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Symmetric Key Cryptography

Symmetric means the same/one key. Consider a scenario where the sender wants to send a message to the receiver then it makes use of a unsecure channel (e.g., internet).

So when the sender is sending this message, it is not sent simply but rather encrypted as C = [K<sub>1</sub>, [M]],

Where M stands for the message, K<sub>1</sub> is the key & C stands for the Cipher Text.

Message M is encrypted with key K<sub>1</sub> and converted into a Cipher Text and this Cipher Text is sent to the receiver. Now receiver will decrypt the Cipher Text and by using the same key for decrypting into the original message.

Methods for Symmetric Key Cryptography

Data Encryption Standard (DES)

It is a 56-bit key. Symmetric Key algorithm uses block-by-block encryption where each block is encrypted individually and later chained together to form the final cipher text. Here the block size is 64 bits and key size is 48 bits and it follows the Feistel Cipher structure.

Triple DES (3DES)

Here a 192-bit key is used.

Advanced Encryption Standard (AES)

AES is a symmetric encryption algorithm, meaning it uses the same key for both encryption and decryption. It is known for it’s speed and efficiency, which makes it suitable for encrypting large amounts of data.

Asymmetric Key Cryptography

Asymmetric Key or Public Key - Here, 2 keys are used Public and Private Key, if we encrypt a message with the public key then it can only decrypted with its corresponding private key. When A wants to send a message to B, he either broadcasts his Public Key in the network or to a trusted third-party person so when B receives the message he can decrypt it.

Now we encounter 4 cases in this:

Encrypting the message with Pub<sub>A</sub>

If we encrypt with Pub<sub>A</sub>, it might create inconvenience as B would require A’s Pri<sub>A</sub> which cannot be shared with anyone.

Encrypting the message with Pub<sub>B</sub>

This is the ideal case since Pri<sub>B</sub> is only available with B and no other node can intercept the communication.

Encrypting the message with Pri<sub>A</sub>

This case is highly flawed, if the message is encrypted with Pri<sub>A</sub> any node in the network can access the message since the Pub<sub>A</sub> was broadcasted everywhere, hence leading to loss of confidentiality.

Encrypting the message with Pri<sub>B</sub>

‘A’ cannot perform this action itself since he’s not aware of B’s Pri<sub>B</sub>.

Rivest-Shamir-Adleman (RSA)

RSA is an asymmetric encryption algorithm that uses a pair of keys, a public key and a private key for decryption. RSA is generally slower and is often used to securely exchange keys rather than for bulk data encryption.