- java.lang.Object
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- java.security.MessageDigestSpi
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- java.security.MessageDigest
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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 pointreset
can be called to reset the digest. Once all the data to be updated has been updated, one of thedigest
methods should be called to complete the hash computation.The
digest
method can be called once for a given number of updates. Afterdigest
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-256"); 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 thisMessageDigest
class; all the methods in the superclass are intended for cryptographic service providers who wish to supply their own implementations of message digest algorithms.Every implementation of the Java platform is required to support the following standard
MessageDigest
algorithms:- MD5
- SHA-1
- SHA-256
- See Also:
DigestInputStream
,DigestOutputStream
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Constructor Summary
Constructors Modifier Constructor and Description protected
MessageDigest(String algorithm)
Creates a message digest with the specified algorithm name.
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Method Summary
Methods Modifier and Type Method and Description 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
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Constructor Detail
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MessageDigest
protected MessageDigest(String algorithm)
Creates a message digest with the specified algorithm name.- Parameters:
algorithm
- 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.
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Method Detail
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getInstance
public static MessageDigest getInstance(String algorithm) throws NoSuchAlgorithmException
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
- 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:
- a Message Digest object that implements the specified algorithm.
- Throws:
NoSuchAlgorithmException
- if no Provider supports a MessageDigestSpi implementation for the specified algorithm.- See Also:
Provider
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getInstance
public static MessageDigest getInstance(String algorithm, String provider) throws NoSuchAlgorithmException, NoSuchProviderException
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
- 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
- the name of the provider.- Returns:
- 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:
Provider
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getInstance
public static MessageDigest getInstance(String algorithm, Provider provider) throws NoSuchAlgorithmException
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 the MessageDigest section in the Java Cryptography Architecture Standard Algorithm Name Documentation for information about standard algorithm names.provider
- the provider.- Returns:
- 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.- Since:
- 1.4
- See Also:
Provider
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getProvider
public final Provider getProvider()
Returns the provider of this message digest object.- Returns:
- the provider of this message digest object
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update
public void update(byte input)
Updates the digest using the specified byte.- Parameters:
input
- the byte with which to update the digest.
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update
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.offset
- the offset to start from in the array of bytes.len
- the number of bytes to use, starting atoffset
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update
public void update(byte[] input)
Updates the digest using the specified array of bytes.- Parameters:
input
- the array of bytes.
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update
public final void update(ByteBuffer input)
Update the digest using the specified ByteBuffer. The digest is updated using theinput.remaining()
bytes starting atinput.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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digest
public byte[] digest()
Completes the hash computation by performing final operations such as padding. The digest is reset after this call is made.- Returns:
- the array of bytes for the resulting hash value.
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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.- Parameters:
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- Returns:
- the number of bytes placed into
buf
- Throws:
DigestException
- if an error occurs.
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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 callsupdate(input)
, passing the input array to theupdate
method, then callsdigest()
.- Parameters:
input
- the input to be updated before the digest is completed.- Returns:
- the array of bytes for the resulting hash value.
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toString
public String toString()
Returns a string representation of this message digest object.
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isEqual
public static boolean isEqual(byte[] digesta, byte[] digestb)
Compares two digests for equality. Does a simple byte compare.- Parameters:
digesta
- one of the digests to compare.digestb
- the other digest to compare.- Returns:
- true if the digests are equal, false otherwise.
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reset
public void reset()
Resets the digest for further use.
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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-256"). See the MessageDigest section in the Java Cryptography Architecture Standard Algorithm Name Documentation for information about standard algorithm names.- Returns:
- the name of the algorithm
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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.- Returns:
- the digest length in bytes, or 0 if this operation is not supported by the provider and the implementation is not cloneable.
- Since:
- 1.2
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clone
public Object clone() throws CloneNotSupportedException
Returns a clone if the implementation is cloneable.- Overrides:
clone
in classMessageDigestSpi
- Returns:
- a clone if the implementation is cloneable.
- Throws:
CloneNotSupportedException
- if this is called on an implementation that does not supportCloneable
.- See Also:
Cloneable
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