org.jnetpcap.util.checksum
Class Checksum

java.lang.Object
  org.jnetpcap.util.checksum.Checksum

public class Checksum
extends java.lang.Object

Main base and utility class that provides native methods for calculating various CRC on buffers.

Author:

Mark Bednarczyk, Sly Technologies, Inc.

Constructor Summary

Checksum()

Method Summary

static int	crc16CCITT(JBuffer buffer, int offset, int length) Calculate CCITT CRC16 checksum using a CRC32 CCITT seed.
static int	crc16CCITTContinue(JBuffer buffer, int offset, int length, int crc) Calculate CCITT 16-bit checksum using a partially calculated CRC16.
static int	crc16CCITTSeed(JBuffer buffer, int offset, int length, int seed) Calculate CCITT 16-bit checksum using a custom seed.
static int	crc16X25CCITT(JBuffer buffer, int offset, int length) Calculate CCITT CRC16 X.25 checksum using a CCITT seed.
static int	crc32c(JBuffer buffer, int offset, int length, int crc) Calculate a standard CRC32C checksum using a custom seed.
static long	crc32CCITT(JBuffer buffer, int offset, int length) Calculate CCITT CRC32 checksum using a CRC32 CCITT seed.
static int	crc32CCITTContinue(JBuffer buffer, int offset, int length, int crc) Calculate a standard CRC32C checksum using a partially calculated CRC32.
static int	crc32CCITTSeed(JBuffer buffer, int offset, int length, int seed) Calculate CCITT CRC32 checksum using a custom seed.
static long	crc32IEEE802(JBuffer buffer, int offset, int length) Calculates IEEE 802 based checksums including ethernet/802.3.
static long	flip(long c) Flips the bytes from LITTLE to BIG ENDIAN.
static int	icmp(JBuffer buffer, int ipOffset, int icmpOffset) Icmp.
static int	inChecksum(JBuffer buffer, int offset, int length) Calculate a CRC16 using one's complement of one's complement algorithm.
static int	inChecksumShouldBe(int checksum, int calculateChecksum) Computes what the checksum should be based on calculated checksum and the checksum in the header's checksum field.
static int	pseudoTcp(JBuffer buffer, int ipOffset, int tcpOffset) Pseudo tcp.
static int	pseudoUdp(JBuffer buffer, int ipOffset, int udpOffset) Pseudo udp.

Methods inherited from class java.lang.Object

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

Constructor Detail

Checksum

public Checksum()

Method Detail

crc16CCITT

public static int crc16CCITT(JBuffer buffer,
                             int offset,
                             int length)

Calculate CCITT CRC16 checksum using a CRC32 CCITT seed.

Parameters:

buffer - buffer to calculate crc on

offset - offset into the buffer

length - length within the buffer

Returns:

calculated crc

crc16CCITTContinue

public static int crc16CCITTContinue(JBuffer buffer,
                                     int offset,
                                     int length,
                                     int crc)

Calculate CCITT 16-bit checksum using a partially calculated CRC16.

Parameters:

buffer - buffer to calculate crc on

offset - offset into the buffer

length - length within the buffer

crc - the preload value for the CRC16 computation

Returns:

calculated crc

crc16CCITTSeed

public static int crc16CCITTSeed(JBuffer buffer,
                                 int offset,
                                 int length,
                                 int seed)

Calculate CCITT 16-bit checksum using a custom seed.

Parameters:

buffer - buffer to calculate crc on

offset - offset into the buffer

length - length within the buffer

seed - starting seed

Returns:

calculated crc

crc16X25CCITT

public static int crc16X25CCITT(JBuffer buffer,
                                int offset,
                                int length)

Calculate CCITT CRC16 X.25 checksum using a CCITT seed.

Parameters:

buffer - buffer to calculate crc on

offset - offset into the buffer

length - length within the buffer

Returns:

calculated crc

crc32c

public static int crc32c(JBuffer buffer,
                         int offset,
                         int length,
                         int crc)

Calculate a standard CRC32C checksum using a custom seed.

Parameters:

buffer - buffer to calculate crc on

offset - offset into the buffer

length - length within the buffer

crc - the preload value for the CRC32C computation

Returns:

calculated crc

crc32CCITT

public static long crc32CCITT(JBuffer buffer,
                              int offset,
                              int length)

Calculate CCITT CRC32 checksum using a CRC32 CCITT seed.

Parameters:

buffer - buffer to calculate crc on

offset - offset into the buffer

length - length within the buffer

Returns:

calculated crc

crc32CCITTContinue

public static int crc32CCITTContinue(JBuffer buffer,
                                     int offset,
                                     int length,
                                     int crc)

Calculate a standard CRC32C checksum using a partially calculated CRC32.

Parameters:

buffer - buffer to calculate crc on

offset - offset into the buffer

length - length within the buffer

crc - the preload value for the CRC32 computation

Returns:

calculated crc

crc32CCITTSeed

public static int crc32CCITTSeed(JBuffer buffer,
                                 int offset,
                                 int length,
                                 int seed)

Calculate CCITT CRC32 checksum using a custom seed.

Parameters:

buffer - buffer to calculate crc on

offset - offset into the buffer

length - length within the buffer

seed - starting seed

Returns:

calculated crc

crc32IEEE802

public static long crc32IEEE802(JBuffer buffer,
                                int offset,
                                int length)

Calculates IEEE 802 based checksums including ethernet/802.3.

Parameters:

buffer - buffer to calculate for

offset - offset into the buffer in bytes

length - number of bytes to run calculation on

Returns:

calculated checksum

flip

public static long flip(long c)

Flips the bytes from LITTLE to BIG ENDIAN. For example 0x01020304 becomes 0x04030201.

Parameters:

c - source value

Returns:

converted value

icmp

public static int icmp(JBuffer buffer,
                       int ipOffset,
                       int icmpOffset)

Icmp.

Parameters:

buffer - the buffer

ipOffset - the ip offset

icmpOffset - the icmp offset

Returns:

the int

inChecksum

public static int inChecksum(JBuffer buffer,
                             int offset,
                             int length)

Calculate a CRC16 using one's complement of one's complement algorithm. This method computes the CRC16 on a single buffer chunk.

Parameters:

buffer - buffer to reach the chunk of data

offset - offset into the buffer

length - number of bytes to include in calculation

Returns:

computed CRC16

inChecksumShouldBe

public static int inChecksumShouldBe(int checksum,
                                     int calculateChecksum)

Computes what the checksum should be based on calculated checksum and the checksum in the header's checksum field.

Parameters:

checksum - checksum within the header's field

calculateChecksum - checksum that was calculated

Returns:

resulting checksum of the combination of the 2

pseudoTcp

public static int pseudoTcp(JBuffer buffer,
                            int ipOffset,
                            int tcpOffset)

Pseudo tcp.

Parameters:

buffer - the buffer

ipOffset - the ip offset

tcpOffset - the tcp offset

Returns:

the int

pseudoUdp

public static int pseudoUdp(JBuffer buffer,
                            int ipOffset,
                            int udpOffset)

Pseudo udp.

Parameters:

buffer - the buffer

ipOffset - the ip offset

udpOffset - the udp offset

Returns:

the int