• java.lang.Object
  
  • javacard.security.MessageDigest
    

public abstract class InitializedMessageDigestextends MessageDigest

The InitializedMessageDigest class is a subclass of the base class MessageDigest. This class is used to generate a hash representing a specified message but with the additional capability to initialize the starting hash value corresponding to a previously hashed part of the message. Implementations of InitializedMessageDigest algorithms must extend this class and implement all the abstract methods.

A tear or card reset event resets a 

InitializedMessageDigest object to the initial state (state upon construction).

Even if a transaction is in progress, update of intermediate result state in the implementation

instance shall not participate in the transaction.

Since:

2.2.2 

protected InitializedMessageDigest()

protected constructor

public abstract void setInitialDigest(byte[] initialDigestBuf, short initialDigestOffset, short initialDigestLength, byte[] digestedMsgLenBuf, short digestedMsgLenOffset, short digestedMsgLenLength) throws CryptoException

This method initializes the starting hash value in place of the default value used by the MessageDigest superclass. The starting hash value represents the previously computed hash (using the same algorithm) of the first part of the message. The remaining bytes of the message must be presented to this InitializedMessageDigest object via the update and doFinal methods to generate the final message digest. Note:

• The maximum allowed value of the byte length of the first part of the message is algorithm specific

Parameters:initialDigestBuf - input buffer containing the starting hash value representing the previously computed hash (using the same algorithm) of first part of the message

initialDigestOffset - offset into initialDigestBuf array where initial digest value data begins

initialDigestLength - the length of data in initialDigestBuf array.

digestedMsgLenBuf - the byte array containing the number of bytes in the first part of the message that has previously been hashed to obtain the specified initial digest value value

digestedMsgLenOffset - the offset within digestedMsgLenBuf where the digested length begins(the bytes starting at this offset for digestedMsgLenLength bytes are concatenated to form the actual digested message length value)

digestedMsgLenLength - byte length of the digested length

Throws: CryptoException - with the following reason codes:

• CryptoException.ILLEGAL_VALUE if the parameterinitialDigestLength is not equal to the length of messagedigest of the algorithm (see LENGTH_* constants LENGTH_SHA ) orif the number of bytes in the first part of the message that has previouslybeen hashed is 0 or not a multiple of the algorithm's block size or greater than the maximum length supported by the algorithm(see ALG_* algorithm descriptions ALG_SHA ).