Package de.wuespace.telestion.extension.mavlink.security

Class X25Checksum

java.lang.Object
de.wuespace.telestion.extension.mavlink.security.X25Checksum
public final class X25Checksum extends Object
This class is handling the creation of the X.25 (CRC-16-CCITT) custom checksum for MAVLink.
Apart from only hashing the message itself a CRC_EXTRA byte must be added which is unique for each message. Only 2 bytes (last 2 bytes) of the final hash will then be used.

Implementation is based on the official c implementation for MAVLink.

  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    static int
    INIT_CRC
    Initial value for the CRC-Calculation.
    This is needed because for each byte of the message the current-checksum gets "reused".

  • Method Summary

    Modifier and Type
    Method
    Description
    static int
    calculate​(byte[] buffer)
    Calculates the CRC X.25-checksum for a whole byte[] array.
    Must contain the CRC_EXTRA byte which must be added for each message.
    static int
    calculate​(byte[] payload, int crc)
    Calculates the CRC X.25-checksum for a given payload array and the right crc-extra extra byte.
    static int
    calculate​(int data, int currentCrc)
    Calculates the CRC X.25-checksum for one byte with regards to the current-checksum.

    Methods inherited from class java.lang.Object

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

  • Field Details

    • INIT_CRC

      public static final int INIT_CRC
      Initial value for the CRC-Calculation.
      This is needed because for each byte of the message the current-checksum gets "reused".
      See Also:
      Constant Field Values

  • Method Details

    • calculate

      public static int calculate​(int data, int currentCrc)
      Calculates the CRC X.25-checksum for one byte with regards to the current-checksum.
      Parameters:
      data - byte which should be added to the checksum
      currentCrc - current checksum which should be extended
      Returns:
      checksum composed from a prior checksum and a byte of data

    • calculate

      public static int calculate​(byte[] buffer)
      Calculates the CRC X.25-checksum for a whole byte[] array.
      Must contain the CRC_EXTRA byte which must be added for each message.
      Parameters:
      buffer - of data to calculate a checksum for
      Returns:
      checksum for the whole buffer

    • calculate

      public static int calculate​(byte[] payload, int crc)
      Calculates the CRC X.25-checksum for a given payload array and the right crc-extra extra byte.
      Parameters:
      payload - data to calculate the checksum for
      crc - crc-byte which must be added
      Returns:
      checksum for the payload