A MAC provides a way to check * the integrity of information transmitted over or stored in an unreliable * medium, based on a secret key. Typically, message * authentication codes are used between two parties that share a secret * key in order to validate information transmitted between these * parties. * *
A MAC mechanism that is based on cryptographic hash functions is * referred to as HMAC. HMAC can be used with any cryptographic hash function, * e.g., MD5 or SHA-1, in combination with a secret shared key. HMAC is * specified in RFC 2104. * *
Android provides the following Mac algorithms
*
| Name | *Supported (API Levels) | *
|---|---|
| DESedeMAC | *1–8 | *
| DESedeMAC/CFB8 | *1–8 | *
| DESedeMAC64 | *1–8 | *
| DESMAC | *1–8 | *
| DESMAC/CFB8 | *1–8 | *
| DESwithISO9797 | *1–8 | *
| HmacMD5 | *1+ | *
| HmacSHA1 | *1+ | *
| HmacSHA224 | *1–8, 22+ | *
| HmacSHA256 | *1+ | *
| HmacSHA384 | *1+ | *
| HmacSHA512 | *1+ | *
| ISO9797ALG3MAC | *1–8 | *
| PBEwithHmacSHA | *1+ | *
| PBEwithHmacSHA1 | *1+ | *
Mac object.
*
* This is the same name that was specified in one of the
* getInstance calls that created this
* Mac object.
*
* @return the algorithm name of this Mac object.
*/
public final String getAlgorithm() {
return this.algorithm;
}
/**
* Returns a Mac object that implements the
* specified MAC algorithm.
*
*
This method traverses the list of registered security Providers, * starting with the most preferred Provider. * A new Mac object encapsulating the * MacSpi 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 requested MAC algorithm.
* See the Mac section in the
* Java Cryptography Architecture Standard Algorithm Name Documentation
* for information about standard algorithm names.
*
* @return the new Mac object.
*
* @exception NoSuchAlgorithmException if no Provider supports a
* MacSpi implementation for the
* specified algorithm.
*
* @see java.security.Provider
*/
public static final Mac getInstance(String algorithm)
throws NoSuchAlgorithmException {
List services = GetInstance.getServices("Mac", algorithm);
// make sure there is at least one service from a signed provider
Iterator t = services.iterator();
while (t.hasNext()) {
Service s = (Service)t.next();
if (JceSecurity.canUseProvider(s.getProvider()) == false) {
continue;
}
return new Mac(algorithm);
}
throw new NoSuchAlgorithmException
("Algorithm " + algorithm + " not available");
}
/**
* Returns a Mac object that implements the
* specified MAC algorithm.
*
*
A new Mac object encapsulating the * MacSpi 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 standard name of the requested MAC algorithm.
* See the Mac 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 Mac object.
*
* @exception NoSuchAlgorithmException if a MacSpi
* 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
* is null or empty.
*
* @see java.security.Provider
*/
public static final Mac getInstance(String algorithm, String provider)
throws NoSuchAlgorithmException, NoSuchProviderException {
Instance instance = JceSecurity.getInstance
("Mac", MacSpi.class, algorithm, provider);
return new Mac((MacSpi)instance.impl, instance.provider, algorithm);
}
/**
* Returns a Mac object that implements the
* specified MAC algorithm.
*
*
A new Mac object encapsulating the
* MacSpi 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 standard name of the requested MAC algorithm.
* See the Mac section in the
* Java Cryptography Architecture Standard Algorithm Name Documentation
* for information about standard algorithm names.
*
* @param provider the provider.
*
* @return the new Mac object.
*
* @exception NoSuchAlgorithmException if a MacSpi
* implementation for the specified algorithm is not available
* from the specified Provider object.
*
* @exception IllegalArgumentException if the provider
* is null.
*
* @see java.security.Provider
*/
public static final Mac getInstance(String algorithm, Provider provider)
throws NoSuchAlgorithmException {
Instance instance = JceSecurity.getInstance
("Mac", MacSpi.class, algorithm, provider);
return new Mac((MacSpi)instance.impl, instance.provider, algorithm);
}
// 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 init()
* is not the first method called.
