de.flexiprovider.core.rsa
Class RSA_PKCS1_v2_1

java.lang.Object
  |
  +--javax.crypto.CipherSpi
        |
        +--de.flexiprovider.api.Cipher
              |
              +--de.flexiprovider.api.AsymmetricBlockCipher
                    |
                    +--de.flexiprovider.core.rsa.RSA_PKCS1_v2_1

public class RSA_PKCS1_v2_1

extends AsymmetricBlockCipher

This class implements the RSA algorithm as defined in PKCS#1 version 2.1 in the OAEP (Optimal Asymmetric Encryption Padding) mode. The OAEP mode is recommended for new applications.

To encrypt a message, the following steps have to be performed:

 // The message to encrypt
 String message = "secret message";
 byte[] messageBytes = message.getBytes();
 
 // The source of randomness
 SecureRandom secureRandom = Registry.getSecureRandom();
 
 // Obtain a RSA Cipher Object
 Cipher rsaCipher = Cipher.getInstance("RSA_PKCS1_v2_1");
 
 // Obtain the corresponding key pair generator
 KeyPairGenerator rsaKPG = KeyPairGenerator.getInstance("RSA");
 
 // Initialize the key pair generator with the desired strength
 rsaKPG.initialize(1024);
 
 // Generate a key pair
 KeyPair rsaKeyPair = rsaKPG.genKeyPair();
 
 // Initialize the cipher
 // Note: if the public key has n with k(k - the length of n in octets) less than the 
 // HEADER_SIZE of RSA_PKCS1_v1_5, a RuntimeException is thrown.
 cipher.init(Cipher.ENCRYPT_MODE, rsaKeyPair.getPublic(), secureRandom);
 
 // Finally encrypt the message
 // If some of the PKCS1 functions fail during encryption, a RuntimeException is thrown.
 byte[] ciphertextBytes = cipher.doFinal(messageBytes);
 

To decrypt a ciphertext, the Cipher must be initialized with Cipher.DECRYPT_MODE and the private key (rsaKeyPair.getPrivate()). Decrypting, there are some special cases one should take in consideration:
1. If the length of the input is not equal to the maximum cipher text length. A RuntimeException is thrown and the decryption is aborted.
2. If some of the PKCS1 functions fail during encryption, a RuntimeException is thrown.

Author:

Thomas Wahrenbruch, Ralf-Philipp Weinmann

Field Summary

static java.lang.String

OID The OID of RSA_PKCS1_v2_1.

Fields inherited from class de.flexiprovider.api.AsymmetricBlockCipher

buf, cipherTextSize, maxPlainTextSize, paramSpec

Fields inherited from class de.flexiprovider.api.Cipher

DECRYPT_MODE, ENCRYPT_MODE, opMode

Constructor Summary

RSA_PKCS1_v2_1()

Method Summary

int	getKeySize(Key key) Returns the key size of the given key object.
java.lang.String	getName()
protected void	initCipherDecrypt(Key key, AlgorithmParameterSpec params) This method initializes the block cipher with a certain key and parameters for data encryption.
protected void	initCipherEncrypt(Key key, AlgorithmParameterSpec params, SecureRandom secureRandom) This method initializes the block cipher with a certain key and parameters for data encryption.
protected byte[]	messageDecrypt(byte[] input) Decrypt a ciphertext.
protected byte[]	messageEncrypt(byte[] input) Encrypt a message.

Methods inherited from class de.flexiprovider.api.AsymmetricBlockCipher

checkLength, doFinal, doFinal, getBlockSize, getIV, getOutputSize, getParameters, initDecrypt, initDecrypt, initEncrypt, initEncrypt, initEncrypt, initEncrypt, setMode, setPadding, update, update

Methods inherited from class de.flexiprovider.api.Cipher

doFinal, doFinal, engineDoFinal, engineDoFinal, engineGetBlockSize, engineGetIV, engineGetKeySize, engineGetOutputSize, engineGetParameters, engineInit, engineInit, engineInit, engineSetMode, engineSetPadding, engineUpdate, engineUpdate, update

Methods inherited from class java.lang.Object

, clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

OID

public static final java.lang.String OID

The OID of RSA_PKCS1_v2_1.

Constructor Detail

RSA_PKCS1_v2_1

public RSA_PKCS1_v2_1()

Method Detail

getName

public java.lang.String getName()

Overrides:

getName in class Cipher

Returns:

the name of this cipher

getKeySize

public int getKeySize(Key key)
               throws InvalidKeyException

Returns the key size of the given key object. Checks whether the key object is an instance of RSAPublicKey or RSAPrivateKey. Would be simpler to just check for RSAKey but this breaks build with Java 1.2.

Overrides:

getKeySize in class Cipher

Parameters:

key - the key object

Returns:

the key size of the given key object.

Throws:

InvalidKeyException - if key is invalid.

initCipherEncrypt

protected void initCipherEncrypt(Key key,
                                 AlgorithmParameterSpec params,
                                 SecureRandom secureRandom)
                          throws InvalidKeyException

This method initializes the block cipher with a certain key and parameters for data encryption.

Overrides:

initCipherEncrypt in class AsymmetricBlockCipher

Parameters:

key - the key which has to be used to encrypt data

params - the algorithm parameters

secureRandom - the source of randomness

Throws:

InvalidKeyException - if the given key is inappropriate for initializing this cipher.

initCipherDecrypt

protected void initCipherDecrypt(Key key,
                                 AlgorithmParameterSpec params)
                          throws InvalidKeyException

This method initializes the block cipher with a certain key and parameters for data encryption.

Overrides:

initCipherDecrypt in class AsymmetricBlockCipher

Parameters:

key - the key which has to be used to decrypt data

params - the algorithm parameters

Throws:

InvalidKeyException - if the given key is inappropriate for initializing this cipher.

messageEncrypt

protected byte[] messageEncrypt(byte[] input)

Encrypt a message.

Overrides:

messageEncrypt in class AsymmetricBlockCipher

Parameters:

input - the plaintext

Returns:

the encrypted plaintext

messageDecrypt

protected byte[] messageDecrypt(byte[] input)

Decrypt a ciphertext.

Overrides:

messageDecrypt in class AsymmetricBlockCipher

Parameters:

input - the ciphertext

Returns:

the decrypted ciphertext