DSAPublicKey ("Entrust Authority Security Toolkit for the Java Platform")

java.lang.Object
- iaik.x509.PublicKeyInfo
- - iaik.security.dsa.DSAPublicKey

All Implemented Interfaces:

ASN1Type, java.io.Serializable, java.security.interfaces.DSAKey, java.security.interfaces.DSAPublicKey, java.security.Key, java.security.PublicKey
```
public class DSAPublicKey
extends PublicKeyInfo
implements java.security.interfaces.DSAPublicKey, java.io.Serializable
```
An implementation of a DSA public key that supports ASN.1 encoding.
This class extends iaik.x509.PublicKeyInfo for supporting DSA public keys to be used within X.509 certificates . This class implements the java.security.interfaces.DSAPublicKey interface for providing the functionality of a public key used for verifying some signature within the DSA algorithm.
The Digital Signature Algorithm (DSA) only can be used for digital signing (respectively signature verifying). It cannot be used for data encryption.
The DSA algorithm uses a certain number of parameters:
- a prime number p, which length is a multiple of 64 bits lying between 512 and 1024 bits
- a 160-bit prime factor (q) of p-1
- a number h less than p-1 fulfilling (h^(p-1)/q)(mod p) > 1
- a number g calculated from g = (h^(p-1)/q)(mod p)
- a number x less than q
- a number y calculated from y = (g^x)(mod p)
p, q, g are made public, y forms the public key, and x represents the private key. The procedures of signing some message with one entity's private key, and verifying a signature using the signer's public key may be read up in "Applied Cryptography", Bruce Schneier, ISBN 0-471-59756-2).
An application wishing to create a DSAPublicKey to be used for signature verifying with the DSA algorithm, uses a proper getInstance method of the java.security.KeyPairGenerator class, which subsequently maybe casted to DSAKeyPairGenerator for performing an algorithm-specific initialization with proper DSA parameters. If an algorithm-specific initialization is not required, the cast to DSAKeyPairGenerator can be omitted.
Generally four steps have to be performed for creating a DSAPublicKey by using a proper KeyPairGenerator:
- First the KeyPairGenerator has to be instantiated thereby specifying the application's intention to create keys for use within the DSA algorithm:
```
 KeyPairGenerator key_gen = KeyPairGenerator.getInstance("DSA", "IAIK");
 
```
- Second, the KeyPairGenerator just created may be initialized using a proper initialize method. For initializing the generator to create keys with a modulus length of, e.g., 1024 bits, this can be explicitly specified (1024 bits also is the default value for the modulus length when not explicitly initializing the generator):
```
 key_gen.initialize(1024);
 
```
- Third the key pair is created by calling generateKeyPair():
```
 KeyPair key_pair = key_gen.generateKeyPair();
 
```
- And finally, if there is need for the DSA public key, it has to be obtained from the key pair just created:
```
 DSAPublicKey dsa_pub_key = (DSAPublicKey)key_pair.getPublic();
 
```
For performing an algorithm-specific initialization with particular DSA parameters (which may be an instance of DSAParams representing the public parameter values p, q and g), an explicit cast of the KeyPairGenerator will be necessary for obtaining a specific DSAKeyPairGenerator to be initialized with the desired DSA parameters:
```
 DSAKeyPairGenerator dsa_key_gen = (DSAKeyPairGenerator)key_gen;
 dsa_key_gen.initialize(dsa_params, random);
 
```
(where random denotes some random seed)
Guidelines on how to create some key using a KeyPairGenerator can be found in http://java.sun.com/products/JDK/1.1/docs/guide/security/CryptoSpec.html.
See Also:

PublicKeyInfo, DSAPublicKey, KeyPairGenerator, KeyPair, DSAPrivateKey, DSAKeyPairGenerator, DSAKeyFactory, DSAParams, Serialized Form

Field Summary
- Fields inherited from class iaik.x509.PublicKeyInfo
  public_key_algorithm
- Fields inherited from interface java.security.interfaces.DSAPublicKey
  serialVersionUID