*/
void chooseFirstProvider() {
if (spi != null || lock == null) {
return;
}
synchronized (lock) {
if (spi != null) {
return;
}
if (debug != null) {
int w = --warnCount;
if (w >= 0) {
debug.println("Mac.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;
for (Service s : GetInstance.getServices("Mac", algorithm)) {
if (JceSecurity.canUseProvider(s.getProvider()) == false) {
continue;
}
try {
Object obj = s.newInstance(null);
if (obj instanceof MacSpi == false) {
continue;
}
spi = (MacSpi)obj;
provider = s.getProvider();
return;
} catch (NoSuchAlgorithmException e) {
lastException = e;
}
}
ProviderException e = new ProviderException
("Could not construct MacSpi instance");
if (lastException != null) {
e.initCause(lastException);
}
throw e;
}
}
private void chooseProvider(Key key, AlgorithmParameterSpec params)
throws InvalidKeyException, InvalidAlgorithmParameterException {
synchronized (lock) {
if (spi != null && (key == null || lock == null)) {
spi.engineInit(key, params);
return;
}
Exception lastException = null;
for (Service s : GetInstance.getServices("Mac", algorithm)) {
// if provider says it does not support this key, ignore it
if (s.supportsParameter(key) == false) {
continue;
}
if (JceSecurity.canUseProvider(s.getProvider()) == false) {
continue;
}
try {
MacSpi spi = (MacSpi)s.newInstance(null);
spi.engineInit(key, params);
provider = s.getProvider();
this.spi = spi;
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 InvalidAlgorithmParameterException) {
throw (InvalidAlgorithmParameterException)lastException;
}
if (lastException instanceof RuntimeException) {
throw (RuntimeException)lastException;
}
String kName = (key != null) ? key.getClass().getName() : "(null)";
throw new InvalidKeyException
("No installed provider supports this key: "
+ kName, lastException);
}
}
/**
* Returns the provider of this Mac object.
*
* @return the provider of this Mac object.
*/
public final Provider getProvider() {
chooseFirstProvider();
return this.provider;
}
/**
* Returns the length of the MAC in bytes.
*
* @return the MAC length in bytes.
*/
public final int getMacLength() {
chooseFirstProvider();
return spi.engineGetMacLength();
}
/**
* Initializes this Mac object with the given key.
*
* @param key the key.
*
* @exception InvalidKeyException if the given key is inappropriate for
* initializing this MAC.
*/
public final void init(Key key) throws InvalidKeyException {
try {
if (spi != null && (key == null || lock == null)) {
spi.engineInit(key, null);
} else {
chooseProvider(key, null);
}
} catch (InvalidAlgorithmParameterException e) {
throw new InvalidKeyException("init() failed", e);
}
initialized = true;
}
/**
* Initializes this Mac object with the given key and
* algorithm parameters.
*
* @param key the key.
* @param params the algorithm parameters.
*
* @exception InvalidKeyException if the given key is inappropriate for
* initializing this MAC.
* @exception InvalidAlgorithmParameterException if the given algorithm
* parameters are inappropriate for this MAC.
*/
public final void init(Key key, AlgorithmParameterSpec params)
throws InvalidKeyException, InvalidAlgorithmParameterException {
if (spi != null && (key == null || lock == null)) {
spi.engineInit(key, params);
} else {
chooseProvider(key, params);
}
initialized = true;
}
/**
* Processes the given byte.
*
* @param input the input byte to be processed.
*
* @exception IllegalStateException if this Mac has not been
* initialized.
*/
public final void update(byte input) throws IllegalStateException {
chooseFirstProvider();
if (initialized == false) {
throw new IllegalStateException("MAC not initialized");
}
spi.engineUpdate(input);
}
/**
* Processes the given array of bytes.
*
* @param input the array of bytes to be processed.
*
* @exception IllegalStateException if this Mac has not been
* initialized.
*/
public final void update(byte[] input) throws IllegalStateException {
chooseFirstProvider();
if (initialized == false) {
throw new IllegalStateException("MAC not initialized");
}
if (input != null) {
spi.engineUpdate(input, 0, input.length);
}
}
/**
* Processes the first len bytes in input,
* starting at offset inclusive.
*
* @param input the input buffer.
* @param offset the offset in input where the input starts.
* @param len the number of bytes to process.
*
* @exception IllegalStateException if this Mac has not been
* initialized.
*/
public final void update(byte[] input, int offset, int len)
throws IllegalStateException {
chooseFirstProvider();
if (initialized == false) {
throw new IllegalStateException("MAC not initialized");
}
if (input != null) {
if ((offset < 0) || (len > (input.length - offset)) || (len < 0))
throw new IllegalArgumentException("Bad arguments");
spi.engineUpdate(input, offset, len);
}
}
/**
* Processes input.remaining() bytes in the ByteBuffer
* input, starting at input.position().
* Upon return, the buffer's position will be equal to its limit;
* its limit will not have changed.
