org.eclipse.californium.scandium.dtls.cipher

Class CbcBlockCipher

java.lang.Object

org.eclipse.californium.scandium.dtls.cipher.CbcBlockCipher

public class CbcBlockCipher
extends Object

A cbc block cipher.

Constructor Summary

Constructors

Constructor and Description
CbcBlockCipher()

Method Summary

Methods

Modifier and Type	Method and Description
static boolean	checkPadding(int padding, byte[] data, int offset) Check padding.
static byte[]	decrypt(CipherSuite suite, SecretKey key, SecretKey macKey, byte[] additionalData, byte[] ciphertext) Converts a given TLSCiphertext.fragment to a TLSCompressed.fragment structure as defined by RFC 5246, section 6.2.3.2:
static byte[]	encrypt(CipherSuite suite, SecretKey key, SecretKey macKey, byte[] additionalData, byte[] payload) Converts a given TLSCompressed.fragment to a TLSCiphertext.fragment structure as defined by RFC 5246, section 6.2.3.2
static byte[]	getBlockCipherMac(Mac hmac, SecretKey macKey, byte[] additionalData, byte[] content, int length) Calculates a MAC for use with CBC block ciphers as specified by RFC 5246, section 6.2.3.2.

Methods inherited from class java.lang.Object

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

Constructor Detail

CbcBlockCipher

public CbcBlockCipher()

Method Detail

decrypt

public static byte[] decrypt(CipherSuite suite,
             SecretKey key,
             SecretKey macKey,
             byte[] additionalData,
             byte[] ciphertext)
                      throws GeneralSecurityException

Converts a given TLSCiphertext.fragment to a TLSCompressed.fragment structure as defined by RFC 5246, section 6.2.3.2:

 struct {
    opaque IV[SecurityParameters.record_iv_length];
    block-ciphered struct {
       opaque content[TLSCompressed.length];
       opaque MAC[SecurityParameters.mac_length];
       uint8 padding[GenericBlockCipher.padding_length];
       uint8 padding_length;
    };
 } GenericBlockCipher;
 

The particular cipher to use is determined from the negotiated cipher suite in the current DTLS connection state.

Parameters:

suite - used cipher suite

key - encryption key

macKey - mac key

additionalData - additional data. Note: the TLSCompressed.length is not available before decryption. Therefore the last two bytes will be modified with that length after the decryption.

ciphertext - encrypted message including initial vector

Returns:

decrypted and authenticated payload.

Throws:

InvalidMacException - if message authentication failed

GeneralSecurityException - if the ciphertext could not be decrypted

encrypt

public static byte[] encrypt(CipherSuite suite,
             SecretKey key,
             SecretKey macKey,
             byte[] additionalData,
             byte[] payload)
                      throws GeneralSecurityException

Converts a given TLSCompressed.fragment to a TLSCiphertext.fragment structure as defined by RFC 5246, section 6.2.3.2

 struct {
    opaque IV[SecurityParameters.record_iv_length];
    block-ciphered struct {
       opaque content[TLSCompressed.length];
       opaque MAC[SecurityParameters.mac_length];
       uint8 padding[GenericBlockCipher.padding_length];
       uint8 padding_length;
    };
 } GenericBlockCipher;
 

The particular cipher to use is determined from the negotiated cipher suite in the current DTLS connection state.

Parameters:

suite - used cipher suite

key - encryption key

macKey - mac key

additionalData - additional data

payload - message to encrypt

Returns:

encrypted message including initial vector

Throws:

GeneralSecurityException - if the plaintext could not be encrypted

getBlockCipherMac

public static byte[] getBlockCipherMac(Mac hmac,
                       SecretKey macKey,
                       byte[] additionalData,
                       byte[] content,
                       int length)
                                throws InvalidKeyException

Calculates a MAC for use with CBC block ciphers as specified by RFC 5246, section 6.2.3.2.

Parameters:

hmac - mac function

macKey - mac key

additionalData - additional data

content - payload

length - length of payload to be used

Returns:

mac bytes

Throws:

InvalidKeyException - if the mac keys doesn't fit the mac

checkPadding

public static boolean checkPadding(int padding,
                   byte[] data,
                   int offset)

Check padding. The check is implemented using a "time constant" approach by always comparing 256 bytes.

Parameters:

padding - padding to be checked

data - data to be checked. Must contain at least 256 + 1 bytes from the offset on. The value of the last byte will be changed!

offset - offset of the padding field.

Returns:

true, if padding bytes in data from the offset on contains the value of the padding byte.

Throws:

IllegalArgumentException - if the data array doesn't contain 257 bytes after the offset.