Security Basics mailing list archives
Re: NewBie:cryptography : DES vs Blowfish?
From: shawn () nunleys com
Date: Sat, 2 Nov 2002 13:47:19 -0800
Which is more secure... that's a broad question, of course. If your intention is to determine the security of the protocol itself, and not the implementation of it in a particular application, then you must look at the various cryptanalysis studies done against each protocol. DES has been proven, time and again, to be very resistant to cryptanalysis attacks, but it does have a limited key size. Most implementations use 56bit keys, and even with triple DES you're only using 2 56bit keys. Blowfish and GOST have not had as much study, but the key sizes can be bigger. So, barring any newly discovered weaknesses (it can happen) you can get more brute-force attack protection from Blowfish and GOST. (plagiarized from aliennetworks.com) DES (Data Encryption Standard) DES is, by far, the worlds most popular encryption solution. DES is a block cipher; it encrypts data in 64-bit blocks. It is also a symmetric algorithm; this implies that it uses the same algorithm and key for decryption and encryption. With a key length of 56 bits, DES performs 16 rounds (Loops) which are comprised of multiple XOR and data substitutions. One of DES strengths is an avalanche effect that is caused by a portion of the result of round 16 being fed back into round one of the next data block; This causes an increase in data diffusion that can make DES very hard to crack. The math behind DES - All possible 64 bit plaintext blocks can be mapped onto all possible 64 bit cipher text blocks in 264! Possible ways. The DES algorithm, with a 56 bit key, will produce around 256 of these mappings (Thats about 100000000000000000 possible mappings). When DES was developed, there was no known way to crack it in a single lifetime; Now, with differential and linear cryptanalysis tools at hand, new advances in computer hardware, and great strides in number theory, a dedicated DES cracking machine could be built for under $1,000,000 that could break any message in just a few hours. In 1984 DES chips capable of performing 256,000 encryptions and decryptions per second were available; in 1987 chips that could do 512,000 were available. In 1993 , Michael Wiener designed a machine that could do a brute-force crack on any DES message, decoding it in 3.5 hours. There are many other attacks that can break DES (Eventually), including differential cryptanalysis, Dif-Lin, meet-in-the-middle, and chosen plaintext. These attacks all share two common factors; theyre very difficult to execute in practice, and they can become expensive. Are their other ways? The algorithm is over 20 years old; the NSA no longer uses it for encrypted transmissions; and the source code and substitution boxes are available in the public domain. The combination of readily available data on the algorithm, exponential increases in computing power, and increasing value of transmitted data is giving many companies a reason to reevaluate DES as their choice for encrypted transmissions. Regrettably, they have few options that offer actual security. Blowfish Blowfish is a fast 64 bit block cipher with a variable-length key. Key expansion in Blowfish can create a 448 bit keyspace quite a bit larger than DES. The major drawback of Blowfish is that it is optimized for applications where the keyspace does not change very often. In spite of this shortcoming, Blowfish passes many security tests, and provides a very good level of security. Blowfish is in the public domain (Anyone can go get the source code for free), and is easy to implement. The math behind Blowfish - Blowfish consists of 16 rounds, or loops. Cryptanalysis of Blowfish by Serge Vaudenay reveals a partial differential attack that can recover the plaintext array in 28r+1 chosen plaintexts. There is also a class of known weak keys that can increase the effectiveness of this attack by a factor of two. [end of plagiarism] In my opinion, it's not the protocol that's the issue nearly as much as the technical implementation and your procedures for protecting your keyspace. Whenever you must resort to using symmetric-key crypto, you face some tough issues with regard to key distribution. -Shawn Quoting DocValde <DocValde () gmx de>:
Hallo Roberto Ramsis, am Freitag, 1. November 2002 um 12:37:15 schrieben Sie:Hello i needed to know,which is more secure : DES , BLOWFISH,GOST? and which is faster? ThanksDES is obsolete since few years, (not only) since its key length is fixed to 56bit effective. Even TripleDES has only 112bit effective. With GOST, i had not to deal yet, but Blowfish seems to be quite good and fast enough for almost any use. Be sure to use 128bit keylength upwards. Best regards, Malte von dem Hagen -- DocValde web: http://www.DocValde.net eMail: DocValde () gmx de icq: 71581747
Current thread:
- NewBie:cryptography : DES vs Blowfish? Roberto Ramsis (Nov 01)
- Re: NewBie:cryptography : DES vs Blowfish? DocValde (Nov 01)
- Re: NewBie:cryptography : DES vs Blowfish? shawn (Nov 04)
- <Possible follow-ups>
- RE: NewBie:cryptography : DES vs Blowfish? Naman Latif (Nov 01)
- Re: NewBie:cryptography : DES vs Blowfish? DocValde (Nov 01)