Package com.dalsemi.onewire.application.sha

Class SHADebitUnsigned

java.lang.Object
com.dalsemi.onewire.application.sha.SHATransaction
com.dalsemi.onewire.application.sha.SHADebitUnsigned
public class SHADebitUnsigned extends SHATransaction

This class implements an account debit application for unsigned SHA Transactions. Account data is stored on user iButtons with no digital signature (unlike SHADebit which signs the data with a coprocessor iButton).

You may be wondering, "Why use a SHA transaction interface for unsigned account data?" The answer is for increasing transaction times with the DS1961S user iButton. All data writes to the DS1961S require knowledge of the iButton's unique secret, which prevents tampering with the account data. Since a data signature on account data is designed for the same purpose, it is removed from this transaction to remove redundancy and achieve better performance with the DS1961S.

Due to the nature of the DS1961S/DS2432 (i.e. it's designed as a battery-less EEPROM device for 'touch' environments), it is possible that account data could be corrupted if the writing of the data is interrupted. In fact, it is also possible that if the writing of a single bit is interrupted, that bit could become borderline (i.e. right on the line of being a 1 or a 0, such that the 1-Wire I/O logic reads it as a 1 and the SHA engine reads it as a 0) and could be permanently corrupted. As a workaround to problems of this nature, a double-write scheme is used where the length indicates which record is the actual account balance.

The account file consists of the following:

  • 1 byte: Length of the account file
  • 1 byte: Account data type (dynamic or static)
  • 2 bytes: Account Money Conversion Factor
  • 4 bytes: Don't Care
  • Record A
  • 3 bytes: Account Balance
  • 2 bytes: Transaction ID
  • 1 byte: File continuation pointer
  • 2 bytes: CRC16 of 14 bytes seeded with the page number
  • Record B
  • 3 bytes: Account Balance
  • 2 bytes: Transaction ID
  • 1 byte: File continuation pointer
  • 2 bytes: CRC16 of 22 bytes seeded with the page number
  • 24 bytes Total

If the length of the account file is 13, then the current record is Record A. If the length of the account file is 21, then the current record is Record B. When updating the button, first the other record is updated (i.e. if Record A is current, then update Record B with the new balance) and write the new data for that record to the button. After verifying that the data was written correctly, the file pointer is the updated to point to the new record. If data corruption occurs at any point in the transaction (and the user doesn't hang around long enough to allow the transaction system a chance to fix it), the next time the user performs a transaction it is possible to discern what the last known good value is.

A typical use case for this class might be as follows: 

 OneWireContainer18 coprOWC18 = new OneWireContainer18(adapter, address);

 // COPR.0 is the filename for coprocessor service data
 SHAiButtonCopr copr = new SHAiButtonCopr(coprOWC18, "COPR.0");

 // Initial amount for new users is $100, and debit amount is 50 cents
 SHATransaction trans = new SHADebitUnsigned(copr, 10000, 50);

 OneWireContainer33 owc33 = new OneWireContainer33(adapter, userAddress);

 // The following constructor erases all transaction data from the user and
 // installs the system authentication secret on the user iButton.
 // The second instance of coprocessor is used for write-authorization. If
 // you're
 // not using the system coprocessor for data signing, it can be re-used for
 // this
 // purpose.
 SHAiButtonUser user = new SHAiButtonUser33(copr, copr, owc33, true, authSecret);

 // creates account data on iButton
 if (trans.setupTransactionData(user))
        System.out.println("Account data installed successfully");
 else
        System.out.println("Account data installation failed");

 // ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ...

 // verifies authentication response of user iButton from "challenge"
 if (trans.verifyUser(user)) {
        System.out.println("User Verified Successfully");

        // Checks to see that account balance is greater than zero
        if (trans.verifyTransactionData(user)) {
                System.out.println("Account Data Verified Successfully");

                // performs the debit and writes the new account balance
                if (trans.executeTransaction(user)) {
                        System.out.println("Account debited.");
                        System.out.println("New Balance: " + trans.getParameter(SHADebit.USER_BALANCE));
                }
        }
 }

 // ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ...

 if (trans.getLastError() != 0) {
        System.err.println("Error code: " + trans.getLastError());
 }

This class makes use of several performance enhancements for TINI. For instance, most methods are synchronized to access instance variable byte arrays rather than creating new byte arrays every time a transaction is performed. This could hurt performance in multi-threaded applications, but the usefulness of having several threads contending to talk to a single iButton is questionable since the methods in com.dalsemi.onewire.adapter.DSPortAdapter beginExclusive(boolean) and endExclusive() should be used.

See Also:

  • Field Details

    • DEBIT_AMOUNT

      public static final int DEBIT_AMOUNT
      Update the amount this transaction will debit
      See Also:

    • INITIAL_AMOUNT

      public static final int INITIAL_AMOUNT
      Update the amount for initial account balance
      See Also:

    • USER_BALANCE

      public static final int USER_BALANCE
      Retrieve the amount for user's current balance
      See Also:

  • Constructor Details

    • SHADebitUnsigned

      protected SHADebitUnsigned()
      User apps should never call this

    • SHADebitUnsigned

      public SHADebitUnsigned(SHAiButtonCopr copr)
      SHADebitUnsigned constructor. copr is the SHAiButtonCopr that is used to perform this transaction. After saving a reference to the SHA coprocessor, this constructor resets all parameters for this type of transaction to their default values.
      Parameters:
      copr - The coprocessor used for authentication and data signing in this transaction.

