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Java™ Platform Standard Ed. 6 |
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java.lang.Object java.security.MessageDigestSpi java.security.MessageDigest
public abstract 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); ...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
Constructor Summary | |
---|---|
protected |
MessageDigest(String algorithm)
Creates a message digest with the specified algorithm name. |
Method Summary | |
---|---|
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)
Returns a MessageDigest object that implements the specified digest algorithm. |
static MessageDigest |
getInstance(String algorithm,
Provider provider)
Returns a MessageDigest object that implements the specified digest algorithm. |
static MessageDigest |
getInstance(String algorithm,
String provider)
Returns a MessageDigest object that implements the specified digest algorithm. |
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. |
void |
update(ByteBuffer input)
Update the digest using the specified ByteBuffer. |
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 Detail |
---|
protected 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.Method Detail |
---|
public static MessageDigest getInstance(String algorithm) throws NoSuchAlgorithmException
This method traverses the list of registered security Providers, starting with the most preferred Provider. A new MessageDigest object encapsulating the MessageDigestSpi implementation from the first Provider that supports the specified algorithm is returned.
Note that the list of registered providers may be retrieved via
the Security.getProviders()
method.
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 no Provider supports a
MessageDigestSpi implementation for the
specified algorithm.Provider
public static MessageDigest getInstance(String algorithm, String provider) throws NoSuchAlgorithmException, NoSuchProviderException
A new MessageDigest object encapsulating the MessageDigestSpi implementation from the specified provider is returned. The specified provider must be registered in the security provider list.
Note that the list of registered providers may be retrieved via
the Security.getProviders()
method.
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 a MessageDigestSpi
implementation for the specified algorithm is not
available from the specified provider.
NoSuchProviderException
- if the specified provider is not
registered in the security provider list.
IllegalArgumentException
- if the provider name is null
or empty.Provider
public static MessageDigest getInstance(String algorithm, Provider provider) throws NoSuchAlgorithmException
A new MessageDigest object encapsulating the MessageDigestSpi implementation from the specified Provider object is returned. Note that the specified Provider object does not have to be registered in the provider list.
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 a MessageDigestSpi
implementation for the specified algorithm is not available
from the specified Provider object.
IllegalArgumentException
- if the specified provider is null.Provider
public 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 final void update(ByteBuffer input)
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.
input
- the ByteBufferpublic 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 digest
buf
DigestException
- 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()
toString
in class Object
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 MessageDigestSpi
CloneNotSupportedException
- if this is called on an
implementation that does not support Cloneable
.Cloneable
|
Java™ Platform Standard Ed. 6 |
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