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AES 128 vs AES 256 | Difference between AES-128 and AES-256

This page compares AES 128 vs AES 256 and mentions difference between AES-128 and AES-256 encryption techniques. It also mentions benefits and drawbacks of these encryption types.

Introduction: Due to fast development of cloud based data applications, it has become essential to protect data during transmission. Various cryptography algorithms have been developed to ensure confidentiality, data protection, communication, authorization and non-repudiation. Cryptography techniques use mathematics and are used to transform data into secret data which only authorized users can read. There are two groups viz. symmetric and asymmetric cryptography.

Symmetric cryptography uses same key to encrypt and decrypt the message. The algorithms fall under this category include Blowfish, DES, 3DES, AES, CAS, RC6, TEA, IDEA, Serpent, Twofish etc.

Asymmetric cryptography uses two keys viz. one key for encryption as public key and one key for decryption as private key. The algorithms fall under this category include DH, SSH, RSA and SSL.

What is AES ?

AES is block cipher technique in which encryption is done group wise at a time. It uses same key in encryption and decryption process and hence it is called symmetric cryptography.

AES modes

There are two modes in which AES can be implemented viz. Counter mode and Output feedback mode. Operations performed by both the algorithms are depicted in the figure above.

Following are the benefits of AES encryption.
• Most robust security protocol due to its implementation in hardware and software.
• All the blocks follow similar encryption procedure.
• It is stronger and faster compare to Triple-DES algorithm.
• It uses encryption keys of longer size (128 bits or 192 bits or 256 bits). Hence it is difficult to break.

Following are the drawbacks of AES encryption.
• Algorithm has simple algebraic structure but it is complex to implement in software.
• AES in counter mode is very challenging to implement in software with respect to performance and security.

AES-128 Encryption and AES-256 Encryption

Both of these techniques follow same process as below except size of the keys. AES-128 uses 128 bit key size where as AES-256 uses 256 bit key size. There are 10 rounds in AES-128 where as 14 rounds in AES-256 encryption process.
Encryption process consists of different rounds as per key size and each round follows steps outlined below for both AES 128 and 256 encryption techniques.

AES-128 vs AES-256

The decryption process for each round follows following four steps.
➨Inverse ShiftRows
➨Inverse substitute bytes
➨AddRoundKey key
➨Inverse mix columns

Difference between AES-128 and AES-256

Following table mentions comparison between AES-128 and AES-256 encryption techniques with respect to various parameters.

Parameters AES-128 AES-256
• Key Length (Nk words) 4 (i.e. 128 bits) 8 (i.e. 256 bits)
• Block Size (Nb words) or input plain text blocks 4 (i.e. 128 bits) 4 (i.e. 128 bits)
• Number of rounds (Nr) 10 14
• Matrix Block 4 x 4 4 x 8
• Attempts required to break 2128 2256, higher than AES-128
• Level of security Considered secured Much stronger
• Processing power Less than AES-256 More than AES-128
• Execution time or latency Less More

Also refer advantages and disadvantages of AES encryption >> and AES MATLAB Code >>.

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