Constructor Summary

Constructors
Constructor and Description
`DSAPublicKey(ASN1Object obj)` Creates a new DSAPublicKey from the given ASN.1 object.
`DSAPublicKey(java.math.BigInteger y, java.math.BigInteger p, java.math.BigInteger q, java.math.BigInteger g)` Creates a new DSAPublicKey from the given BigInteger values.
`DSAPublicKey(java.math.BigInteger y, java.security.interfaces.DSAParams dsaParams)` Creates a new DSAPublicKey from given public key value y and DSA parameters
`DSAPublicKey(byte[] key)` Creates a new DSAPublicKey from the given DER encoded ASN.1 data structure.
`DSAPublicKey(java.security.interfaces.DSAPublicKey pubKey)` Creates a new DSAPublicKey from the given DSAPublicKey.
`DSAPublicKey(java.security.spec.DSAPublicKeySpec keySpec)` Creates a new DSAPublicKey from the given DSAPublicKeySpec representing the DSA public key value y, and the public values p, q and g.
`DSAPublicKey(java.io.InputStream is)` Creates a new DSAPublicKey from an InputStream.

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`protected void`	`decode(byte[] publicKey)` Decodes a DSAPublicKey, encoded in DER format.
`protected byte[]`	`encode()` Returns this DSAPublicKey public key as DER encoded ASN.1 object.
`boolean`	`equals(java.lang.Object obj)` Compares this DSAPublicKey with the given DSAPublicKey.
`java.lang.String`	`getAlgorithm()` Returns the String "DSA"
`java.security.interfaces.DSAParams`	`getParams()` Returns the DSA parameters prime p, sub-prime q and base g as DSAParams.
`java.math.BigInteger`	`getY()` Returns the public key value y.
`int`	`hashCode()` Returns a hash code for this DSAPublicKey object.

Methods inherited from class iaik.x509.PublicKeyInfo
createPublicKeyInfo, decode, getEncoded, getFingerprint, getFormat, getPublicKey, getPublicKey, toASN1Object, toString, writeTo

Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface java.security.Key
getEncoded, getFormat

- Constructor Detail
  - DSAPublicKey
```
public DSAPublicKey(java.math.BigInteger y,
                    java.security.interfaces.DSAParams dsaParams)
```
    Creates a new DSAPublicKey from given public key value y and DSA parameters
    
    Parameters:
    
    y - the BigInteger value representing the DSA public key value
    
    dsaParams - the public DSA parameters p (prime), q (sub-prime) and g (base) as DSAParams
    
    See Also:
    
    DSAParams
  - DSAPublicKey
```
public DSAPublicKey(java.math.BigInteger y,
                    java.math.BigInteger p,
                    java.math.BigInteger q,
                    java.math.BigInteger g)
```
    Creates a new DSAPublicKey from the given BigInteger values.
    
    Parameters:
    
    y - the BigInteger value representing the DSA public key
    
    p - the public prime p (of a multiple length of 64 bits between 512 and 1024 bits)
    
    q - the public sub-prime q (a 160-bit prime factor of p-1)
    
    g - the public base g (=(h^(p-1)/q)(mod p) > 1, with h < p-1)
  - DSAPublicKey
```
public DSAPublicKey(java.security.spec.DSAPublicKeySpec keySpec)
```
    Creates a new DSAPublicKey from the given DSAPublicKeySpec representing the DSA public key value y, and the public values p, q and g.
    
    Parameters:
    
    keySpec - the DSAPublicKeySpec representing the public key value y, the prime p, the sub-prime q, and the base g
    
    See Also:
    
    DSAPublicKeySpec
  - DSAPublicKey
```
public DSAPublicKey(java.security.interfaces.DSAPublicKey pubKey)
```
    Creates a new DSAPublicKey from the given DSAPublicKey.
    
    Parameters:
    
    pubKey - the DSAPublicKey
  - DSAPublicKey
```
public DSAPublicKey(byte[] key)
             throws java.security.InvalidKeyException
```
    Creates a new DSAPublicKey from the given DER encoded ASN.1 data structure.
    This constructor may be used for parsing an already exisiting DSA public key, wrapped into a X.509 PublicKeyInfo that is supplied as DER encoded byte array.
    
