Use messagedigest to complete MD5 Encryption

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• Java. Security. messagedigest

Java encryption technology: Message Digest.

A message digest is a digital fingerprint of a data block. Calculate a data block of any length and generate a unique fingerprint (for sha1, a 20-byte binary array ).

The message digest has two basic attributes:

It is difficult for two different packets to generate the same abstract.
It is difficult to generate a message for a specified digest, and the specified digest is calculated by the corresponding digest.
Representatives: sha1 of the National Institute of Standards and Technology and MD5 proposed by Ronald Rivest of the Massachusetts Institute of Technology

 

Java. Security. messagedigest

java.lang.Object   |   +----java.security.MessageDigest

Public abstract class Messagedigest

Extends object

Messagedigest provides message digest algorithms, such as MD5 or Sha. A message digest is a secure one-way hash function that uses data of any size and outputs a fixed-length hash value.

Like other algorithm-based classes in Java security, messagedigest has two main components:

Message Digest API(Application Interface)

This is the interface of the method called by the application of the message digest service. This API is composed of all public methods.

Message Digest SPI(Service Provider Interface)

This interface is implemented by the provider that provides special algorithms. It is prefixed by all names Engine. Each such method is called by a public API method with the corresponding name. For example, engineResetMethod resetMethod call. The SPI method is abstract; the provider must provide a specific implementation.

The messagedigest object is initialized at startup. Use the update method to process data. The reset summary can be called anywhere. Once all the data to be modified is modified, a digest method is called to calculate the hash code.

You can only calldigestMethod once. Before callingdigestThen, the messagedigest object is reset to the initial state.

You can freely implement the cloneable interface.instanceof CloneableTest reproducibility:

 

 MessageDigest md = MessageDigest.getInstance("SHA"); if (md instanceof Cloneable) {     md.update(toChapter1);     MessageDigest tc1 = md.clone();     byte[] toChapter1Digest = tc1.digest;     md.update(toChapter2);     ...etc. } else {     throw new DigestException("couldn't make digest of partial content"); } 

Note: If the given implementation is non-reproducible and the number of summaries is known in advance, several instances can still be used as examples to calculate the intermediate summary.

Constructor

Messagedigest

 protected MessageDigest(String algorithm)

Creates a message digest using the specified algorithm name.

 

Parameters:

Algorithm-standard string name of the digest algorithm. Appendix A of the API specification for the Java password structure. -->

Method

Getinstance

 public static MessageDigest getInstance(String algorithm) throws NoSuchAlgorithmException

Generates a messagedigest object that implements the specified Digest algorithm. If the default provider package contains a subclass that implements the messagedigest algorithm, an instance of this subclass is returned. If the algorithm is unavailable in the default package, other packages will be searched.

 

Parameters:

Algorithm-name of the applied algorithm. Appendix A of the API specification for the Java password structure. -->

Return Value:

A message digest object that implements the specified algorithm.

Throw:Nosuchalgorithmexception

If the algorithm is unavailable in the caller environment.

Getinstance

 public static MessageDigest getInstance(String algorithm,String provider) throwsNoSuchAlgorithmException,NoSuchProviderException

Generate a messagedigest object to implement the specified algorithm. If the provider's algorithm is available, the algorithm is provided by the provider.

 

Parameters:

Algorithm-name of the applied algorithm. Appendix A of the API specification for the Java password structure. -->

Provider-provider name.

Return Value:

A message digest object that implements the specified algorithm.

Throw:Nosuchalgorithmexception

If the algorithm is unavailable in the package provided by the caller.

Throw:Nosuchproviderexception

If the provider is unavailable in the environment.

See:

Provider

Update

 public void update(byte input)

Modify the Abstract With the specified byte.

 

Parameters:

Input-used to modify the bytes of the abstract.

Update

 public void update(byte input[],               int offset,                       int len)

Modify the Abstract With the specified byte array starting from the offset specified by the array.

 

Parameters:

Input-this byte array.

Offset-the offset starting from the byte array.

Len-slave offsetThe number of bytes.

Update

 public void update(byte input[])

Modify the Abstract With the specified byte array.

 

Parameters:

Input-this byte array.

Digest

 public byte[] digest()

The hash code is calculated by executing the final operations such as filling. Reset the summary after the call.

 

Return Value:

The byte array that stores the hash value of the result.

