3DES

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Jun 9, 2009 5:01 AM
Jun 9th, 2009

Introduction

Triple DES (3DES)

The Data Encryption Standard (DES) was developed by an IBM team around 1974 and adopted as a national standard in 1977. Triple DES is a minor variation of this standard. It is three times slower than regular DES but can be billions of times more secure if used properly. Triple DES enjoys much wider use than DES because DES is so easy to break with today's rapidly advancing technology.This just serves to illustrate that any organization with moderate resources can break through DES with very little effort these days.

Triple DES was the answer to many of the shortcomings of DES. Since it is based on the DES algorithm, it is very easy to modify existing software to use Triple DES. It also has the advantage of proven reliability and a longer key length that eliminates many of the shortcut attacks that can be used to reduce the amount of time it takes to break DES. However, even this more powerful version of DES may not be strong enough to protect data for very much longer. The DES algorithm itself has become obsolete and is in need of replacement.

The AES is as strong as Triple DES and probably much faster. Many security systems will probably use both Triple DES and AES for at least the next five years. After that, AES may supplant Triple DES as the default algorithm on most systems if it lives up to its expectations. But Triple DES will be kept around for compatibility reasons for many years after that. So the useful lifetime of Triple DES is far from over, even with the AES near completion. For the foreseeable future Triple DES is an excellent and reliable choice for the security needs of highly sensitive information.

In Depth

Triple DES is simply another mode of DES operation. It takes three 64-bit keys, for an overall key length of 192 bits. In Private Encryptor, you simply type in the entire 192-bit (24 character) key rather than entering each of the three keys individually. The Triple DES DLL then breaks the user provided key into three subkeys, padding the keys if necessary so they are each 64 bits long. The procedure for encryption is exactly the same as regular DES, but it is repeated three times. Hence the name Triple DES. The data is encrypted with the first key, decrypted with the second key, and finally encrypted again with the third key.

des3p1.gif

Consequently, Triple DES runs three times slower than standard DES, but is much more secure if used properly. The procedure for decrypting something is the same as the procedure for encryption, except it is executed in reverse. Like DES, data is encrypted and decrypted in 64-bit chunks. Unfortunately, there are some weak keys that one should be aware of: if all three keys, the first and second keys, or the second and third keys are the same, then the encryption procedure is essentially the same as standard DES. This situation is to be avoided because it is the same as using a really slow version of regular DES.

RFC:

  • The ESP Triple DES Transform - RFC 1851
  • The ESP DES-CBC Transform - RFC 1829
  • The ESP DES-CBC Cipher Algorithm With Explicit IV - RFC 2405
  • The PPP DES Encryption Protocol, Version 2 (DESE-bis) - RFC 2419
  • The PPP Triple-DES Encryption Protocol (3DESE) - RFC 2420
  • Security Implications of Using the Data Encryption Standard (DES) - RFC 4772

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Posted June 9, 2009 at 5:01 AM
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