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/*
* Copyright 2014 Licel LLC.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package javacard.security;
/**
*
* 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
*/
public abstract class InitializedMessageDigest extends MessageDigest {
/**
* protected constructor
*
*/
protected InitializedMessageDigest() {
}
/**
* 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
*
*
*
* @param initialDigestBuf input buffer containing the starting hash value representing the previously
* computed hash (using the same algorithm) of first part of the message
* @param initialDigestOffset offset into initialDigestBuf array where initial digest value data begins
* @param initialDigestLength the length of data in initialDigestBuf array.
* @param 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
* @param 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)
* @param digestedMsgLenLength byte length of the digested length
* @throws CryptoException with the following reason codes: CryptoException.ILLEGAL_VALUE
* if the parameter initialDigestLength is not equal to the length of message digest of the algorithm
* (see LENGTH_* constants {@link MessageDigest#LENGTH_SHA}) or if the number of bytes in the first part of the message that
* has previously been 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 {@link MessageDigest#ALG_SHA}).
*/
public abstract void setInitialDigest(byte[] initialDigestBuf, short initialDigestOffset,
short initialDigestLength, byte[] digestedMsgLenBuf, short digestedMsgLenOffset,
short digestedMsgLenLength) throws CryptoException;
}