1 Assuming an initial implementation of your encryption syst

1.) Assuming an initial implementation of your encryption system was done using DES. What issues would need to be addressed if you decide to upgrade to the 3DES algorithm? There are several issues to consider. You should identify at least 4 issues and place them in a numbered list.

While there may be better algorithms than 3DES to upgrade to the problem is not concerned with that. The problem is bounded by the stated parameters of moving from DES to 3DES. There are numerous issues to consider moving from DES to 3DES and these are what you need to focus on.

2.) Your manager is considering purchasing a message authentication system. She is considering 3 different systems. One system uses MD5 hashing, another uses SHA2 hashing and the other system uses a brand new hashing algorithm called VSH (Very Smooth Hash). You have been asked to prepare an executive summary (i.e. clear and concise) that describes the attributes of each algorithm and the pros and cons. You should consider reviewing each algorithm along the same primary dimensions and then focus on differentiating factors where appropriate.

What would your recommendation be and why?

3.) How would you protect the passwords on your system using some of the mechanisms we have studied? Discuss implementation strategies and explain your decisions for the choices you have made.

Solution

Ans 1)

DES or Data encryption standard is a block cipher, encryption algorithm, which encrypts messages of block size 64 bits and produces cryptograms of length 64 bits using a 56-bit key (DES keys are actually 64 bits in length but 8 bits act as parity bits so only 56 bits are
actually used for encryption).

plain text message(64bits) ----> E ---> 56 bit key ----> cryptogram(64bits)

Triple-DES, noted as 3DES from here on, uses 2 keys, chosen independently
at random, to DES encrypt a message multiple times. There are also ways to use
3DES with 3 different keys, but these schemes do not give a significant amount
of extra security in theory and are not considered in financial systems. The most
common technique is to encrypt the initial plaintext message with one key, decrypt
the result with a second key and finally encrypt this last result with the first
key again. This is known as E-D-E double length key 3DES encryption.

Plain text message ----> E(Key 1) ----> D(key 2) -----> E(Key 3) ----->cryptogram

Issues regarding upgrading from DES with 3DES are numerous. You cant simply replace DES with 3DES, security wise and operationally wise.
1) DES is the weakest link
If a single entity in the system still utilizes single DES there is a possibility that the security of the whole system might be compromised by an attack on single DES. Due to the complexity of financial systems, it is not feasible to replace all keys with 3DES keys right away, systems will have to live in a heterogeneous state. It is important however to analyze each situation and to consider how the system satisfies the security properties wanted. Most certainly, until all keys are replaced with 3DES keys, the system will not achieve 2^112 security, but the system can be upgraded progressively so as to withstand more and more attacks. Security, as in this case, is often an incremental process.

2)The algorithm itself
When using 3DES certain variants of modes of operations are available which are
not for single DES. Some of these variants may seem attractive at first glance because
of their performance gain properties, unfortunately they are not all secure.
For example, for single DES, cipher-block chaining (CBC) is a good mode to use
since it is provably secure. However, there are different ways of implementing
CBC mode for 3DES, one can use triple-outer-CBC mode (CBC mode applied directly
to 3DES) or triple-inner-CBC mode (a variant, a multiple encryption mode
of operation where the feedbacks are taken from the single DES operations of
which 3DES is composed of).

3)Updates in hardware
There are obvious problems if hardware, such as PIN pads, ATMs and cryptographic
processors, cannot be upgraded in the field. Even if upgrades can be done
in the field, migration has to be coordinated with other devices and software. If a
PIN pad can only use single DES and a switch has been upgraded to use 3DES,
the switch needs to be configured to be backwards compatible with single DES.
This backwards compatibility feature could potentially be used to the advantage
of an attacker.

4)3DES is much slower than DES
3DES encryption and decryption takes approximately
three times longer to execute than does single DES encryption and decryption.
Memory allocation and caching can also affect the speed of execution
of 3DES encryption and decryption, especially during the key setup stages.

5)Key Management
Split knowledge schemes for 3DES are different than
those for single DES and it is important to make sure that the new schemes that
will be used continue to satisfy the security requirements. When one splits a 3DES
key between two individuals, a typical scheme will produce four parts, K1L and
K2L, which when XORed together forms KL (the first part of the 3DES key) as
well as K1R and K2R which when XORed together forms KR (the other part of
the 3DES key). Now, the scheme is secure if the first person is in custody of K1L
and K1R, and the second person is in custody of K2L and K2R. This way, neither
individual has any information what so ever about the 3DES key. However, if the
first individual is in custody of K1L and K2L, and the second of K1R and K2R,
each individual learns information about the key (notably, one whole part of the
key by XORing both of the individual’s parts together). If one of the individuals
can have access to the encryption of a message under the key in question (most
processors will have a command that will allow them to do so), they simply need
to do the equivalent of a brute force attack on a single DES key to compute the
whole 3DES key. Thus, there is not 2^112 security.