Package java.security

Class MessageDigest

java.lang.Object
java.security.MessageDigestSpi
java.security.MessageDigest
Direct Known Subclasses:
BCMessageDigest, OpenSSLMessageDigestJDK
public abstract class MessageDigest
extends MessageDigestSpi
Uses a one-way hash function to turn an arbitrary number of bytes into a fixed-length byte sequence. The original arbitrary-length sequence is the message, and the fixed-length byte sequence is the digest or message digest.

Sample Code

The basic pattern to digest an InputStream looks like this: 

  MessageDigest digester = MessageDigest.getInstance("MD5");
  byte[] bytes = new byte[8192];
  int byteCount;
  while ((byteCount = in.read(bytes)) > 0) {
    digester.update(bytes, 0, byteCount);
  }
  byte[] digest = digester.digest();

That is, after creating or resetting a MessageDigest you should call update(byte[],int,int) for each block of input data, and then call digest() to get the final digest. Note that calling digest resets the MessageDigest. Advanced users who want partial digests should clone their MessageDigest before calling digest.

This class is not thread-safe.

See Also:
MessageDigestSpi

  • Constructor Summary

    Constructors
    Modifier Constructor Description
    protected MessageDigest​(String algorithm)
    Constructs a new instance of MessageDigest with the name of the algorithm to use.

  • Method Summary

    Modifier and Type Method Description
    Object clone()
    Creates and returns a copy of this Object.
    byte[] digest()
    Computes and returns the final hash value for this MessageDigest.
    byte[] digest​(byte[] input)
    Performs the final update and then computes and returns the final hash value for this MessageDigest.
    int digest​(byte[] buf, int offset, int len)
    Computes and stores the final hash value for this MessageDigest.
    String getAlgorithm()
    Returns the name of the algorithm of this MessageDigest.
    int getDigestLength()
    Returns the engine digest length in bytes.
    static MessageDigest getInstance​(String algorithm)
    Returns a new instance of MessageDigest that utilizes the specified algorithm.
    static MessageDigest getInstance​(String algorithm, String provider)
    Returns a new instance of MessageDigest that utilizes the specified algorithm from the specified provider.
    static MessageDigest getInstance​(String algorithm, Provider provider)
    Returns a new instance of MessageDigest that utilizes the specified algorithm from the specified provider.
    Provider getProvider()
    Returns the provider associated with this MessageDigest.
    static boolean isEqual​(byte[] digesta, byte[] digestb)
    Indicates whether to digest are equal by performing a simply byte-per-byte compare of the two digests.
    void reset()
    Puts this MessageDigest back in an initial state, such that it is ready to compute a one way hash value.
    String toString()
    Returns a string containing a concise, human-readable description of this MessageDigest including the name of its algorithm.
    void update​(byte arg0)
    Updates this MessageDigest using the given byte.
    void update​(byte[] input)
    Updates this MessageDigest using the given byte[].
    void update​(byte[] input, int offset, int len)
    Updates this MessageDigest using the given byte[].
    void update​(ByteBuffer input)
    Updates this MessageDigest using the given input.

    Methods inherited from class java.security.MessageDigestSpi

    engineDigest, engineDigest, engineGetDigestLength, engineReset, engineUpdate, engineUpdate, engineUpdate

    Methods inherited from class java.lang.Object

    equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

  • Constructor Details

    • MessageDigest

      protected MessageDigest​(String algorithm)
      Constructs a new instance of MessageDigest with the name of the algorithm to use.
      Parameters:
      algorithm - the name of algorithm to use

  • Method Details

    • getInstance

      public static MessageDigest getInstance​(String algorithm) throws NoSuchAlgorithmException
      Returns a new instance of MessageDigest that utilizes the specified algorithm.
      Parameters:
      algorithm - the name of the algorithm to use
      Returns:
      a new instance of MessageDigest that utilizes the specified algorithm
      Throws:
      NoSuchAlgorithmException - if the specified algorithm is not available
      NullPointerException - if algorithm is null

    • getInstance

      public static MessageDigest getInstance​(String algorithm, String provider) throws NoSuchAlgorithmException, NoSuchProviderException
      Returns a new instance of MessageDigest that utilizes the specified algorithm from the specified provider.
      Parameters:
      algorithm - the name of the algorithm to use
      provider - the name of the provider
      Returns:
      a new instance of MessageDigest that utilizes the specified algorithm from the specified provider
      Throws:
      NoSuchAlgorithmException - if the specified algorithm is not available
      NoSuchProviderException - if the specified provider is not available
      NullPointerException - if algorithm is null
      IllegalArgumentException - if provider == null || provider.isEmpty()