*
* @param input the ByteBuffer
*
* @exception IllegalStateException if this Mac has not been
* initialized.
* @since 1.5
*/
public final void update(ByteBuffer input) {
chooseFirstProvider();
if (initialized == false) {
throw new IllegalStateException("MAC not initialized");
}
if (input == null) {
throw new IllegalArgumentException("Buffer must not be null");
}
spi.engineUpdate(input);
}
/**
* Finishes the MAC operation.
*
*
A call to this method resets this Mac object to the
* state it was in when previously initialized via a call to
* init(Key) or
* init(Key, AlgorithmParameterSpec).
* That is, the object is reset and available to generate another MAC from
* the same key, if desired, via new calls to update and
* doFinal.
* (In order to reuse this Mac object with a different key,
* it must be reinitialized via a call to init(Key) or
* init(Key, AlgorithmParameterSpec).
*
* @return the MAC result.
*
* @exception IllegalStateException if this Mac has not been
* initialized.
*/
public final byte[] doFinal() throws IllegalStateException {
chooseFirstProvider();
if (initialized == false) {
throw new IllegalStateException("MAC not initialized");
}
byte[] mac = spi.engineDoFinal();
spi.engineReset();
return mac;
}
/**
* Finishes the MAC operation.
*
*
A call to this method resets this Mac object to the
* state it was in when previously initialized via a call to
* init(Key) or
* init(Key, AlgorithmParameterSpec).
* That is, the object is reset and available to generate another MAC from
* the same key, if desired, via new calls to update and
* doFinal.
* (In order to reuse this Mac object with a different key,
* it must be reinitialized via a call to init(Key) or
* init(Key, AlgorithmParameterSpec).
*
*
The MAC result is stored in output, starting at
* outOffset inclusive.
*
* @param output the buffer where the MAC result is stored
* @param outOffset the offset in output where the MAC is
* stored
*
* @exception ShortBufferException if the given output buffer is too small
* to hold the result
* @exception IllegalStateException if this Mac has not been
* initialized.
*/
public final void doFinal(byte[] output, int outOffset)
throws ShortBufferException, IllegalStateException
{
chooseFirstProvider();
if (initialized == false) {
throw new IllegalStateException("MAC not initialized");
}
int macLen = getMacLength();
if (output == null || output.length-outOffset < macLen) {
throw new ShortBufferException
("Cannot store MAC in output buffer");
}
byte[] mac = doFinal();
System.arraycopy(mac, 0, output, outOffset, macLen);
return;
}
/**
* Processes the given array of bytes and finishes the MAC operation.
*
*
A call to this method resets this Mac object to the
* state it was in when previously initialized via a call to
* init(Key) or
* init(Key, AlgorithmParameterSpec).
* That is, the object is reset and available to generate another MAC from
* the same key, if desired, via new calls to update and
* doFinal.
* (In order to reuse this Mac object with a different key,
* it must be reinitialized via a call to init(Key) or
* init(Key, AlgorithmParameterSpec).
*
* @param input data in bytes
* @return the MAC result.
*
* @exception IllegalStateException if this Mac has not been
* initialized.
*/
public final byte[] doFinal(byte[] input) throws IllegalStateException
{
chooseFirstProvider();
if (initialized == false) {
throw new IllegalStateException("MAC not initialized");
}
update(input);
return doFinal();
}
/**
* Resets this Mac object.
*
*
A call to this method resets this Mac object to the
* state it was in when previously initialized via a call to
* init(Key) or
* init(Key, AlgorithmParameterSpec).
* That is, the object is reset and available to generate another MAC from
* the same key, if desired, via new calls to update and
* doFinal.
* (In order to reuse this Mac object with a different key,
* it must be reinitialized via a call to init(Key) or
* init(Key, AlgorithmParameterSpec).
*/
public final void reset() {
chooseFirstProvider();
spi.engineReset();
}
/**
* Returns a clone if the provider implementation is cloneable.
*
* @return a clone if the provider implementation is cloneable.
*
* @exception CloneNotSupportedException if this is called on a
* delegate that does not support Cloneable.
*/
public final Object clone() throws CloneNotSupportedException {
chooseFirstProvider();
Mac that = (Mac)super.clone();
that.spi = (MacSpi)this.spi.clone();
return that;
}
/**
* Returns the {@code MacSpi} backing this {@code Mac} or {@code null} if no {@code MacSpi} is
* backing this {@code Mac}.
*
* @hide
*/
public MacSpi getCurrentSpi() {
return spi;
}
}