java.security
Class MessageDigest
This
MessageDigest
class provides applications 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.
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);
// ...
}
catch (CloneNotSupportedException x)
{
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.
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, 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.
|
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.
|
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.
|
clone , equals , finalize , getClass , hashCode , notify , notifyAll , toString , wait , wait , wait |
MessageDigest
protected MessageDigest(String algorithm)
Creates a message digest with the specified algorithm name.
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.
digest
public byte[] digest()
Completes the hash computation by performing final operations such as
padding. The digest is reset after this call is made.
- the array of bytes for the resulting hash value.
digest
public byte[] digest(byte[] input)
Performs a final update on the digest using the specified array of bytes,
then completes the digest computation. That is, this method first calls
update(input)
, passing the input array to the update()
method, then calls digest()
.
input
- the input to be updated before the digest is completed.
- the array of bytes for the resulting hash value.
digest
public int digest(byte[] buf,
int offset,
int len)
throws DigestException
Completes the hash computation by performing final operations such as
padding. The digest is reset after this call is made.
buf
- An output buffer for the computed digest.offset
- The offset into the output buffer to begin storing the digest.len
- The number of bytes within buf allotted for the digest.
- The number of bytes placed into buf.
getAlgorithm
public final String getAlgorithm()
Returns a string that identifies the algorithm, independent of
implementation details. The name should be a standard Java Security name
(such as "SHA"
, "MD5"
, and so on). See Appendix
A in the Java Cryptography Architecture API Specification & Reference
for information about standard algorithm names.
- the name of the algorithm.
getDigestLength
public final 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.
- the digest length in bytes, or
0
if this operation is
not supported by the provider and the implementation is not cloneable.
getInstance
public static MessageDigest getInstance(String algorithm)
throws NoSuchAlgorithmException
Generates a MessageDigest
object that implements the specified
digest algorithm. If the default provider package provides an
implementation of the requested digest algorithm, an instance of
MessageDigest
containing that implementation is returned. If
the algorithm is not available in the default package, other packages are
searched.
algorithm
- the name of the algorithm requested. See Appendix A in the
Java Cryptography Architecture API Specification & Reference for
information about standard algorithm names.
- a Message Digest object implementing the specified algorithm.
getInstance
public static MessageDigest getInstance(String algorithm,
String provider)
throws NoSuchAlgorithmException,
NoSuchProviderException
Generates a MessageDigest
object implementing the specified
algorithm, as supplied from the specified provider, if such an algorithm is
available from the provider.
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.
- a Message Digest object implementing the specified algorithm.
getInstance
public static MessageDigest getInstance(String algorithm,
Provider provider)
throws NoSuchAlgorithmException
Generates a MessageDigest
object implementing the specified
algorithm, as supplied from the specified provider, if such an algorithm
is available from the provider. Note: the 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.
- a Message Digest object implementing the specified algorithm.
getProvider
public final Provider getProvider()
Returns the provider of this message digest object.
- the provider of this message digest object.
isEqual
public static boolean isEqual(byte[] digesta,
byte[] digestb)
Compares two digests for equality. Does a simple byte compare.
digesta
- one of the digests to compare.digestb
- the other digest to compare.
true
if the digests are equal, false
otherwise.
reset
public void reset()
Resets the digest for further use.
toString
public String toString()
Returns a string representation of this message digest object.
- toString in interface Object
- a string representation of the object.
update
public void update(byte input)
Updates the digest using the specified byte.
input
- the byte with which to update the digest.
update
public void update(byte[] input)
Updates the digest using the specified array of bytes.
input
- the array of bytes.
update
public void update(byte[] input,
int offset,
int len)
Updates the digest using the specified array of bytes, starting at the
specified offset.
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.
MessageDigest.java --- The message digest interface.
Copyright (C) 1999, 2002, 2003, 2006 Free Software Foundation, Inc.
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