public
abstract
class
MessageDigest
extends MessageDigestSpi
| java.lang.Object | ||
| ↳ | java.security.MessageDigestSpi | |
| ↳ | java.security.MessageDigest | |
This MessageDigest class provides applications the functionality of a message digest algorithm, such as SHA-1 or SHA-256. 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:
Developers
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.
Android provides the following MessageDigest algorithms:
| Name | Supported (API Levels) |
|---|---|
| MD5 | 1+ |
| SHA-1 | 1+ |
| SHA-224 | 1–8,22+ |
| SHA-256 | 1+ |
| SHA-384 | 1+ |
| SHA-512 | 1+ |
See also:
Protected constructors | |
|---|---|
MessageDigest(String algorithm)
Creates a message digest with the specified algorithm name. |
|
Public methods | |
|---|---|
Object
|
clone()
Returns a clone if the implementation is cloneable. |
int
|
digest(byte[] buf, int offset, int len)
Completes the hash computation by performing final operations such as padding. |
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. |
final
String
|
getAlgorithm()
Returns a string that identifies the algorithm, independent of implementation details. |
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. |
static
MessageDigest
|
getInstance(String algorithm)
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. |
static
MessageDigest
|
getInstance(String algorithm, Provider provider)
Returns a MessageDigest object that implements the specified digest algorithm. |
final
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 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. |
final
void
|
update(ByteBuffer input)
Update the digest using the specified ByteBuffer. |
void
|
update(byte input)
Updates the digest using the specified byte. |
Inherited methods | |
|---|---|
 From
class
java.security.MessageDigestSpi
| |
From
class
java.lang.Object
| |
MessageDigest (String algorithm)
Creates a message digest with the specified algorithm name.
| Parameters | |
|---|---|
algorithm |
String:
the standard name of the digest algorithm.
See the MessageDigest section in the
Java Cryptography Architecture Standard Algorithm Name Documentation
for information about standard algorithm names.
|
Object clone ()
Returns a clone if the implementation is cloneable.
| Returns | |
|---|---|
Object |
a clone if the implementation is cloneable. |
| Throws | |
|---|---|
CloneNotSupportedException |
if this is called on an
implementation that does not support Cloneable.
|
int digest (byte[] buf,
int offset,
int len)
Completes the hash computation by performing final operations such as padding. The digest is reset after this call is made.
| Parameters | |
|---|---|
buf |
byte:
output buffer for the computed digest |
offset |
int:
offset into the output buffer to begin storing the digest |
len |
int:
number of bytes within buf allotted for the digest |
| Returns | |
|---|---|
int |
the number of bytes placed into buf |
| Throws | |
|---|---|
DigestException |
if an error occurs. |
byte[] digest ()
Completes the hash computation by performing final operations such as padding. The digest is reset after this call is made.
| Returns | |
|---|---|
byte[] |
the array of bytes for the resulting hash value. |
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().
| Parameters | |
|---|---|
input |
byte:
the input to be updated before the digest is
completed. |
| Returns | |
|---|---|
byte[] |
the array of bytes for the resulting hash value. |
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 the MessageDigest section in the Java Cryptography Architecture Standard Algorithm Name Documentation for information about standard algorithm names.
| Returns | |
|---|---|
String |
the name of the algorithm |
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.
| Returns | |
|---|---|
int |
the digest length in bytes, or 0 if this operation is not supported by the provider and the implementation is not cloneable. |
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() method.
| Parameters | |
|---|---|
algorithm |
String:
the name of the algorithm requested.
See the MessageDigest section in the
Java Cryptography Architecture Standard Algorithm Name Documentation
for information about standard algorithm names. |
| Returns | |
|---|---|
MessageDigest |
a Message Digest object that implements the specified algorithm. |
| Throws | |
|---|---|
NoSuchAlgorithmException |
if no Provider supports a MessageDigestSpi implementation for the specified algorithm. |
See also:
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. 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.
| Parameters | |
|---|---|
algorithm |
String:
the name of the algorithm requested.
See the MessageDigest section in the
Java Cryptography Architecture Standard Algorithm Name Documentation
for information about standard algorithm names. |
provider |
String:
the name of the provider. |
| Returns | |
|---|---|
MessageDigest |
a MessageDigest object that implements the specified algorithm. |
| Throws | |
|---|---|
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. |
See also:
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. Note that the specified Provider object does not have to be registered in the provider list.
| Parameters | |
|---|---|
algorithm |
String:
the name of the algorithm requested.
See the MessageDigest section in the
Java Cryptography Architecture Standard Algorithm Name Documentation
for information about standard algorithm names. |
provider |
Provider:
the provider. |
| Returns | |
|---|---|
MessageDigest |
a MessageDigest object that implements the specified algorithm. |
| Throws | |
|---|---|
NoSuchAlgorithmException |
if a MessageDigestSpi implementation for the specified algorithm is not available from the specified Provider object. |
IllegalArgumentException |
if the specified provider is null. |
See also:
Provider getProvider ()
Returns the provider of this message digest object.
| Returns | |
|---|---|
Provider |
the provider of this message digest object |
boolean isEqual (byte[] digesta,
byte[] digestb)
Compares two digests for equality. Does a simple byte compare.
| Parameters | |
|---|---|
digesta |
byte:
one of the digests to compare. |
digestb |
byte:
the other digest to compare. |
| Returns | |
|---|---|
boolean |
true if the digests are equal, false otherwise. |
String toString ()
Returns a string representation of this message digest object.
| Returns | |
|---|---|
String |
a string representation of the object. |
void update (byte[] input)
Updates the digest using the specified array of bytes.
| Parameters | |
|---|---|
input |
byte:
the 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.
| Parameters | |
|---|---|
input |
byte:
the array of bytes. |
offset |
int:
the offset to start from in the array of bytes. |
len |
int:
the number of bytes to use, starting at
offset.
|
void update (ByteBuffer input)
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 |
ByteBuffer:
the ByteBuffer |
void update (byte input)
Updates the digest using the specified byte.
| Parameters | |
|---|---|
input |
byte:
the byte with which to update the digest.
|