Message confidentiality, Encrypt/Decrypt an arbitrary message using secret key cryptography including Base64 encoding.

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 Assignment of Network Security

(NETSEC/IV2020)

Dated: 20 December, 2009


Report topic: Message confidentiality, Encrypt/Decrypt an arbitrary message using secret key cryptography including Base64 encoding.

Introduction

Secret key cryptography is also known as Symmetric Encryption. Here same key is used for both the Encryption and Decryption processes [1]. In this approach, sender and receiver both should know the algorithm to use and the secret key. Sender and receiver should be kept the key secret and they should obtain the key in a secured way [2]. Most commonly used secret key cryptography algorithms are DES, 3DES, RC4 etc [1]. In this test DES has been used to encrypt/decrypt an arbitrary message.

Here Base64 encoding has also been used to encode the message. We know that, while sending SMTP e-mails with attachments normal text files can be attached in plain text format, but binary files (such as image files) cannot be attached in the same way. Binary files need some sort of encoding process to be attached with STMP mail. And the most widely used encoding is Base64 [3].

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Description of DES algorithm

DES Encryption Process

“DES has a very strong internal structure” [2]. The following figure presents an overview of the DES encryption process.

Figure 1: DES Encryption process

In DES encryption process 2 inputs are provided to the encryption function: a 64 bit plain text and a 56 bit secret key. At first, the 64-bit plaintext is initially permuted. In the next step combination of a permutation and substitution function is executed 16 times, it makes 16 rounds. Left half and right half of the output from the last round are swapped and permuted again. ...

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