DES and 3DES

Data Encryption Standard (DES) data are encrypted in 64-bit blocks using a 56-bit key. The DES algorithm takes the input through a series of transformations: initial permutation; a complex function, which involves both permutation and substitution operations and depends on a key input; a simple permutation function that switches the two halves of the data; the function is applied again; and a permutation function that is the inverse of the initial permutation takes place. There are five “modes of operation” that have been defined in order to apply DES to a variety of applications. They are Electronic Codebook, Cipher Block Chaining, Cipher Feedback, Output Feedback Counter, and Counter (Cryptography Concepts, 2005).

Triple DES or 3DES involves repeating the DES algorithm three times on the plaintext, using two or three different keys to produce the ciphertext. As stated in the article DES is dead. Long live…Well, um, What, “First it encrypts, then it decrypts and finally it encrypts again” (Moskowitz, 1999). Three DES is now used because it is very resistant to cryptanalysis, serving as an alternative to add security against the potential vulnerability of DES to brute-force attack. Triple DES has been adopted for use in the key management standards ANSI X 9.17 and ISO 8732, along with a number of Internet-based applications, such as PGP and S/MIME (AES, Ciphers, and Confidentiality, 2005). The picture below shows the triple encryption process, as well as show the middle portion of 3DES as a decryption rather than an encryption making it more secure.

A nonce and key distribution center (KDC) shares a secret key or “master” key between each party on a network. The KDC is responsible for generating nonce and keys to be used for a short time over a connection between two parties, known as session keys, and for distributing those keys using the master keys to protect the distribution. The following steps occur:

1. A issues request to the KDC for a session key with B. The message includes the identity of A and B, as well as a unique identifier for the transaction, a nonce, which may include a random number or a counter.

2. The KDC replies with a message encrypted using Ka. Thus, only A can read the message and knows the message originated at the KDC. The message includes:

• The one-time session key, Ks, to be used for the session.
• The original request message, including the nonce, to enable A to match this response with the appropriate request.

In addition, the message includes two items intended for B:

• The one-time session key, Ks.
• An identifier of A, IDA.

These are encrypted with the master key that the KDC shares with B. They are sent to B to establish connection and prove A’s identity.

3. A stores the session key for use in the upcoming session and forwards to B the information that originated at the KDC for B. This information is protected from eavesdropping, because it is encrypted by the master key, Kb. B knows the session key, A’s identity, and that the information originated at the KDC.

4. B then sends a nonce, N2, to A, using a newly minted session key for encryption.

5. Using the session key, A responds with f(N2), where f is a function that performs some transformation on N2 (e.g., adding one) (Stallings, 2003 pgs 214-15).

In conclusion, the above explained how DES works, why 3DES is now used, why the middle portion of 3DES is a decryption rather than an encryption, and explain a nonce and a key distribution center.

Works Cited

Moskowitz, Robert. (1999). DES is dead. Long Live… well, um, what? Network Computing, vol. 10 issue 6. Retrieved October 22, 2005, from, EBSCO Host Research Databas

Stallings, William. (2003). Cryptography and Network Security: Principles and Practice. New Jersey: Pearson Education, Inc.
Joshua Maluchnik, M.I.T., MCP/MCTS
Account Executive
Tranztec Solutions, Inc.
http://www.tranztec.com

How to Send a Secret Message

Introduction

The term Steganography as well cryptography was derived from the Greek language. Cryptography is essentially the art of secret writing and the goal is to maintain the secrecy of the message even if it is visible. Steganography, means covered writing, and is a long-practiced form of hiding information. It should not be seen as a replacement for cryptography but rather as a complement to it.

Cryptography is used to conceal the content of a message, while steganography is used to conceal the existence of a message.

The technology behind effective Steganography is quite complex and involves serious mathematical computations. Computers and technology make this an easy task and make this art of deception a serious threat to the security of

information. The strength of a steganographic algorithm depends on its ability to successfully withstand attacks. Companies with important and sensitive information, and relying on the security and integrity of their intellectual property, could be at significant risk.

Steganography under various media

Steganography includes a vast array of techniques for hiding messages in a variety of media. Among these methods are invisible inks, covert channels, digital signatures, microdots, and spread-spectrum communications. New age technology helps steganography to use various mediums like – text, images, sound, signals, and more.

Steganography in Text

This process involves using steganography within text, i.e. documents or emails. This process is used to counteract the wide scale piracy or illegal distribution of documents, wherein infringers make identical copies of documents without paying royalties to the original author.

  1. Line-Shift coding: In this method, text lines are vertically shifted to encode the document uniquely.
  2. Word-Shift coding: In this method, codewords are coded into a document by shifting the horizontal locations of words within text lines, while maintaining a natural spacing appearance.
  3. Feature coding: In feature coding, certain text features are altered, or not altered, depending on the codeword. For example, one could encode bits into text by extending or shortening the vertical end lines of letters such as p, q, y, etc.

Steganography in Images

This process involves exploiting the Human Visual System (HVS). Image steganography is being increasingly used due to the development of powerful graphical computers and the increasing softwares over the internet.

  1. Image Compression: Image compression helps in reducing the file size by compressing it to a certain extent. Two kinds of image compression are lossless and lossy compression.
  2. Image Encoding techniques: This technique involves in hiding the secret information within the image. It can be done in many ways, like encoding every bit of information in the image or encoding only in the noisy areas of the image.

Steganography in Audio

This form of steganography is very sensitive to handle, as it involves exploiting the Human Auditory System (HAS). We call it sensitive, because the HAS posses a large dynamic range but a small differential range. The following are the methods of this type of steganography –

  1. Phase Coding – This process involves substituting the phase of an initial audio segment with a reference phase that represents the data.
  2. Low bit encoding – This process is similar to image encoding, wherein binary data is stored in the audio files.
  3. Spread Spectrum – In this process, the encoded data is spread across the frequency of the audio data.
  4. Echo Data Hiding – Echo data hiding embeds data into a host signal by introducing an echo.

Conclusion

There are so many components to this form of deception, which are increasingly used either for safeguarding some valuable data or for destroying it. The thing with white collar crimes is that criminals don’t necessarily “look” like criminals and they often proceed for years without being caught. This article aims to make people aware of this form of deception and the threat it poses to digital security.

The author is a technology trainer and consultant who helps businesses build their online brand. His key passion apart from writing articles is Web 2.0 technologies and re-creating value for living. If you feel Sameer can be of any help to you, please send an email