MessageDigest

public abstract class MessageDigest extends MessageDigestSpi

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:

 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+
These algorithms are described in the MessageDigest section of the Java Cryptography Architecture Standard Algorithm Name Documentation.

Protected Constructor Summary

MessageDigest(String algorithm)
Creates a message digest with the specified algorithm name.

Public Method Summary

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 Method Summary