iaik.security.rsa
Class RSAPublicKey

java.lang.Object
  |
  +--iaik.x509.PublicKeyInfo
        |
        +--iaik.security.rsa.RSAPublicKey

public class RSAPublicKey

extends PublicKeyInfo

implements RSAPublicKey, java.io.Serializable, java.lang.Cloneable

This class implements a RSA public key and supports ASN.1 encoding. This class extends iaik.x509.PublicKeyInfo for supporting RSA public keys to be used within X.509 certificates. This class implements the java.security.interfaces.RSAPublicKey interface for providing the functionality of a public key, as used for data encrypting or signature verifying based on the RSA algorithm.

PKCS#1 describes a X.509/PEM compatible syntax for RSA public keys to be used in certificates. The corresponding ASN.1 type RSAPublicKey is defined as ASN.1 SEQUENCE:

 RSAPublicKey ::= SEQUENCE {
   modulus INTEGER, -- n
   publicExponent INTEGER -- e }
 

An application wishing to create a RSAPublicKey to be used for, e.g. data encryption or signature verifying with the RSA algorithm, uses a proper getInstance method of the java.security.KeyPairGenerator class, which subsequently maybe casted to RSAKeyPairGenerator for performing an algorithm-specific initialization with proper RSA parameters. If an algorithm-specific initialization is not required, the cast to RSAKeyPairGenerator can be omitted.

Generally four steps have to be performed for creating a RSAPublicKey by using a proper KeyPairGenerator:

• First the KeyPairGenerator has to be instantiated thereby specifying the applicationīs intention to create keys for use within the RSA algorithm:

   KeyPairGenerator key_gen = KeyPairGenerator.getInstance("RSA");
   

• 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., 512 bits, this can be explicitly specified (when not initializing the generator explicitly, per default the modulus length is set to 1024 bits):

   key_gen.initialize(512);
   

• Third the key pair is created by calling generateKeyPair():

   KeyPair key_pair = key_gen.generateKeyPair();
   

• And finally, if there is need for the RSA public key, it has to be obtained from the key pair just created:

   RSAPublicKey rsa_pub_key = (RSAPublicKey)key_pair.getPublic();
   

For performing an algorithm-specific initialization with particular RSA parameters (e.g. using a particular public exponent e), an explicit cast of the KeyPairGenerator will be necessary for obtaining a specific RSAKeyPairGenerator to be initialized with the desired RSA parameters:

 RSAKeyPairGenerator rsa_key_gen = (RSAKeyPairGenerator)key_gen;
 rsa_key_gen.initialize(512, pub_exponent, sec_random);
 

(where sec_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/1.2/docs/guide/security/CryptoSpec.html.

See Also:

PublicKeyInfo, RSAPublicKey, KeyPairGenerator, KeyPair, iaik.pkcs.pkcs1.RSACipher, RSAKey, RSAPrivateKey, RSAKeyPairGenerator, RSAKeyFactory, Serialized Form

Fields inherited from class iaik.x509.PublicKeyInfo

public_key_algorithm

Fields inherited from interface java.security.PublicKey

serialVersionUID

Fields inherited from interface java.security.Key

serialVersionUID

Constructor Summary

RSAPublicKey(ASN1Object obj)
Creates a new RSAPublicKey from the given ASN.1 data structure representing a RSAPublicKey or PublicKeyInfo.

RSAPublicKey(java.math.BigInteger modulus, java.math.BigInteger publicExponent)
Creates a new RSAPublicKey with given values for the modulus n and the public exponent e.

RSAPublicKey(byte[] pk)
Creates a new RSAPublicKey from the given DER encoded byte array.

RSAPublicKey(java.io.InputStream is)
Creates a new RSAPublicKey from an InputStream.

RSAPublicKey(RSAPublicKey key)
Creates a new RSAPublicKey from the given RSAPublicKey representing modulus n and public exponent e.

RSAPublicKey(RSAPublicKeySpec keySpec)
Creates a new RSAPublicKey from the given RSAPublicKeySpec representing modulus n and public exponent e.

Method Summary

java.lang.Object	clone()
java.math.BigInteger	crypt(java.math.BigInteger message) Uses the public key to encrypt or decrypt a message.
protected void	decode(byte[] publicKey) Decodes a RSAPublicKey, encoded in DER format (PKCS#1).
protected byte[]	encode() Returns this RSA public key as DER encoded ASN.1 object (PKCS#1).
boolean	equals(java.lang.Object obj) Compares this public key to another public key.
java.lang.String	getAlgorithm() Returns the name of the appertaining algorithm.
byte[]	getFingerprint() Returns the fingerprint of this RSA public key.
java.math.BigInteger	getModulus() Returns the modulus of the public key.
java.math.BigInteger	getPublicExponent() Returns the public exponent of the public key.
int	hashCode() Returns a hash code for this object.
java.lang.String	toString() Returns a string that represents the contents of this RSA public key.

