignatureSpi instance");
if (lastException != null) {
e.initCause(lastException);
}
throw e;
}
}
private void chooseProvider(int type, Key key, SecureRandom random)
throws InvalidKeyException {
synchronized (lock) {
if (sigSpi != null) {
init(sigSpi, type, key, random);
return;
}
Exception lastException = null;
while ((firstService != null) || serviceIterator.hasNext()) {
Service s;
if (firstService != null) {
s = firstService;
firstService = null;
} else {
s = serviceIterator.next();
}
// if provider says it does not support this key, ignore it
if (s.supportsParameter(key) == false) {
continue;
}
// if instance is not a SignatureSpi, ignore it
if (isSpi(s) == false) {
continue;
}
try {
SignatureSpi spi = newInstance(s);
init(spi, type, key, random);
provider = s.getProvider();
sigSpi = spi;
firstService = null;
serviceIterator = null;
return;
} catch (Exception e) {
// NoSuchAlgorithmException from newInstance()
// InvalidKeyException from init()
// RuntimeException (ProviderException) from init()
if (lastException == null) {
lastException = e;
}
}
}
// no working provider found, fail
if (lastException instanceof InvalidKeyException) {
throw (InvalidKeyException)lastException;
}
if (lastException instanceof RuntimeException) {
throw (RuntimeException)lastException;
}
String k = (key != null) ? key.getClass().getName() : "(null)";
throw new InvalidKeyException
("No installed provider supports this key: "
+ k, lastException);
}
}
private final static int I_PUB = 1;
private final static int I_PRIV = 2;
private final static int I_PRIV_SR = 3;
private void init(SignatureSpi spi, int type, Key key,
SecureRandom random) throws InvalidKeyException {
switch (type) {
case I_PUB:
spi.engineInitVerify((PublicKey)key);
break;
case I_PRIV:
spi.engineInitSign((PrivateKey)key);
break;
case I_PRIV_SR:
spi.engineInitSign((PrivateKey)key, random);
break;
default:
throw new AssertionError("Internal error: " + type);
}
}
protected void engineInitVerify(PublicKey publicKey)
throws InvalidKeyException {
if (sigSpi != null) {
sigSpi.engineInitVerify(publicKey);
} else {
chooseProvider(I_PUB, publicKey, null);
}
}
protected void engineInitSign(PrivateKey privateKey)
throws InvalidKeyException {
if (sigSpi != null) {
sigSpi.engineInitSign(privateKey);
} else {
chooseProvider(I_PRIV, privateKey, null);
}
}
protected void engineInitSign(PrivateKey privateKey, SecureRandom sr)
throws InvalidKeyException {
if (sigSpi != null) {
sigSpi.engineInitSign(privateKey, sr);
} else {
chooseProvider(I_PRIV_SR, privateKey, sr);
}
}
protected void engineUpdate(byte b) throws SignatureException {
chooseFirstProvider();
sigSpi.engineUpdate(b);
}
protected void engineUpdate(byte[] b, int off, int len)
throws SignatureException {
chooseFirstProvider();
sigSpi.engineUpdate(b, off, len);
}
protected void engineUpdate(ByteBuffer data) {
chooseFirstProvider();
sigSpi.engineUpdate(data);
}
protected byte[] engineSign() throws SignatureException {
chooseFirstProvider();
return sigSpi.engineSign();
}
protected int engineSign(byte[] outbuf, int offset, int len)
throws SignatureException {
chooseFirstProvider();
return sigSpi.engineSign(outbuf, offset, len);
}
protected boolean engineVerify(byte[] sigBytes)
throws SignatureException {
chooseFirstProvider();
return sigSpi.engineVerify(sigBytes);
}
protected boolean engineVerify(byte[] sigBytes, int offset, int length)
throws SignatureException {
chooseFirstProvider();
return sigSpi.engineVerify(sigBytes, offset, length);
}
protected void engineSetParameter(String param, Object value)
throws InvalidParameterException {
chooseFirstProvider();
sigSpi.engineSetParameter(param, value);
}
protected void engineSetParameter(AlgorithmParameterSpec params)
throws InvalidAlgorithmParameterException {
chooseFirstProvider();
sigSpi.engineSetParameter(params);
}
protected Object engineGetParameter(String param)
throws InvalidParameterException {
chooseFirstProvider();
return sigSpi.engineGetParameter(param);
}
protected AlgorithmParameters engineGetParameters() {
chooseFirstProvider();
return sigSpi.engineGetParameters();
}
}
// adapter for RSA/ECB/PKCS1Padding ciphers
private static class CipherAdapter extends SignatureSpi {
private final Cipher cipher;
private ByteArrayOutputStream data;
CipherAdapter(Cipher cipher) {
this.cipher = cipher;
}
protected void engineInitVerify(PublicKey publicKey)
throws InvalidKeyException {
cipher.init(Cipher.DECRYPT_MODE, publicKey);
if (data == null) {
data = new ByteArrayOutputStream(128);
} else {
data.reset();
}
}
protected void engineInitSign(PrivateKey privateKey)
throws InvalidKeyException {
cipher.init(Cipher.ENCRYPT_MODE, privateKey);
data = null;
}
protected void engineInitSign(PrivateKey privateKey,
SecureRandom random) throws InvalidKeyException {
cipher.init(Cipher.ENCRYPT_MODE, privateKey, random);
data = null;
}
protected void engineUpdate(byte b) throws SignatureException {
engineUpdate(new byte[] {b}, 0, 1);
}
protected void engineUpdate(byte[] b, int off, int len)
throws SignatureException {
if (data != null) {
data.write(b, off, len);
return;
}
byte[] out = cipher.update(b, off, len);
if ((out != null) && (out.length != 0)) {
throw new SignatureException
("Cipher unexpectedly returned data");
}
}
protected byte[] engineSign() throws SignatureException {
try {
return cipher.doFinal();
} catch (IllegalBlockSizeException e) {
throw new SignatureException("doFinal() failed", e);
} catch (BadPaddingException e) {
throw new SignatureException("doFinal() failed", e);
}
}
protected boolean engineVerify(byte[] sigBytes)
throws SignatureException {
try {
byte[] out = cipher.doFinal(sigBytes);
byte[] dataBytes = data.toByteArray();
data.reset();
return Arrays.equals(out, dataBytes);
} catch (BadPaddingException e) {
// e.g. wrong public key used
// return false rather than throwing exception
return false;
} catch (IllegalBlockSizeException e) {
throw new SignatureException("doFinal() failed", e);
}
}
protected void engineSetParameter(String param, Object value)
throws InvalidParameterException {
throw new InvalidParameterException("Parameters not supported");
}
protected Object engineGetParameter(String param)
throws InvalidParameterException {
throw new InvalidParameterException("Parameters not supported");
}
}
}