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| java.lang.Object
 java.security.MessageDigestSpi
java.security.MessageDigest
| MessageDigest | | abstract public class MessageDigest extends MessageDigestSpi (Code) | | 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
MessageDigest.update(byte) update methods. At any point
MessageDigest.reset() reset can be called
to reset the digest. Once all the data to be updated has been
updated, one of the
MessageDigest.digest() 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.
author:
Benjamin Renaud
version:
1.87, 05/05/07
See Also: DigestInputStream
See Also: DigestOutputStream |
| Constructor Summary | |
| protected | MessageDigest(String algorithm)
Creates a message digest with the specified algorithm name.
Parameters:
algorithm - the standard name of the digest algorithm. |
| Method Summary | |
| public Object | clone()
Returns a clone if the implementation is cloneable. | | public byte[] | digest()
Completes the hash computation by performing final operations
such as padding. | | public int | digest(byte[] buf, int offset, int len)
Completes the hash computation by performing final operations
such as padding. | | public byte[] | digest(byte[] input)
Performs a final update on the digest using the specified array
of bytes, then completes the digest computation. | | final public String | getAlgorithm()
Returns a string that identifies the algorithm, independent of
implementation details. | | final public 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. | | public static MessageDigest | getInstance(String algorithm)
Returns a MessageDigest object that implements the specified digest
algorithm.
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 Security.getProviders() method.
Parameters:
algorithm - the name of the algorithm requested. | | public static MessageDigest | getInstance(String algorithm, String provider)
Returns a MessageDigest object that implements the specified digest
algorithm.
A new MessageDigest object encapsulating the
MessageDigestSpi implementation from the specified provider
is returned. | | public static MessageDigest | getInstance(String algorithm, Provider provider)
Returns a MessageDigest object that implements the specified digest
algorithm.
A new MessageDigest object encapsulating the
MessageDigestSpi implementation from the specified Provider
object is returned. | | final public Provider | getProvider()
Returns the provider of this message digest object. | | public static boolean | isEqual(byte digesta, byte digestb)
Compares two digests for equality. | | public void | reset()
Resets the digest for further use. | | public String | toString()
Returns a string representation of this message digest object. | | public void | update(byte input)
Updates the digest using the specified byte. | | public void | update(byte[] input, int offset, int len)
Updates the digest using the specified array of bytes, starting
at the specified offset.
Parameters:
input - the array of bytes.
Parameters:
offset - the offset to start from in the array of bytes.
Parameters:
len - the number of bytes to use, starting at offset. | | public void | update(byte[] input)
Updates the digest using the specified array of bytes. | | final public void | update(ByteBuffer input)
Update the digest using the specified ByteBuffer. |
| digest | | public byte[] digest()(Code) | | 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 int digest(byte[] buf, int offset, int len) throws DigestException(Code) | | Completes the hash computation by performing final operations
such as padding. The digest is reset after this call is made.
Parameters:
buf - output buffer for the computed digest
Parameters:
offset - offset into the output buffer to begin storing the digest
Parameters:
len - number of bytes within buf allotted for the digest the number of bytes placed into buf
exception:
DigestException - if an error occurs. |
| digest | | public byte[] digest(byte[] input)(Code) | | Performs a final update on the digest using the specified array
of bytes, then completes the digest computation. That is, this
method first calls
MessageDigest.update(byte[]) update(input) ,
passing the input array to the update method,
then calls
MessageDigest.digest() digest() .
Parameters:
input - the input to be updated before the digest iscompleted. the array of bytes for the resulting hash value. |
| getAlgorithm | | final public String getAlgorithm()(Code) | | 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 | | final public int getDigestLength()(Code) | | 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 notsupported by the provider and the implementation is not cloneable.
since:
1.2 |
| getInstance | | public static MessageDigest getInstance(String algorithm) throws NoSuchAlgorithmException(Code) | | Returns a MessageDigest object that implements the specified digest
algorithm.
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 Security.getProviders() method.
Parameters:
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 that implements the specified algorithm.
exception:
NoSuchAlgorithmException - if no Provider supports aMessageDigestSpi implementation for thespecified algorithm.
See Also: Provider |
| getInstance | | public static MessageDigest getInstance(String algorithm, String provider) throws NoSuchAlgorithmException, NoSuchProviderException(Code) | | Returns a MessageDigest object that implements the specified digest
algorithm.
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 Security.getProviders() method.
Parameters:
algorithm - the name of the algorithm requested. See Appendix A in the Java Cryptography Architecture API Specification & Reference for information about standard algorithm names.
Parameters:
provider - the name of the provider. a MessageDigest object that implements the specified algorithm.
exception:
NoSuchAlgorithmException - if a MessageDigestSpiimplementation for the specified algorithm is notavailable from the specified provider.
exception:
NoSuchProviderException - if the specified provider is notregistered in the security provider list.
exception:
IllegalArgumentException - if the provider name is nullor empty.
See Also: Provider
See Also: |
| getInstance | | public static MessageDigest getInstance(String algorithm, Provider provider) throws NoSuchAlgorithmException(Code) | | Returns a MessageDigest object that implements the specified digest
algorithm.
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.
Parameters:
algorithm - the name of the algorithm requested. See Appendix A in the Java Cryptography Architecture API Specification & Reference for information about standard algorithm names.
Parameters:
provider - the provider. a MessageDigest object that implements the specified algorithm.
exception:
NoSuchAlgorithmException - if a MessageDigestSpiimplementation for the specified algorithm is not availablefrom the specified Provider object.
exception:
IllegalArgumentException - if the specified provider is null.
See Also: Provider
since:
1.4 |
| getProvider | | final public Provider getProvider()(Code) | | Returns the provider of this message digest object.
the provider of this message digest object |
| isEqual | | public static boolean isEqual(byte digesta, byte digestb)(Code) | | Compares two digests for equality. Does a simple byte compare.
Parameters:
digesta - one of the digests to compare.
Parameters:
digestb - the other digest to compare. true if the digests are equal, false otherwise. |
| reset | | public void reset()(Code) | | Resets the digest for further use.
|
| toString | | public String toString()(Code) | | Returns a string representation of this message digest object.
|
| update | | public void update(byte input)(Code) | | Updates the digest using the specified byte.
Parameters:
input - the byte with which to update the digest. |
| update | | public void update(byte[] input, int offset, int len)(Code) | | Updates the digest using the specified array of bytes, starting
at the specified offset.
Parameters:
input - the array of bytes.
Parameters:
offset - the offset to start from in the array of bytes.
Parameters:
len - the number of bytes to use, starting at offset. |
| update | | public void update(byte[] input)(Code) | | Updates the digest using the specified array of bytes.
Parameters:
input - the array of bytes. |
| update | | final public void update(ByteBuffer input)(Code) | | 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.
Parameters:
input - the ByteBuffer
since:
1.5 |
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