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Java Standard Edition (SE)

Mac


javax.crypto

Class Mac

  • All Implemented Interfaces:
    Cloneable


    public class Mac
    extends Object
    implements Cloneable
    This class provides the functionality of a "Message Authentication Code" (MAC) algorithm.

    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.

    Every implementation of the Java platform is required to support the following standard Mac algorithms:

    • HmacMD5
    • HmacSHA1
    • HmacSHA256
    These algorithms are described in the Mac 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.
    Since:
    1.4
    • Constructor Detail

      • Mac

        protected Mac(MacSpi macSpi,
                      Provider provider,
                      String algorithm)
        Creates a MAC object.
        Parameters:
        macSpi - the delegate
        provider - the provider
        algorithm - the algorithm
    • Method Detail

      • getAlgorithm

        public final String getAlgorithm()
        Returns the algorithm name of this Mac object.

        This is the same name that was specified in one of the getInstance calls that created this Mac object.

        Returns:
        the algorithm name of this Mac object.
      • getInstance

        public static final Mac getInstance(String algorithm)
                                     throws NoSuchAlgorithmException
        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 Security.getProviders() method.

        Parameters:
        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.
        Returns:
        the new Mac object.
        Throws:
        NoSuchAlgorithmException - if no Provider supports a MacSpi implementation for the specified algorithm.
        See Also:
        Provider
      • getInstance

        public static final Mac getInstance(String algorithm,
                                            Provider provider)
                                     throws NoSuchAlgorithmException
        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.

        Parameters:
        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.
        provider - the provider.
        Returns:
        the new Mac object.
        Throws:
        NoSuchAlgorithmException - if a MacSpi implementation for the specified algorithm is not available from the specified Provider object.
        IllegalArgumentException - if the provider is null.
        See Also:
        Provider
      • getProvider

        public final Provider getProvider()
        Returns the provider of this Mac object.
        Returns:
        the provider of this Mac object.
      • getMacLength

        public final int getMacLength()
        Returns the length of the MAC in bytes.
        Returns:
        the MAC length in bytes.
      • init

        public final void init(Key key)
                        throws InvalidKeyException
        Initializes this Mac object with the given key.
        Parameters:
        key - the key.
        Throws:
        InvalidKeyException - if the given key is inappropriate for initializing this MAC.
      • update

        public final void update(byte input)
                          throws IllegalStateException
        Processes the given byte.
        Parameters:
        input - the input byte to be processed.
        Throws:
        IllegalStateException - if this Mac has not been initialized.
      • update

        public final void update(byte[] input)
                          throws IllegalStateException
        Processes the given array of bytes.
        Parameters:
        input - the array of bytes to be processed.
        Throws:
        IllegalStateException - if this Mac has not been initialized.
      • update

        public final void update(byte[] input,
                                 int offset,
                                 int len)
                          throws IllegalStateException
        Processes the first len bytes in input, starting at offset inclusive.
        Parameters:
        input - the input buffer.
        offset - the offset in input where the input starts.
        len - the number of bytes to process.
        Throws:
        IllegalStateException - if this Mac has not been initialized.
      • update

        public final void update(ByteBuffer input)
        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.
        Parameters:
        input - the ByteBuffer
        Throws:
        IllegalStateException - if this Mac has not been initialized.
        Since:
        1.5
      • doFinal

        public final byte[] doFinal()
                             throws IllegalStateException
        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).

        Returns:
        the MAC result.
        Throws:
        IllegalStateException - if this Mac has not been initialized.
      • doFinal

        public final void doFinal(byte[] output,
                                  int outOffset)
                           throws ShortBufferException,
                                  IllegalStateException
        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.

        Parameters:
        output - the buffer where the MAC result is stored
        outOffset - the offset in output where the MAC is stored
        Throws:
        ShortBufferException - if the given output buffer is too small to hold the result
        IllegalStateException - if this Mac has not been initialized.
      • doFinal

        public final byte[] doFinal(byte[] input)
                             throws IllegalStateException
        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).

        Parameters:
        input - data in bytes
        Returns:
        the MAC result.
        Throws:
        IllegalStateException - if this Mac has not been initialized.
      • reset

        public final void reset()
        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).



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