Digest

 public byte[] digest(byte input[])

Use the specified byte array to perform the last modification to the abstract, and then complete the summary calculation. That is, This method first calls update on the array and then calls Digest ().

 

Parameters:

Input-the input value used for modification before the summary calculation is complete.

Return Value:

The byte array of the result hash value.

Tostring

 public String toString()

Returns the string representation of the message digest object.

 

Overwrite:

Tostring in Class Object

Isequal

 public static boolean isEqual(byte digesta[],                               byte digestb[])

Compare whether the two summaries are the same. For a simple comparison.

 

Parameters:

Digesta-a summary to be compared.

Digestb-another abstract to be compared.

Return Value:

True if the two summaries are equal; otherwise, false.

Reset

 public void reset()

Reset the summary for future use.

A message digest is a digital fingerprint of a data block. Calculate a data block of any length and generate a unique fingerprint (for sha1, a 20-byte binary array ).

The message digest has two basic attributes:

It is difficult for two different packets to generate the same abstract.
It is difficult to generate a message for a specified digest, and the specified digest is calculated by the corresponding digest.
Representatives: sha1 of the National Institute of Standards and Technology and MD5.

Message Digest MD5 and Sha usage
Usage:

First, generate a messagedigest class to determine the calculation method.

Java. Security. messagedigest alga = java. Security. messagedigest. getinstance ("SHA-1 ");

Add the information of the digest to be calculated

Alga. Update (myinfo. getbytes ());

Calculate the abstract

Byte [] digesta = alga. Digest ();

Your information and summary sent to others

Other people initialize with the same method, add information, and finally compare the summary.

Algb. isequal (digesta, algb. Digest ())

Related AIP

Java. Security. messagedigest class

Static getinstance (string algorithm)

Returns a messagedigest object that implements the specified algorithm.

Parameter: algorithm name, such as SHA-1 or MD5

Void Update (byte input)

Void Update (byte [] input)

Void Update (byte [] input, int offset, int Len)

Add the information of the digest to be calculated

Byte [] Digest ()

After the calculation is completed, return the computed Summary (for MD5, 16 bits, and Sha, 20 bits)

Void reset ()

Reset

Static Boolean isequal (byte [] digesta, byte [] digestb)

Whether the two abstracts are the same

Code:
Import java. Security .*;

Public class mydigest {
Public static void main (string [] ARGs ){

Mydigest my = new mydigest ();
My. testdigest ();
}

Public void testdigest (){
Try {
String myinfo = "my test information ";

// Java. Security. messagedigest
// ALG = java. Security. messagedigest. getinstance ("MD5 ");
Java. Security. messagedigest alga = java. Security. messagedigest
. Getinstance ("SHA-1 ");
Alga. Update (myinfo. getbytes ());
Byte [] digesta = alga. Digest ();
System. Out. println ("This information abstract is:" + byte2hex (digesta ));
// You can pass your information (myinfo) and digest (digesta) to other people in a certain way to determine whether the information is changed or transmitted normally.
Java. Security. messagedigest algb = java. Security. messagedigest
. Getinstance ("SHA-1 ");
Algb. Update (myinfo. getbytes ());
If (algb. isequal (digesta, algb. Digest ())){
System. Out. println ("information check is normal ");
} Else {
System. Out. println ("different abstract ");
}

} Catch (Java. Security. nosuchalgorithmexception ex ){
System. Out. println ("invalid Digest algorithm ");
}

}

Public String byte2hex (byte [] B) // two-line conversion string
{
String HS = "";
String stmp = "";
For (INT n = 0; n <B. length; n ++ ){
Stmp = (Java. Lang. Integer. tohexstring (B [N] & 0xff ));
If (stmp. Length () = 1)
HS = HS + "0" + stmp;
Else
HS = HS + stmp;
}

Return HS. touppercase ();
}

}

B [N] & 0xff converts byte to int.

Because 0xff is an integer, byte [] B; B [Index] & 0xff is closer to the big data type, which is an integer.

The Byte in Java is sign, so the forced conversion of a negative byte to an int will damage the original binary representation, for example:
Byte BB = (byte) 0xf1; // 11110001
Printbinary (INT) bb); // 11111111111111111111111111110001

Printbinary (BB & 0xff); // 00000000000000000000000011110001

Running result:

INT:-15 binary:

11111111111111111111111111110001

INT: 241 binary:

00000000000000000000000011110001