Methods inherited from class iaik.x509.PublicKeyInfo

createPublicKeyInfo, decode, getEncoded, getFormat, getPublicKey, getPublicKey, toASN1Object, writeTo

Methods inherited from class java.lang.Object

finalize, getClass, notify, notifyAll, wait, wait, wait

Constructor Detail

RSAPublicKey

public RSAPublicKey(java.math.BigInteger modulus,
                    java.math.BigInteger publicExponent)

Creates a new RSAPublicKey with given values for the modulus n and the public exponent e.

Parameters:

modulus - the modulus of the key

publicExponent - the public exponent of the key

RSAPublicKey

public RSAPublicKey(RSAPublicKeySpec keySpec)

Creates a new RSAPublicKey from the given RSAPublicKeySpec representing modulus n and public exponent e.

Parameters:

keySpec - the RSAPublicKeySpec representing modulus n and public exponent e

RSAPublicKey

public RSAPublicKey(RSAPublicKey key)

Creates a new RSAPublicKey from the given RSAPublicKey representing modulus n and public exponent e.

Parameters:

key - the RSAPublicKey representing modulus n and public exponent e

RSAPublicKey

public RSAPublicKey(byte[] pk)
             throws InvalidKeyException

Creates a new RSAPublicKey from the given DER encoded byte array.

This constructor may be used for parsing an already exisiting RSAPublicKey object, supplied as DER encoded byte array, which may have been created by calling the encode method.

Parameters:

the - byte array holding the DER encoded public key ASN.1 data structure

Throws:

InvalidKeyException - if something is wrong with the key encoding

RSAPublicKey

public RSAPublicKey(ASN1Object obj)
             throws InvalidKeyException

Creates a new RSAPublicKey from the given ASN.1 data structure representing a RSAPublicKey or PublicKeyInfo.

Parameters:

obj - the public key ASN.1 structure

Throws:

InvalidKeyException - if something is wrong with the key encoding

RSAPublicKey

public RSAPublicKey(java.io.InputStream is)
             throws java.io.IOException,
                    InvalidKeyException

Creates a new RSAPublicKey from an InputStream.

Parameters:

is - an input stream with the data to be read to initialize the public key

Throws:

java.io.IOException - if an I/O error occurs

InvalidKeyException - if something is wrong with the key encoding

Method Detail

decode

protected void decode(byte[] publicKey)
               throws InvalidKeyException

Decodes a RSAPublicKey, encoded in DER format (PKCS#1).

From the given DER encoded byte array an ASN.1 object is created and parsed for modulus n and public exponent e.

Overrides:

decode in class PublicKeyInfo

Parameters:

publicKey - the public key as DER encoded ASN.1 object

Throws:

InvalidKeyException - if something is wrong with the encoding of the key

encode

protected byte[] encode()

Returns this RSA public key as DER encoded ASN.1 object (PKCS#1). The ASN.1 type is "RSAPublicKey" and the coding is DER.

Overrides:

encode in class PublicKeyInfo

Returns:

a byte array holding the RSA public key as a DER encoded ASN.1 datastructure

crypt

public java.math.BigInteger crypt(java.math.BigInteger message)

Uses the public key to encrypt or decrypt a message. Simply performs a modulo exponentiation.

Parameters:

message - the message to en/decrypt as BigInteger

Returns:

the encrypted or decrypted message

getAlgorithm

public java.lang.String getAlgorithm()

Returns the name of the appertaining algorithm.

Overrides:

getAlgorithm in class PublicKeyInfo

Returns:

the string "RSA"

getPublicExponent

public java.math.BigInteger getPublicExponent()

Returns the public exponent of the public key.

Specified by:

getPublicExponent in interface RSAPublicKey

Returns:

the public exponent

getModulus

public java.math.BigInteger getModulus()

Returns the modulus of the public key.

Specified by:

getModulus in interface RSAPublicKey

Returns:

the modulus

getFingerprint

public byte[] getFingerprint()

Returns the fingerprint of this RSA public key. This is a MD5 hash of the DER encoded SubjectPublicKey.

Overrides:

getFingerprint in class PublicKeyInfo

Returns:

the fingerprint of this RSA public key

hashCode

public int hashCode()

Returns a hash code for this object.

Overrides:

hashCode in class java.lang.Object

Returns:

the hash code

toString

public java.lang.String toString()

Returns a string that represents the contents of this RSA public key.

Overrides:

toString in class PublicKeyInfo

Returns:

the string representation

equals

public boolean equals(java.lang.Object obj)

Description copied from class: PublicKeyInfo

Compares this public key to another public key. This method simply compares der DER encoded version of the keys.

Overrides:

equals in class PublicKeyInfo

Tags copied from class: PublicKeyInfo

Returns:

true, if the 2 public keys are equal, false otherwise

clone

public java.lang.Object clone()

Overrides:

clone in class java.lang.Object