Help with RC5 algorithm

RC5

[remainder deleted for legal reasons ]

Answer 1

[Walter Roberson]

Under international law, encryption is legally considered a weapon of war, and so is restricted.

Different countries have different laws about what parts of encryption can be publicly discussed, and by who.

Mathworks is primarily a US company and so must follow US laws as to which discussions of encryption it permits.

US laws do not actually prohibit public discussion of encryption. However, the discussion is legally permitted only under one of two circumstances:

• You obtain advance permission from the government of the United States for the discussion — and they might make demands that are difficult for Mathworks to guarantee, such as requiring that the discussion not be available to any citizen of several different countries (no matter in the world where the citizen is); Or
• the discussion must be confined to technology that cannot "easily" be extended beyond a particular keyspace limit.

The "easily extended" part in turn is considered to have two branches:

• it can be a discussion of details of an existing published encryption program that is so complex that relatively few people would be able to increase its keyspace. For example you might discuss ways in which to copy bytes faster in a complicated program
• it can be discussion of encryption theory for an algorithm that for theory reasons cannot work with larger keyspace than the existing legal limit. Unfortunately, the only known algorithm that this is true for, is the "null" encryption algorithm that leaves data completely unchanged. For example the very simple single-letter substitution system can, without technical difficulty, be extended to a very strong encryption.

For these reasons, we cannot permit you to ask your questions on this site.

We understand that this is part of your PhD, and that this is frustrating, but this is law with regard what is considered a literal weapon. We have no choice but obey the law.

The laws about discussion of encryption are different in most of Europe, so you can potentially find other online resources that do permit the discussion: the facilities based in the United States are limited.

[Muhammad Abdulrazek]

I understand your decision mr roperson Sorry i didnt know it is not permitted

[Walter Roberson]

Laws on discussing encryption can be strange. Here in Canada, the law at least used to be that I could discuss any encryption method (unless restricted by contract), but that I could only discuss them with people who were physically present in Canada. I was not required to establish that the person was not on the banned country or banned person list: if they were physically present in Canada then I could assume that the government would have prevented banned people from entering the country and the rest was up my free speech rights.

In practice, since people can fake their locations, I would have to require that they were in my physical presence or the presence of people who I know very well. So these days I do not talk about encryption.