    Parameters:
    
    key - the byte array holding the DER encoded public key info
    
    Throws:
    
    java.security.InvalidKeyException - if something is wrong with the key encoding
  - DSAPublicKey
```
public DSAPublicKey(ASN1Object obj)
             throws java.security.InvalidKeyException
```
    Creates a new DSAPublicKey from the given ASN.1 object. The supplied ASN1Object represents a X.509 PublicKeyInfo holding the DSA public key.
    
    Parameters:
    
    obj - the public key ASN.1 data structure
    
    Throws:
    
    java.security.InvalidKeyException - if something is wrong with the key encoding
  - DSAPublicKey
```
public DSAPublicKey(java.io.InputStream is)
             throws java.security.InvalidKeyException,
                    java.io.IOException
```
    Creates a new DSAPublicKey from an InputStream.
    This constructor may be used for parsing an already exisiting DH public key, wrapped into a X.509 PublicKeyInfo that is supplied as DER encoded byte array.
    
    Parameters:
    
    is - the input stream with the data to be read to initialize the public key
    
    Throws:
    
    java.security.InvalidKeyException - if something is wrong with the key encoding
    
    java.io.IOException - if something is wrong with the file
- Method Detail
  - getY
```
public java.math.BigInteger getY()
```
    Returns the public key value y.
    
    Specified by:
    
    getY in interface java.security.interfaces.DSAPublicKey
    
    Returns:
    
    the public key value y
  - getParams
```
public java.security.interfaces.DSAParams getParams()
```
    Returns the DSA parameters prime p, sub-prime q and base g as DSAParams.
    
    Specified by:
    
    getParams in interface java.security.interfaces.DSAKey
    
    Returns:
    
    the DSAParams representing prime p, sub-prime q and base g
  - getAlgorithm
```
public java.lang.String getAlgorithm()
```
    Returns the String "DSA"
    
    Specified by:
    
    getAlgorithm in interface java.security.Key
    
    Specified by:
    
    getAlgorithm in class PublicKeyInfo
    
    Returns:
    
    the name of the algorithm
  - decode
```
protected void decode(byte[] publicKey)
               throws java.security.InvalidKeyException
```
    Decodes a DSAPublicKey, encoded in DER format.
    This method is protected and typically will not be used by an application. Rather it is used by the parent X.509 PublicKeyInfo class for decoding the inherent DSA public key.
    
    Specified by:
    
    decode in class PublicKeyInfo
    
    Parameters:
    
    publicKey - the public key as DER encoded ASN.1 object
    
    Throws:
    
    java.security.InvalidKeyException - if the given key is not a DSA public key
  - encode
```
protected byte[] encode()
```
    Returns this DSAPublicKey public key as DER encoded ASN.1 object.
    This method is protected and typically will not be used by an application. Rather it is used by the parent X.509 PublicKeyInfo class for encoding the inherent DSA public key.
    
    Specified by:
    
    encode in class PublicKeyInfo
    
    Returns:
    
    this DSAPublicKey as DER encoded ASN.1 data structure
  - hashCode
```
public int hashCode()
```
    Returns a hash code for this DSAPublicKey object.
    
    Overrides:
    
    hashCode in class java.lang.Object
    
    Returns:
    
    the hash code
  - equals
```
public boolean equals(java.lang.Object obj)
```
    Compares this DSAPublicKey with the given DSAPublicKey.
    
    Overrides:
    
    equals in class PublicKeyInfo
    
    Parameters:
    
    obj - the other DSAPublicKey
    
    Returns:
    
    true, if the two public key objects are equal, false otherwise

Class DSAPublicKey

Field Summary

Fields inherited from class iaik.x509.PublicKeyInfo

Fields inherited from interface java.security.interfaces.DSAPublicKey

Constructor Summary

Method Summary

Methods inherited from class iaik.x509.PublicKeyInfo

Methods inherited from class java.lang.Object

Methods inherited from interface java.security.Key

Constructor Detail

DSAPublicKey

DSAPublicKey

DSAPublicKey

DSAPublicKey

DSAPublicKey

DSAPublicKey

DSAPublicKey

Method Detail

getY

getParams

getAlgorithm

decode

encode

hashCode

equals