    • getInstance

      public static MessageDigest getInstance​(String algorithm, Provider provider) throws NoSuchAlgorithmException
      Returns a new instance of MessageDigest that utilizes the specified algorithm from the specified provider.
      Parameters:
      algorithm - the name of the algorithm to use
      provider - the provider
      Returns:
      a new instance of MessageDigest that utilizes the specified algorithm from the specified provider
      Throws:
      NoSuchAlgorithmException - if the specified algorithm is not available
      NullPointerException - if algorithm is null
      IllegalArgumentException - if provider == null

    • reset

      public void reset()
      Puts this MessageDigest back in an initial state, such that it is ready to compute a one way hash value.

    • update

      public void update​(byte arg0)
      Updates this MessageDigest using the given byte.
      Parameters:
      arg0 - the byte to update this MessageDigest with
      See Also:
      reset()

    • update

      public void update​(byte[] input, int offset, int len)
      Updates this MessageDigest using the given byte[].
      Parameters:
      input - the byte array
      offset - the index of the first byte in input to update from
      len - the number of bytes in input to update from
      Throws:
      IllegalArgumentException - if offset or len are not valid in respect to input

    • update

      public void update​(byte[] input)
      Updates this MessageDigest using the given byte[].
      Parameters:
      input - the byte array
      Throws:
      NullPointerException - if input is null

    • digest

      public byte[] digest()
      Computes and returns the final hash value for this MessageDigest. After the digest is computed the receiver is reset.
      Returns:
      the computed one way hash value
      See Also:
      reset()

    • digest

      public int digest​(byte[] buf, int offset, int len) throws DigestException
      Computes and stores the final hash value for this MessageDigest. After the digest is computed the receiver is reset.
      Parameters:
      buf - the buffer to store the result
      offset - the index of the first byte in buf to store
      len - the number of bytes allocated for the digest
      Returns:
      the number of bytes written to buf
      Throws:
      DigestException - if an error occurs
      IllegalArgumentException - if offset or len are not valid in respect to buf
      See Also:
      reset()

    • digest

      public byte[] digest​(byte[] input)
      Performs the final update and then computes and returns the final hash value for this MessageDigest. After the digest is computed the receiver is reset.
      Parameters:
      input - the byte array
      Returns:
      the computed one way hash value
      See Also:
      reset()

    • toString

      public String toString()
      Returns a string containing a concise, human-readable description of this MessageDigest including the name of its algorithm.
      Overrides:
      toString in class Object
      Returns:
      a printable representation for this MessageDigest

    • isEqual

      public static boolean isEqual​(byte[] digesta, byte[] digestb)
      Indicates whether to digest are equal by performing a simply byte-per-byte compare of the two digests.
      Parameters:
      digesta - the first digest to be compared
      digestb - the second digest to be compared
      Returns:
      true if the two hashes are equal, false otherwise

    • getAlgorithm

      public final String getAlgorithm()
      Returns the name of the algorithm of this MessageDigest.
      Returns:
      the name of the algorithm of this MessageDigest

    • getProvider

      public final Provider getProvider()
      Returns the provider associated with this MessageDigest.
      Returns:
      the provider associated with this MessageDigest

    • getDigestLength

      public final int getDigestLength()
      Returns the engine digest length in bytes. If the implementation does not implement this function or is not an instance of Cloneable, 0 is returned.
      Returns:
      the digest length in bytes, or 0

    • clone

      public Object clone() throws CloneNotSupportedException
      Description copied from class: Object
      Creates and returns a copy of this Object. The default implementation returns a so-called "shallow" copy: It creates a new instance of the same class and then copies the field values (including object references) from this instance to the new instance. A "deep" copy, in contrast, would also recursively clone nested objects. A subclass that needs to implement this kind of cloning should call super.clone() to create the new instance and then create deep copies of the nested, mutable objects.
      Overrides:
      clone in class MessageDigestSpi
      Returns:
      a copy of this object.
      Throws:
      CloneNotSupportedException - if this object's class does not implement the Cloneable interface.

    • update

      public final void update​(ByteBuffer input)
      Updates this MessageDigest using the given input.
      Parameters:
      input - the ByteBuffer