What are the Weaknesses of Data Encryption Standard?

Weaknesses in Cipher Design − Some weaknesses that have been discovered in the design of cipher are as follows −

  • S-boxes − There are three weaknesses have been discovered in S-boxes which are as follows −

    • In S-box 4, the last three output bits can be changed in the same method as the first output bit by integrating some of the input bits.

    • Two particularly chosen inputs to an S-box array can generate the same output.

    • It is possible to acquire the same output in an individual round by converting bits in only three neighboring S-boxes.

  • D-boxes − One mystery and one weakness were discovered in the design of Dboxes −

    • The goals of the initial and final permutations is not clear.

    • In the expansion permutation (inside the function), the first and fourth bits of every 4-bit series are done again.

Weakness in the Cipher Key − Several weaknesses have been discovered in the cipher key.

Key Size − Critics understand that the most serious weakness of DES is in its key size (56 bits). It can do a brute-force attack on a given ciphertext block, the adversary required to test 256 keys.

  • With available technology, it is applicable to check one million keys per second. This define that it is required higher than 100 years to do brute-force attacks on DES utilizing only a computer with one processor.

  • If it can create a computer with one million chips (parallel processing), therefore it can check the whole key domain in approximately 20 hours.

  • When DES was introduced, the rate of such a computer was over various million dollars, but the cost has dropped quickly. A specific computer was developed in 1998 that discovered the key in 112 hours.

  • Computer networks can pretend parallel processing. In 1977 a set of department used 3500 computers connected to the web to discover a key debated by RSA workshop in 120 days. The key domain was divided between all of these computers, and each computer was responsible to test the element of the domain.

  • If 3500 wired computers can discovered the key in 120 days, a hidden association with 42,000 members can discover the key in 10 days.

Weak Keys − There are four out of 256 possible keys are known as weak keys. A weak key is the one that, after parity drop operation includes either of all 0s, all 1s, or half 0s and half 1s. The round keys produced from some weak keys are the same and have the similar pattern as the cipher key.

For instance, the sixteen round keys generated from the first key is all create of 0s; the one from the second is create of half 0s and half 1s. The reason is that the keygeneration algorithm first break the cipher key into two halves. Shifting or permutation of a block does not modify the block if it is create of all 0s or all 1s.