The Call of the Open Sidewalk

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pgpfan:mdc

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pgpfan:mdc [2023/12/11 13:03] – Accuracy. b.walzerpgpfan:mdc [2023/12/11 13:30] (current) – Structure, we have to directly address the 16 bits of security thing b.walzer
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 The situation with the OpenPGP modification detection code (MDC) very much reminds me of the story of the Product. Legend has it that the MDC was created as a kind of an afterthought((Since I first wrote this, I have come to believe that this is //just// a legend. The principles that make the MDC work were known at the time of its design. See the [[pgpfan:intptxt]] article for a related discussion.)). It works very well but it is not obvious why it does. I have never seen an inclusive explanation. Here I will attempt to produce such an explanation. The situation with the OpenPGP modification detection code (MDC) very much reminds me of the story of the Product. Legend has it that the MDC was created as a kind of an afterthought((Since I first wrote this, I have come to believe that this is //just// a legend. The principles that make the MDC work were known at the time of its design. See the [[pgpfan:intptxt]] article for a related discussion.)). It works very well but it is not obvious why it does. I have never seen an inclusive explanation. Here I will attempt to produce such an explanation.
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 +Note that there is a another legend floating around that states that the MDC only has the equivalent of "16 bits of security". This is simply wrong and was probably the result of failing to read to the bottom of an email thread(([[https://mailarchive.ietf.org/arch/msg/openpgp/UYEBC7hnZNbMoNWrfz9zJQb_FUk/|The misread ITEF OpenPGP discussion thread about the security properties of the MDC]])).
  
 When OpenPGP is used for something like email, the messages are authenticated directly with a signature. So the MDC is not relevant in the most common use case. So the MDC is not that important. It would still simplify things and eliminate much pointless discussion if the MDC could in fact be shown as strong. It would eliminate having to go through the more obscure uses of OpenPGP to determine how applicable the MDC was to each. When OpenPGP is used for something like email, the messages are authenticated directly with a signature. So the MDC is not relevant in the most common use case. So the MDC is not that important. It would still simplify things and eliminate much pointless discussion if the MDC could in fact be shown as strong. It would eliminate having to go through the more obscure uses of OpenPGP to determine how applicable the MDC was to each.
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   * [[https://www.rfc-editor.org/rfc/rfc4880#section-5.13|RFC-4880 sec 5.13 (Symmetrically Encrypted Integrity Protected Data packet)]]   * [[https://www.rfc-editor.org/rfc/rfc4880#section-5.13|RFC-4880 sec 5.13 (Symmetrically Encrypted Integrity Protected Data packet)]]
   * [[https://www.rfc-editor.org/rfc/rfc4880#section-5.14|RFC-4880 sec 5.14 (Modification Detection Code packet)]]   * [[https://www.rfc-editor.org/rfc/rfc4880#section-5.14|RFC-4880 sec 5.14 (Modification Detection Code packet)]]
-  * [[https://mailarchive.ietf.org/arch/msg/openpgp/UYEBC7hnZNbMoNWrfz9zJQb_FUk/|IETF OpenPGP email list thread about the security properties of the MDC]] 
-  * [[https://cseweb.ucsd.edu/~mihir/papers/enc-red.pdf|Does encryption with redundancy provide authenticity?]] 
  
 [[pgpfan:index|PGP FAN index]]\\ [[pgpfan:index|PGP FAN index]]\\
 [[em:index|Encrypted Messaging index]] [[em:index|Encrypted Messaging index]]
  
pgpfan/mdc.txt · Last modified: 2023/12/11 13:30 by b.walzer