public abstract class MessageDigest extends MessageDigestSpi
A MessageDigest object starts out initialized. The data is
processed through it using the update
methods. At any point reset can be called
to reset the digest. Once all the data to be updated has been
updated, one of the digest methods should
be called to complete the hash computation.
The digest method can be called once for a given number
of updates. After digest has been called, the MessageDigest
object is reset to its initialized state.
Implementations are free to implement the Cloneable interface. Client applications can test cloneability by attempting cloning and catching the CloneNotSupportedException:
MessageDigest md = MessageDigest.getInstance("SHA");
try {
md.update(toChapter1);
MessageDigest tc1 = md.clone();
byte[] toChapter1Digest = tc1.digest();
md.update(toChapter2);
...etc.
} catch (CloneNotSupportedException cnse) {
throw new DigestException("couldn't make digest of partial content");
}
Note that if a given implementation is not cloneable, it is still possible to compute intermediate digests by instantiating several instances, if the number of digests is known in advance.
Note that this class is abstract and extends from
MessageDigestSpi for historical reasons.
Application developers should only take notice of the methods defined in
this MessageDigest class; all the methods in
the superclass are intended for cryptographic service providers who wish to
supply their own implementations of message digest algorithms.
DigestInputStream,
DigestOutputStream| Modifier | Constructor and Description |
|---|---|
protected |
MessageDigest(String algorithm)
Creates a message digest with the specified algorithm name.
|
| Modifier and Type | Method and Description |
|---|---|
Object |
clone()
Returns a clone if the implementation is cloneable.
|
byte[] |
digest()
Completes the hash computation by performing final operations
such as padding.
|
byte[] |
digest(byte[] input)
Performs a final update on the digest using the specified array
of bytes, then completes the digest computation.
|
int |
digest(byte[] buf,
int offset,
int len)
Completes the hash computation by performing final operations
such as padding.
|
String |
getAlgorithm()
Returns a string that identifies the algorithm, independent of
implementation details.
|
int |
getDigestLength()
Returns the length of the digest in bytes, or 0 if this operation is
not supported by the provider and the implementation is not cloneable.
|
static MessageDigest |
getInstance(String algorithm)
Generates a MessageDigest object that implements the specified digest
algorithm.
|
static MessageDigest |
getInstance(String algorithm,
Provider provider)
Generates a MessageDigest object implementing the specified
algorithm, as supplied from the specified provider, if such an
algorithm is available from the provider.
|
static MessageDigest |
getInstance(String algorithm,
String provider)
Generates a MessageDigest object implementing the specified
algorithm, as supplied from the specified provider, if such an
algorithm is available from the provider.
|
Provider |
getProvider()
Returns the provider of this message digest object.
|
static boolean |
isEqual(byte[] digesta,
byte[] digestb)
Compares two digests for equality.
|
void |
reset()
Resets the digest for further use.
|
String |
toString()
Returns a string representation of this message digest object.
|
void |
update(byte input)
Updates the digest using the specified byte.
|
void |
update(byte[] input)
Updates the digest using the specified array of bytes.
|
void |
update(byte[] input,
int offset,
int len)
Updates the digest using the specified array of bytes, starting
at the specified offset.
|
engineDigest, engineDigest, engineGetDigestLength, engineReset, engineUpdate, engineUpdateprotected MessageDigest(String algorithm)
algorithm - the standard name of the digest algorithm.
See Appendix A in the
Java Cryptography Architecture API Specification & Reference
for information about standard algorithm names.public static MessageDigest getInstance(String algorithm) throws NoSuchAlgorithmException
algorithm - the name of the algorithm requested.
See Appendix A in the
Java Cryptography Architecture API Specification & Reference
for information about standard algorithm names.NoSuchAlgorithmException - if the algorithm is
not available in the caller's environment.public static MessageDigest getInstance(String algorithm, String provider) throws NoSuchAlgorithmException, NoSuchProviderException
algorithm - the name of the algorithm requested.
See Appendix A in the
Java Cryptography Architecture API Specification & Reference
for information about standard algorithm names.provider - the name of the provider.NoSuchAlgorithmException - if the algorithm is
not available in the package supplied by the requested
provider.NoSuchProviderException - if the provider is not
available in the environment.IllegalArgumentException - if the provider name is null
or empty.Providerpublic static MessageDigest getInstance(String algorithm, Provider provider) throws NoSuchAlgorithmException
provider doesn't have to be registered.algorithm - the name of the algorithm requested.
See Appendix A in the
Java Cryptography Architecture API Specification & Reference
for information about standard algorithm names.provider - the provider.NoSuchAlgorithmException - if the algorithm is
not available in the package supplied by the requested
provider.IllegalArgumentException - if the provider is
null.Providerpublic final Provider getProvider()
public void update(byte input)
input - the byte with which to update the digest.public void update(byte[] input,
int offset,
int len)
input - the array of bytes.offset - the offset to start from in the array of bytes.len - the number of bytes to use, starting at
offset.public void update(byte[] input)
input - the array of bytes.public byte[] digest()
public int digest(byte[] buf,
int offset,
int len)
throws DigestException
buf - output buffer for the computed digestoffset - offset into the output buffer to begin storing the digestlen - number of bytes within buf allotted for the digestbufDigestException - if an error occurs.public byte[] digest(byte[] input)
update(input),
passing the input array to the update method,
then calls digest().input - the input to be updated before the digest is
completed.public String toString()
public static boolean isEqual(byte[] digesta,
byte[] digestb)
digesta - one of the digests to compare.digestb - the other digest to compare.public void reset()
public final String getAlgorithm()
public final int getDigestLength()
public Object clone() throws CloneNotSupportedException
clone in class MessageDigestSpiCloneNotSupportedException - if this is called on an
implementation that does not support Cloneable.CloneableCopyright © 2012 CableLabs. All Rights Reserved.