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MessageDigestSpi.javaAPI DocAndroid 1.5 API5686Wed May 06 22:41:06 BST 2009java.security

MessageDigestSpi

public abstract class MessageDigestSpi extends Object
{@code MessageDigestSpi} is the Service Provider Interface (SPI) definition for {@link MessageDigest}. Examples of digest algorithms are MD5 and SHA. A digest is a secure one way hash function for a stream of bytes. It acts like a fingerprint for a stream of bytes.
see
MessageDigest
since
Android 1.0

Fields Summary
Constructors Summary
Methods Summary
public java.lang.Objectclone()

        return super.clone();
protected abstract byte[]engineDigest()
Computes and returns the final hash value for this {@link MessageDigestSpi}. After the digest is computed the receiver is reset.

return
the computed one way hash value.
see
#engineReset()
since
Android 1.0

protected intengineDigest(byte[] buf, int offset, int len)
Computes and stores the final hash value for this
{@link MessageDigestSpi}. After the digest is computed the receiver is
reset.
param
buf
the buffer to store the result in.
param
offset
the index of the first byte in {@code buf} to store in.
param
len
the number of bytes allocated for the digest.
return
the number of bytes written to {@code buf}.
throws
DigestException
if an error occures.
throws
IllegalArgumentException
if {@code offset} or {@code len} are not valid in respect to
{@code buf}.
see
#engineReset()
since
Android 1.0
        if (len < engineGetDigestLength()) {
            engineReset();
            throw new DigestException(Messages.getString("security.1B"));  //$NON-NLS-1$
        }
        if (offset < 0) {
            engineReset();
            throw new DigestException(Messages.getString("security.1C")); //$NON-NLS-1$
        }
        if (offset + len > buf.length) {
            engineReset();
            throw new DigestException(Messages.getString("security.1D")); //$NON-NLS-1$
        }
        byte tmp[] = engineDigest();
        if (len < tmp.length) {
            throw new DigestException(Messages.getString("security.1B")); //$NON-NLS-1$
        }
        System.arraycopy(tmp, 0, buf, offset, tmp.length);
        return tmp.length;            
    
protected intengineGetDigestLength()
Returns the engine digest length in bytes. If the implementation does not
implement this function {@code 0} is returned.
return
the digest length in bytes, or {@code 0}.
since
Android 1.0
        return 0;
    
protected abstract voidengineReset()
Puts this {@code MessageDigestSpi} back in an initial state, such that it
is ready to compute a one way hash value.
since
Android 1.0
protected abstract voidengineUpdate(byte input)
Updates this {@code MessageDigestSpi} using the given {@code byte}.
param
input
the {@code byte} to update this {@code MessageDigestSpi} with.
see
#engineReset()
since
Android 1.0
protected abstract voidengineUpdate(byte[] input, int offset, int len)
Updates this {@code MessageDigestSpi} using the given {@code byte[]}.
param
input
the {@code byte} array.
param
offset
the index of the first byte in {@code input} to update from.
param
len
the number of bytes in {@code input} to update from.
throws
IllegalArgumentException
if {@code offset} or {@code len} are not valid in respect to
{@code input}.
since
Android 1.0
protected voidengineUpdate(java.nio.ByteBuffer input)
Updates this {@code MessageDigestSpi} using the given {@code input}.
param
input
the {@code ByteBuffer}.
since
Android 1.0
        if (!input.hasRemaining()) {
            return;
        }
        byte[] tmp;
        if (input.hasArray()) {
            tmp = input.array();
            int offset = input.arrayOffset();
            int position = input.position();
            int limit = input.limit();
            engineUpdate(tmp, offset+position, limit - position);
            input.position(limit);
        } else {
            tmp = new byte[input.limit() - input.position()];
            input.get(tmp);
            engineUpdate(tmp, 0, tmp.length);
        }