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package java.security;

import java.nio.ByteBuffer;

import sun.security.jca.JCAUtil;


This class defines the Service Provider Interface (SPI) for the MessageDigest class, which provides the functionality of a message digest algorithm, such as MD5 or SHA. Message digests are secure one-way hash functions that take arbitrary-sized data and output a fixed-length hash value. 
 All the abstract methods in this class must be implemented by a
cryptographic service provider who wishes to supply the implementation
of a particular message digest algorithm.

 Implementations are free to implement the Cloneable interface.

Author:Benjamin Renaud
See Also:
Since:1.2
/**
 * This class defines the <i>Service Provider Interface</i> (<b>SPI</b>)
 * for the {@code MessageDigest} class, which provides the functionality
 * of a message digest algorithm, such as MD5 or SHA. Message digests are
 * secure one-way hash functions that take arbitrary-sized data and output a
 * fixed-length hash value.
 *
 * <p> All the abstract methods in this class must be implemented by a
 * cryptographic service provider who wishes to supply the implementation
 * of a particular message digest algorithm.
 *
 * <p> Implementations are free to implement the Cloneable interface.
 *
 * @author Benjamin Renaud
 * @since 1.2
 *
 *
 * @see MessageDigest
 */

public abstract class MessageDigestSpi {

    // for re-use in engineUpdate(ByteBuffer input)
    private byte[] tempArray;

    
Returns the digest length in bytes.

This concrete method has been added to this previously-defined
abstract class. (For backwards compatibility, it cannot be abstract.)

The default behavior is to return 0.

This method may be overridden by a provider to return the digest
length.

Returns:the digest length in bytes.
Since:1.2
/**
     * Returns the digest length in bytes.
     *
     * <p>This concrete method has been added to this previously-defined
     * abstract class. (For backwards compatibility, it cannot be abstract.)
     *
     * <p>The default behavior is to return 0.
     *
     * <p>This method may be overridden by a provider to return the digest
     * length.
     *
     * @return the digest length in bytes.
     *
     * @since 1.2
     */
    protected int engineGetDigestLength() {
        return 0;
    }

    
Updates the digest using the specified byte.

Params:
  • input – the byte to use for the update.
/**
     * Updates the digest using the specified byte.
     *
     * @param input the byte to use for the update.
     */
    protected abstract void engineUpdate(byte input);

    
Updates the digest using the specified array of bytes,
starting at the specified offset.

Params:
  • input – the array of bytes to use for the update.
  • offset – the offset to start from in the array of bytes.
  • len – the number of bytes to use, starting at offset.
/**
     * Updates the digest using the specified array of bytes,
     * starting at the specified offset.
     *
     * @param input the array of bytes to use for the update.
     *
     * @param offset the offset to start from in the array of bytes.
     *
     * @param len the number of bytes to use, starting at
     * {@code offset}.
     */
    protected abstract void engineUpdate(byte[] input, int offset, int len);

    
Update the digest using the specified ByteBuffer. The digest is updated using the input.remaining() bytes starting at input.position(). Upon return, the buffer's position will be equal to its limit; its limit will not have changed. 
Params:
  • input – the ByteBuffer
Since:1.5
/**
     * Update the digest using the specified ByteBuffer. The digest is
     * updated using the {@code input.remaining()} bytes starting
     * at {@code input.position()}.
     * Upon return, the buffer's position will be equal to its limit;
     * its limit will not have changed.
     *
     * @param input the ByteBuffer
     * @since 1.5
     */
    protected void engineUpdate(ByteBuffer input) {
        if (input.hasRemaining() == false) {
            return;
        }
        if (input.hasArray()) {
            byte[] b = input.array();
            int ofs = input.arrayOffset();
            int pos = input.position();
            int lim = input.limit();
            engineUpdate(b, ofs + pos, lim - pos);
            input.position(lim);
        } else {
            int len = input.remaining();
            int n = JCAUtil.getTempArraySize(len);
            if ((tempArray == null) || (n > tempArray.length)) {
                tempArray = new byte[n];
            }
            while (len > 0) {
                int chunk = Math.min(len, tempArray.length);
                input.get(tempArray, 0, chunk);
                engineUpdate(tempArray, 0, chunk);
                len -= chunk;
            }
        }
    }

    
Completes the hash computation by performing final operations such as padding. Once engineDigest has been called, the engine should be reset (see engineReset). Resetting is the responsibility of the engine implementor. 
Returns:the array of bytes for the resulting hash value.
/**
     * Completes the hash computation by performing final
     * operations such as padding. Once {@code engineDigest} has
     * been called, the engine should be reset (see
     * {@link #engineReset() engineReset}).
     * Resetting is the responsibility of the
     * engine implementor.
     *
     * @return the array of bytes for the resulting hash value.
     */
    protected abstract byte[] engineDigest();

    
Completes the hash computation by performing final operations such as padding. Once engineDigest has been called, the engine should be reset (see engineReset). Resetting is the responsibility of the engine implementor. This method should be abstract, but we leave it concrete for binary compatibility. Knowledgeable providers should override this method. 
Params:
  • buf – the output buffer in which to store the digest
  • offset – offset to start from in the output buffer
  • len – number of bytes within buf allotted for the digest.
Both this default implementation and the SUN provider do not
return partial digests.  The presence of this parameter is solely
for consistency in our API's.  If the value of this parameter is less
than the actual digest length, the method will throw a DigestException.
This parameter is ignored if its value is greater than or equal to
the actual digest length.
Throws:
Returns:the length of the digest stored in the output buffer.
Since:1.2
/**
     * Completes the hash computation by performing final
     * operations such as padding. Once {@code engineDigest} has
     * been called, the engine should be reset (see
     * {@link #engineReset() engineReset}).
     * Resetting is the responsibility of the
     * engine implementor.
     *
     * This method should be abstract, but we leave it concrete for
     * binary compatibility.  Knowledgeable providers should override this
     * method.
     *
     * @param buf the output buffer in which to store the digest
     *
     * @param offset offset to start from in the output buffer
     *
     * @param len number of bytes within buf allotted for the digest.
     * Both this default implementation and the SUN provider do not
     * return partial digests.  The presence of this parameter is solely
     * for consistency in our API's.  If the value of this parameter is less
     * than the actual digest length, the method will throw a DigestException.
     * This parameter is ignored if its value is greater than or equal to
     * the actual digest length.
     *
     * @return the length of the digest stored in the output buffer.
     *
     * @exception DigestException if an error occurs.
     *
     * @since 1.2
     */
    protected int engineDigest(byte[] buf, int offset, int len)
                                                throws DigestException {

        byte[] digest = engineDigest();
        if (len < digest.length)
                throw new DigestException("partial digests not returned");
        if (buf.length - offset < digest.length)
                throw new DigestException("insufficient space in the output "
                                          + "buffer to store the digest");
        System.arraycopy(digest, 0, buf, offset, digest.length);
        return digest.length;
    }

    
Resets the digest for further use.

/**
     * Resets the digest for further use.
     */
    protected abstract void engineReset();

    
Returns a clone if the implementation is cloneable.

Throws:
Returns:a clone if the implementation is cloneable.
/**
     * 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 {@code Cloneable}.
     */
    public Object clone() throws CloneNotSupportedException {
        if (this instanceof Cloneable) {
            return super.clone();
        } else {
            throw new CloneNotSupportedException();
        }
    }
}