com.github.davidcarboni.cryptolite

Class KeyExchange

java.lang.Object

com.github.davidcarboni.cryptolite.KeyExchange

public class KeyExchange
extends Object

This class provides for key exchange, using public-private key encryption (also known as asymmetric encryption). The algorithm used is "RSA", with padding CIPHER_PADDING, giving a Cipher name of CIPHER_NAME. This class allows you to encrypt a SecretKey so that it can be securely sent to another user. This is done using the destination user's PublicKey so that the recipient can decrypt it using their PrivateKey. Public-private key cryptography is not suitable for bulk encryption of data, (such as text and documents) so if you need to send encrypted data from one user to another, the process for this is slightly different, using both public-private and secret key encryption. If you wish to do this, you need to use something along the lines of the following:

• Encrypt the data being transmitted with a SecretKey, using the Crypto class.
• Encrypt the SecretKey using the destination user's PublicKey by calling encryptKey(SecretKey, PublicKey).
• Send the encrypted SecretKey to the destination user with the encrypted data.
• Use the destination user's PrivateKey to decrypt the SecretKey, by calling decryptKey(String, PrivateKey).
• The destination user can then use the recovered SecretKey to decrypt the data, using the Crypto class.

This solves the problem of securely exchanging a SecretKey so that two parties can use the same key to encrypt and decrypt data. Another approach is to use "key agreement", but this is currently beyond the scope of Cryptolite.

Author:

David Carboni

Field Summary

Fields

Modifier and Type	Field and Description
static String	CIPHER_ALGORITHM The name of the cipher algorithm to use for asymmetric cryptographic operations.
static String	CIPHER_MODE The name of the cipher mode to use for asymmetric cryptographic operations.
static String	CIPHER_PADDING The name of the padding type to use for asymmetric cryptographic operations.

Constructor Summary

Constructors

Modifier	Constructor and Description
	KeyExchange() Initialises the instance with the recommended setting of .
protected	KeyExchange(String cipherName) This constructor is protected so that, should you need a different algorithm (e.g.

Method Summary

Modifier and Type	Method and Description
SecretKey	decryptKey(String encryptedKey, PrivateKey privateKey) This method decrypts the given encrypted SecretKey using our PrivateKey.
String	encryptKey(SecretKey key, PublicKey destinationPublicKey) This method encrypts the given SecretKey with the destination user's PublicKey so that it can be safely sent to them.

Methods inherited from class java.lang.Object

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

Field Detail

CIPHER_ALGORITHM

public static final String CIPHER_ALGORITHM

The name of the cipher algorithm to use for asymmetric cryptographic operations.

See Also:

Constant Field Values

CIPHER_MODE

public static final String CIPHER_MODE

The name of the cipher mode to use for asymmetric cryptographic operations.

See Also:

Constant Field Values

CIPHER_PADDING

public static final String CIPHER_PADDING

The name of the padding type to use for asymmetric cryptographic operations.

See Also:

Constant Field Values

Constructor Detail

KeyExchange

public KeyExchange()

Initialises the instance with the recommended setting of .

KeyExchange

protected KeyExchange(String cipherName)

This constructor is protected so that, should you need a different algorithm (e.g. if you're integrating with a system that uses different crypto settings) it is possible to create a subclass with different settings.

Parameters:

cipherName - This should normally be .

Method Detail

encryptKey

public String encryptKey(SecretKey key,
                         PublicKey destinationPublicKey)

This method encrypts the given SecretKey with the destination user's PublicKey so that it can be safely sent to them.

Parameters:

key - The SecretKey to be encrypted.

destinationPublicKey - The PublicKey of the user to whom you will be sending the SecretKey. This can be obtained via Keys.newKeyPair().

Returns:

The encrypted key, as a base64-encoded String, suitable for passing to decryptKey(String, PrivateKey).

decryptKey

public SecretKey decryptKey(String encryptedKey,
                            PrivateKey privateKey)

This method decrypts the given encrypted SecretKey using our PrivateKey.

Parameters:

encryptedKey - The encrypted key as a base64-encoded string, as returned by encryptKey(SecretKey, PublicKey).

privateKey - The PrivateKey to be used to decrypt the encrypted key. This can be obtained via Keys.newKeyPair().

Returns:

The decrypted SecretKey.