    • SHADebitUnsigned

      public SHADebitUnsigned(SHAiButtonCopr copr, int initialAmount, int debitAmount)
      SHADebitUnsigned constructor. copr is the SHAiButtonCopr that is used to perform this transaction. After saving a reference to the SHA coprocessor, this constructor resets all parameters for this type of transaction to their default values.
      Parameters:
      copr - The coprocessor used for authentication and data signing in this transaction.

  • Method Details

    • setupTransactionData

      public boolean setupTransactionData(SHAiButtonUser user) throws OneWireException, OneWireIOException

      Setup account data on a fresh user iButton. Prior to calling setup transaction data, the authentication secret for the iButton should already be setup and a directory entry (as well as at least an empty placeholder file) should exist for the account data. If you constructed the SHAiButtonUser using SHAiButtonUser(SHAiButtonCopr,OneWireContainer18,boolean,byte[]) the secret has been setup for you and you should know call this function. If you try to install the authentication secret after creating the account data, you will destroy all account data on the iButton.

      You can set the value of the initial account balance by calling transaction.setParameter(SHADebit.INITIAL_AMOUNT,10000) where the value of the units is in cents (i.e. 10000 = $100).

      Flow of action:

      • Generate generic account page
      • Insert the initial balance into account data
      • Insert the (constant) digital signature
      • Write account data page to iButton

      Specified by:
      setupTransactionData in class SHATransaction
      Parameters:
      user - SHAiButtonUser upon which the transaction occurs.
      Returns:
      trueif and only if the signature is successfully created by the coprocessor AND the data is successfully written to the user iButton.
      Throws:
      OneWireException
      OneWireIOException
      See Also:

    • verifyUser

      public boolean verifyUser(SHAiButtonUser user) throws OneWireException, OneWireIOException

      Verifies user's authentication response. User is "authenticated" if and only if the digital signature generated the user iButton matches the digital signature generated by the coprocessor after the user's unique secret has been recreated on the coprocessor.

      Flow of action:

      • Generate 3-byte "challenge" on coprocessor
      • Write challenge to scratchpad of user
      • Read account data page with signature
      • Attempt to match user's signature with the coprocessor

      Specified by:
      verifyUser in class SHATransaction
      Parameters:
      user - SHAiButtonUser upon which the transaction occurs.
      Throws:
      OneWireException
      OneWireIOException
      See Also:

    • verifyTransactionData

      public boolean verifyTransactionData(SHAiButtonUser user) throws OneWireException, OneWireIOException

      Verifies user's account data. Account data is "verified" if and only if the account balance is greater than zero. No digital signature is checked by this transaction.

      Flow of action:

      • Read the account data from user
      • Extract account balance
      • Debit money from balance
      • Insert the new balance
      • Write the account data to the user

      If previous steps have been executed, all "Read" commands on the user are reading from cached data.

      Specified by:
      verifyTransactionData in class SHATransaction
      Parameters:
      user - SHAiButtonUser upon which the transaction occurs.
      Returns:
      true if and only if the account balance is greater than zero.
      Throws:
      OneWireException
      OneWireIOException
      See Also:

    • executeTransaction

      public boolean executeTransaction(SHAiButtonUser user, boolean verifySuccess) throws OneWireException, OneWireIOException

      Performs the unsigned debit, subtracting the debit amount from the user's balance and storing the new, unsigned account data on the user's iButton. The debit amount can be set using transaction.setParameter(SHADebit.DEBIT_AMOUNT, 50), where the value is in units of cents (i.e. for 1 dollar, use 100).

      Flow of action:

      • Read the account data from user
      • Extract account balance
      • Assert balance greater than debit amount
      • Debit money from balance
      • Insert the new balance
      • Write the account data to the user

      If previous steps have been executed, all "Read" commands on the user are reading from cached data.

      Specified by:
      executeTransaction in class SHATransaction
      Parameters:
      user - SHAiButtonUser upon which the transaction occurs.
      Returns:
      true if and only if the user has enough in the account balance to perform the requested debit AND the account data has been written to the button.
      Throws:
      OneWireException
      OneWireIOException
      See Also:

    • getParameter

      public int getParameter(int type)

      Retrieves the value of a particular parameter for this debit transaction.

      Valid Parameters

      • SHADebit.DEBIT_AMOUNT
      • SHADebit.INITIAL_AMOUNT
      • SHADebit.USER_BALANCE

      Note that the value of SHADebit.USER_BALANCE will be set after calling verifyTransactionData(SHAiButtonUser) and after calling executeTransaction(SHAiButtonUser).

      Specified by:
      getParameter in class SHATransaction
      Returns:
      The value of the requested parameter.
      Throws:
      IllegalArgumentException - if an invalid parameter type is requested.

    • setParameter

      public boolean setParameter(int type, int param)

      Sets the value of a particular parameter for this debit transaction.

      Valid Parameters

      • SHADebit.DEBIT_AMOUNT
      • SHADebit.INITIAL_AMOUNT

      Specified by:
      setParameter in class SHATransaction
      Parameters:
      type - Specifies the parameter type (SHADebit.DEBIT_AMOUNT or SHADebit.INITIAL_AMOUNT)
      Returns:
      true if a valid parameter type was specified and the value of the parameter is positive.
      Throws:
      IllegalArgumentException - if an invalid parameter type is requested.

    • resetParameters

      public void resetParameters()

      Resets all transaction parameters to default values

      Specified by:
      resetParameters in class SHATransaction