crypto
Class AsymmetricCipher

java.lang.Object
  crypto.AsymmetricCipher

public class AsymmetricCipher
extends java.lang.Object

Implements asymmetric cipher with public and private keys used to retrieve secret key (used for symmetric ciphering of peer-to-peer datagram packets) from remote peer. Remote peer sends its secret key encrypted with our public key. Transmission of the SecretKey can be schematically shown:

  Send secret key:
  secretKey >> serialize >> encrypt (with PubKey) >> encode to Base64 >> transmit
  
  Reconstruct secret key:
  receive >> decode from Base64 >> decrypt (with PrivKey) >> deserialize >> secretKey
  

Author:

Mikica B Kocic

Field Summary

private static java.lang.String	algorithm Asymmetric cipher algorithm
private javax.crypto.Cipher	cipher Instance of the decrypting engine based on our private key
private static java.lang.String	digest Message digest used for creating/validating signatures
private java.lang.String	keyPairComment The comment (description) of the key pair
private static int	keySize Default key size for algorithm
private static java.lang.String	padding Padding to be used when ciphering/deciphering.
private java.security.PrivateKey	privateKey Private key used for deciphering and signing messages
private static java.lang.String	privateKeyFile The name of the file holding saved private key
private java.security.PublicKey	publicKey Public key corresponding to our private key
private static java.lang.String	publicKeyFile The name of the file holding saved public key
private java.lang.String	serializedPublicKey Our public key: serialized and encoded as Base64 string.

Constructor Summary

AsymmetricCipher()
Generates a pair of keys and serializes public key as Base64 string.

Method Summary

byte[]	decrypt(byte[] cipherText) Decrypts cipher text using the private key.
SymmetricCipher	deserializeEncryptedSecretKey(java.lang.String serializedSecretKey) Reconstructs secret key from Base64 respresentation of encrypted (using our public key) serialized secret key.
private void	destruct() Destructs object (makes it inactive)
void	exportPublicKey(java.lang.String fileName) Save public key into file
private void	generateKeyPair() Generates a key pair
java.lang.String	getNamedPublicKey() Returns serializable named publicKey (with comment) encoded as Base64
java.lang.String	getSerializedAndSignedPublicKey() Returns serialized public key used for encryption of datagrams as Base64 string.
private void	instantiateCipher() Instantiates a cipher
boolean	isActive() Returns if cipher is properly initialized
static java.lang.Object	loadObject(java.lang.String fileName) Loads serializable object encoded in Base64 from file
private boolean	loadSavedKeyPair() Load saved key pair
private boolean	sanityCheck() Sanity check whether PublicEncryptor works with PrivateEncryption
private void	saveKeyPair() Saves private/public key pair with description (this.keyPairComment)
static boolean	saveObject(java.io.Serializable object, java.lang.String fileName, java.lang.String comment) Saves serializable object encoded in Base64 to file
private void	serializePublicKey() Serializes the public key, signs it and encodes in Base64 format
java.security.SignedObject	signObject(java.io.Serializable object) Signs object using private key

Methods inherited from class java.lang.Object

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

Field Detail

algorithm

private static final java.lang.String algorithm

Asymmetric cipher algorithm

See Also:

Constant Field Values

keySize

private static final int keySize

Default key size for algorithm

See Also:

Constant Field Values

padding

private static final java.lang.String padding

Padding to be used when ciphering/deciphering. JCE does not support RSA/CBC so the CBC mode is built on the top of ECB in AsymmetricCipher.decrypt().

See Also:

Constant Field Values

digest

private static final java.lang.String digest

Message digest used for creating/validating signatures

See Also:

Constant Field Values

privateKeyFile

private static final java.lang.String privateKeyFile

The name of the file holding saved private key

See Also:

Constant Field Values

publicKeyFile

private static final java.lang.String publicKeyFile

The name of the file holding saved public key

See Also:

Constant Field Values

privateKey

private java.security.PrivateKey privateKey

Private key used for deciphering and signing messages

publicKey

private java.security.PublicKey publicKey

Public key corresponding to our private key

keyPairComment

private java.lang.String keyPairComment

The comment (description) of the key pair

cipher

private javax.crypto.Cipher cipher

Instance of the decrypting engine based on our private key

serializedPublicKey

private java.lang.String serializedPublicKey

Our public key: serialized and encoded as Base64 string.

Constructor Detail

AsymmetricCipher

public AsymmetricCipher()

Generates a pair of keys and serializes public key as Base64 string.

Method Detail

destruct

private void destruct()

Destructs object (makes it inactive)

loadSavedKeyPair

private boolean loadSavedKeyPair()

Load saved key pair

saveKeyPair

private void saveKeyPair()

Saves private/public key pair with description (this.keyPairComment)

generateKeyPair

private void generateKeyPair()

Generates a key pair

instantiateCipher

private void instantiateCipher()

Instantiates a cipher

serializePublicKey

private void serializePublicKey()

Serializes the public key, signs it and encodes in Base64 format

isActive

public boolean isActive()

Returns if cipher is properly initialized

getSerializedAndSignedPublicKey

public java.lang.String getSerializedAndSignedPublicKey()

Returns serialized public key used for encryption of datagrams as Base64 string.

exportPublicKey

public void exportPublicKey(java.lang.String fileName)

Save public key into file

Parameters:

fileName - file where to save public key; if null, it will be the default: AssymmetricCipher.publicKeyFile

getNamedPublicKey

public java.lang.String getNamedPublicKey()

Returns serializable named publicKey (with comment) encoded as Base64

saveObject

public static boolean saveObject(java.io.Serializable object,
                                 java.lang.String fileName,
                                 java.lang.String comment)

Saves serializable object encoded in Base64 to file

loadObject

public static java.lang.Object loadObject(java.lang.String fileName)

Loads serializable object encoded in Base64 from file

sanityCheck

private boolean sanityCheck()

Sanity check whether PublicEncryptor works with PrivateEncryption

decrypt

public byte[] decrypt(byte[] cipherText)

Decrypts cipher text using the private key. Emulates CBC (cipher-block chaining) using plain ECB. Why? -- Because JCE does not support RSA/CBC cipher (only RSA/ECB). See Cipher-block chaining (CBC) \image html cbc_decryption.png

See Also:

PublicEncryptor.encrypt(byte[])

signObject

public java.security.SignedObject signObject(java.io.Serializable object)

Signs object using private key

deserializeEncryptedSecretKey

public SymmetricCipher deserializeEncryptedSecretKey(java.lang.String serializedSecretKey)

Reconstructs secret key from Base64 respresentation of encrypted (using our public key) serialized secret key.