Path: ...!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!eternal-september.org!.POSTED!not-for-mail From: Richard Heathfield Newsgroups: sci.crypt Subject: Re: Seriation Date: Mon, 3 Feb 2025 10:17:24 +0000 Organization: Fix this later Lines: 42 Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Injection-Date: Mon, 03 Feb 2025 11:17:24 +0100 (CET) Injection-Info: dont-email.me; posting-host="a3ec2fab6b8d3856494b525f308faa8d"; logging-data="1275858"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX18MR9VJ/ZWNZgoaLRKhv3bpOmyeiyk5kyC0/xbBir2Wxg==" User-Agent: Mozilla Thunderbird Cancel-Lock: sha1:daw76K+dMUnuSauhQYdN8dOVb6M= In-Reply-To: Content-Language: en-GB Bytes: 3089 On 03/02/2025 09:00, David Entwistle wrote: > On Sun, 2 Feb 2025 10:06:03 -0000 (UTC), David Entwistle wrote: > >> I did have a bit of trouble with SCOS, not because it was hard to >> decrypt, >> but my implementation wasn't... There's a word, but I'm not sure what it >> is... When you perform an operation on a set, the result of that >> operation is should be guaranteed to belong to the same original set, >> but in my case it wasn't. So in this case, when encrypting and >> decrypting occasionally, due to some odd punctuation mark, or an >> accented character, the result would lie outside the reasonable bounds >> of characters. The web, which I often use as a source of plain text, is >> full of such characters. That was my problem, not a problem with SCOS, >> but it did cause me some grief. > > "Closure: In mathematics, a subset of a given set is closed under an > operation of the larger set if performing that operation on members of the > subset always produces a member of that subset". > > So, should an encryption / decryption operation always be closed? Maybe > SCOS was closed, but I think it would depend how you defined the full > character set and that may have to be quite wide. In a sense, SCOS's character set is defined by these four lines: #define UPPER "ABCDEFGHIJKLMNOPQRSTUVWXYZ" #define LOWER "abcdefghijklmnopqrstuvwxyz" #define DIGIT "0123456789" #define PUNCT "!\"$%^&*()_-+={}[]#~'@;:/?.>,<\\|" which isn't particularly wide, but any encryption of any of those characters will *always* produce a character drawn from the same set. When faced with something *not* from that set, SCOS leaves it unchanged. So I think I'm right in saying that by the above definition SCOS /is/ closed. -- Richard Heathfield Email: rjh at cpax dot org dot uk "Usenet is a strange place" - dmr 29 July 1999 Sig line 4 vacant - apply within