Good day,
The best reference for any of the DES Modes of operation is FIPS81 at:
http://www.columbia.edu/~ariel/ssleay/fip81/fip81.html
You cannot go wrong and it is well explained with illustrations.
If you wish to get more details and targeted responses, you could post your
questions to CISSP specific mailing list such as the CISSPStudy mailing list
at www.cccure.org
Visit http://cccure.org/mailman/listinfo/cisspstudy_cccure.org to subscribe.
Take care
Clement
Clément Dupuis, CD
President/Security Evangelist/Chief Learning Officer (CLO)
CCCure Enterprise Security & Training Inc.
CISSP, GCFW, GCIA, Security+, CEH, CCSA, MBNS, MBIS, MBHS, CCSE, ACE
Tel: 954 364 8410 (Florida)
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The Professional Security Testers Warehouse
http://www.professionalsecuritytesters.org
-----Original Message-----
From: Saqib Ali [mailto:docbook.xml@gmail.com]
Sent: Sunday, July 24, 2005 9:37 AM
To: webappsec@securityfocus.com; security-basics@securityfocus.com!
Subject: (semi-OT): Correct definition of the DES OFB?
Hello All,
I was reading the CISSP Exam Guide by Shon Harris (2nd Edition). She
gives the following definition for DES in the OFB (Output Feedback)
Mode.
"...if DES is working in Output Feedback (OFB) Mode, it is functioning
like a stream cipher by generating a stream of random binary bits to
be combined with the plaintext to create ciphertext. The ciphertext
is fed back to the algorithm to form a portion of the next input to
encrypt the next stream of bits." (page 486)
I thin, the last sentence "The ciphertext is fed back to the algorithm
to form a portion of the next input to encrypt the next stream of
bits" is incorrect. That is what happen in the Cipher Feeback (CFB)
Mode, and NOT theOFB mode.
In OFB mode, the "random value" is fed back into the algorithm. i.e.
the "Random Value" from the previous operation becomes the IV for the
next operation.
Am I correct? Can anyone please validate this? Thanks.
--
In Peace,
Saqib Ali
http://www.xml-dev.com/blog/
