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(semi-OT): Correct definition of the DES OFB?
From: Saqib Ali <docbook.xml () gmail com>
Date: Sun, 24 Jul 2005 06:36:39 -0700
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/
Current thread:
- (semi-OT): Correct definition of the DES OFB? Saqib Ali (Jul 24)
- RE: (semi-OT): Correct definition of the DES OFB? Clement Dupuis (Jul 24)
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- Re: (semi-OT): Correct definition of the DES OFB? Saqib Ali (Jul 24)