Difference Between DES (Data Encryption Standard) and AES (Advanced Encryption Standard)

DES (Data Encryption Standard) and AES (Advanced Encryption Standard) both are the symmetric block cipher. AES was introduced to overcome the drawback of DES. As DES has a smaller key size which makes it less secure to overcome this triple DES was introduced but it turns out to be slower. Hence, later AES was introduced by the National Institute of Standard and Technology.

The basic difference between DES and AES is that in DES plaintext block is divided into two halves before the main algorithm starts whereas, in AES the entire block is processed to obtain the ciphertext.

Let us discuss some more differences between DES and AES with the help of the comparison chart shown below.

Content: DES Vs AES

1. Comparison Chart
2. Definition
3. Key Differences
4. Conclusion

Comparison Chart

Basis for Comparison	DES (Data Encryption Standard)	AES (Advanced Encryption Standard)
Basic	In DES the data block is divided into two halves.	In AES the entire data block is processed as a single matrix.
Principle	DES work on Feistel Cipher structure.	AES works on Substitution and Permutation Principle.
Plaintext	Plaintext is of 64 bits	Plaintext can be of 128,192, or 256 bits
Key size	DES in comparison to AES has smaller key size.	AES has larger key size as compared to DES.
Rounds	16 rounds	10 rounds for 128-bit algo 12 rounds for 192-bit algo 14 rounds for 256-bit algo
Rounds Names	Expansion Permutation, Xor, S-box, P-box, Xor and Swap.	Subbytes, Shiftrows, Mix columns, Addroundkeys.
Security	DES has a smaller key which is less secure.	AES has large secret key comparatively hence, more secure.
Speed	DES is comparatively slower.	AES is faster.

Definition of DES (Data Encryption Standard)

Data Encryption Standard (DES) is a symmetric key block cipher that was adopted by National Institute of Standard and Technology in the year 1977. DES is based on the Feistel structure where the plaintext is divided into two halves. DES takes input as 64-bit plain text and 56-bit key to produce 64-bit Ciphertext.

In the figure below you can see the encryption of plaintext using DES. Initially, the 64-bit plaintext undergoes initial permutation which rearranges the bits to get 64-bit permuted input. Now this 64 bit permuted input is divided into two halves i.e. 32-bit left portion and 32-bit right portion. Both this portion undergoes sixteen rounds where each round follows the same functions. After completion of sixteen rounds, final permutation is done, and the 64-bit ciphertext is obtained. Each round contains following functions:

• Expansion Permutation: Here the 32-bit right portion is expanded to form 48-bit right portion.
• Xor: The 48-bit right portion is Xor with 48-bit subkey obtained from the 56-bit key, which results in the 48-bit output.
• S-box: The 48-bit output obtained by Xor step is reduced to 32 bit again.
• P-box: Here the 32-bit result obtained from S-box is again permuted, which result in 32-bit permuted output.

Definition of AES (Advanced Encryption Standard)

Advanced Encryption Standard (AES) is also a symmetric key block cipher. AES was published in 2001 by the National Institute of Standards and Technology. AES was introduced to replace DES as DES uses very small cipher key and the algorithm was quite slower.

AES algorithm takes 128-bit plaintext and 128-bit secret key which together forms a 128-bit block which is depicted as 4 X 4 square matrix. This 4 X 4 square matrix undergoes an initial transformation. This step is followed by the 10 rounds. Among which 9 round contain following stages:

• Subbytes: It uses S-box by which it performs byte by byte substitution of the entire block (matrix). 
• Shift Rows: Rows of the matrix are shifted.
  
• Mix Columns: Columns are of the matrix are shuffled from right to left.
• Add round keys: Here, the Xor of the current block and the expanded key is performed. 
  

And the last 10th round involves Subbytes, Shift Rows, and Add round keys stages only and provides 16 bytes (128-bit) ciphertext.

Conclusion

DES is the older algorithm and AES is the advanced algorithm which is faster and more secure than DES.