ds.ov2.front
Class Hash_size

java.lang.Object
  ds.ov2.front.Hash_size

public class Hash_size
extends Object

Computes the size of the hash that is used in both Signature and Host_signature. The underlying digest SHA-1 produces always 160 bit hashes. For using smaller RSA keys (for instance in the host test frame or in the Montgomerizing applet) this means that hash does not fit into existing variables. To avoid complications in these cases (where security is irrelevant anyways) I restrict the hash size appropriately. This is done both in Signature and Host_signature by using only some last bytes of the digest. This class computes the hash size. See Signature for a more elaborated discussion of the hash size problem.

CPP Preprocessing

This class uses the following cpp defines: PACKAGE, PUBLIC, ASSERT

Execution Environment:

host, card

Author:

Hendrik Tews

Version:

$Revision: 1.10 $

Last Commit:

$Date: 2010-02-16 10:26:07 $ by $Author: tews $

Field Summary

static short

digest_output_size The output size that the SHA-1 digest produces when used in Signature and Host_signature.

Constructor Summary

protected

Hash_size() Static class, object construction disabled.

Method Summary

static short

hash_size(short short_bignat_size, byte applet_id) Compute the hash size, depending on the size for short (exponent) bignats.

Methods inherited from class java.lang.Object

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

Field Detail

digest_output_size

public static final short digest_output_size

The output size that the SHA-1 digest produces when used in Signature and Host_signature.

See Also:

Constant Field Values

Constructor Detail

Hash_size

protected Hash_size()

Static class, object construction disabled.

Method Detail

hash_size

public static short hash_size(short short_bignat_size,
                              byte applet_id)

Compute the hash size, depending on the size for short (exponent) bignats. Normally the size should not exceed 2 * short_bignat_size -1, but for the Montgomerizing applet it is restricted to short_bignat_size.

Parameters:

short_bignat_size - the size of short (exponent) bignats in bytes

applet_id - the applet ID, see RSA_data.applet_id.

Returns:

size of the hash in bytes