On Wed, 5 Jul 2006, George Danchev wrote:
> Date: Wed, 05 Jul 2006 19:56:05 +0300
> From: George Danchev <[EMAIL PROTECTED]>
> To: Francisco Rosales <[EMAIL PROTECTED]>
> Cc: Alexander Schmehl <[EMAIL PROTECTED]>, [EMAIL PROTECTED],
> [EMAIL PROTECTED]
> Subject: Re: shc -- #335278 broken packaging -- non-DD NMU prepared
>
>
> Well we start off with 3.7 because it is currently in Debian. The main problem
> is the rc4 implementation which has no copyright attached. That's the reason
> we started replacing it with a clean-room GPL'ed implementation and finally
> make the program licensed free and consistent. Otherwise it will be removed
> from the archive because of legal issues.
>
> For the time being as for 3.7 version with the new GPL'ed rc4 implementation I
> forced intentionally relax/redistributable binary to be created to overpass
> the above 'shell has changed'. I agree, it is far from being perfect.
>
> You can find more information at:
>
> http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=335278
I see.
If the problem is about the copyright of the rc4 implementation,
then you must know the full history.
At some point in 1997 I decided to change from shc-2.7 to 3.0. The
idea was to change totally the way the script is hidden inside the binary.
I decide to use a very beautiful and tiny algorithm I seen published in
the news:
http://groups.google.com/group/comp.lang.c/msg/dce6ba2c5c8dd0d1
As you can see following the previous link, the published
implementation was 4 lines long (283 characters):
---->>>>----
#define S,t=s[i],s[i]=s[j],s[j]=t, /* :usage: rc4 key <file; @RSADSI */
main(int c,char**v){unsigned char*p=*++v,s[256],b[4096],i=0,j=0,t;c=
strlen(p);while(s[i]=i,++i);while(j+=s[i]+p[i%c]S++i);j=0;while(c=read
(0,p=b,4096)){while(c--){j+=s[++i]S*p++^=s[t+=s[i]];}write(1,b,p-b);}}
----<<<<----
...and came with the following invitation:
" Anyone fancy having a go at shrinking this C code? ... "
There was no copyright notice, but obviously there was an explicit
invitation for everybody to take and to modify that code.
I took the invitation, not for shrinking but for improving
readability and usability. The resulting code, which is included in shc.c
file and in any ".x.c" generated file is:
---->>>>----
static unsigned char stte[256], indx, jndx, kndx;
/*
* Reset arc4 stte.
*/
void stte_0(void)
{
indx = jndx = kndx = 0;
do {
stte[indx] = indx;
} while (++indx);
}
/*
* Set key. Can be used more than once.
*/
void key(void * str, int len)
{
unsigned char tmp, * ptr = (unsigned char *)str;
while (len > 0) {
do {
tmp = stte[indx];
kndx += tmp;
kndx += ptr[(int)indx % len];
stte[indx] = stte[kndx];
stte[kndx] = tmp;
} while (++indx);
ptr += 256;
len -= 256;
}
}
/*
* Crypt data.
*/
void arc4(void * str, int len)
{
unsigned char tmp, * ptr = (unsigned char *)str;
while (len > 0) {
indx++;
tmp = stte[indx];
jndx += tmp;
stte[indx] = stte[jndx];
stte[jndx] = tmp;
tmp += stte[indx];
*ptr ^= stte[tmp];
ptr++;
len--;
}
}
----<<<<----
I sincerely think that this code is mostly mine.
Perhaps some i, j, s or p remains from the original, and obviously
I'm not the creator of the rc4 algorithm.
Is almost impossible for "John L. Allen" (wherever he is) to
recognize that code as his code, and obviously his own (beautiful) 4 lines
of code wasn't created from nothing, and he isn't the creator of the rc4
algorithm neither.
So... I sincerely think that this code is mostly mine.
The disclaimer I put on top of shc.c,
---->>>>----
/**
* This software contains the 'Alleged RC4' source code.
* The original source code was published on the Net by a group of cypherpunks.
* I picked up a modified version from the news.
* The copyright notice does not apply to that code.
*/
----<<<<----
...and the header of the rc4 implementation,
---->>>>----
/**
* 'Alleged RC4' Source Code picked up from the news.
* From: [EMAIL PROTECTED] (John L. Allen)
* Newsgroups: comp.lang.c
* Subject: Shrink this C code for fame and fun
* Date: 21 May 1996 10:49:37 -0400
*/
----<<<<----
...were there basically because:
1) In 1997 I was not sure what could happen if I distribute software
using (any implementation of) the rc4 algorithm.
I don't want the NSA of RSA people knock my door.
2) To state that somebody published an implementation before me.
3) To acknowledge that initial implementation.
Today, and being stricter with what I write, both comments could
be rewritten such as something similar to:
/**
* This software contains an ad hoc version of the 'Alleged RC4' algorithm.
* The original source code was published on the Net by a group of cypherpunks.
* A modified version was picked up from the news:
* From: [EMAIL PROTECTED] (John L. Allen)
* Newsgroups: comp.lang.c
* Subject: Shrink this C code for fame and fun
* Date: 21 May 1996 10:49:37 -0400
* The following implementation is a total rewritten based on the previous one.
*/
> > As you have seen, I have implemented the initialization stage with
> > two functions, not one (stte_0 and key). The reason is that I want to be
> > able to apply more than one password, using key fuction several times.
>
> That was what puzzled me a lot in the first place, but seems is the right way
> to go.
>
> > /* 3.8.5 */
>
> I failed to find 3.8.5 version at http://www.datsi.fi.upm.es/~frosal/sources/
> and the rows listed below are not from the last version found 3.8.3.
I've already put it there.
[deleted]
> >
> > As I have already stated, key_with_file (and the ability to use
> > key _incrementally_ several times) permits to make the encryption
> > dependent on some details of a given file. So the decryption of chk2
> > will change if the signature of the given file changes, in other words
> > if the "shell has changed!".
>
> Hm, I'm a little bit confused by the message like "shell has changed", should
> it be more straightforward ... 'signature has changed' or 'decryption
> failed' ?
Well, no in my opinion. These messages could seen more
"straightforward" for us as programmers, but the message is for "the
shc-user" who must know nothing about the implementation, neither
signatures, en/decryptions, etc.
>
> > Perhaps my implementation of arc4 is more add-hoc than yours, but,
> > please, I see no reason to break the described behaviour.
>
> I agree with you. OTOH, in the light of having bits with clear license only we
> should replace the unknown-license cypherpunks code with a license-clear
> implementation.
There is not a single byte of cypherpunk code in shc.c file.
If I have clarified it enough we can keep the actual
implementation as is.
If you finally think that there is no other way that to substitute
that part of the code... then I suggest you to put that code in other file
to be included both from shc.c and from any ".x.c" file. In that way, I'll
keep my own version in a state compatible with yours.
> I'll try to have a look and try to achieve what you describe
> above. The best solution im my opinion will be a new upstream version of shc
> with license-clear arc4 implementation.
>
Thank you for your work.
--
Saludos
Fran
---------------------------------------------------------------------
Francisco Rosales García <[EMAIL PROTECTED]> TEL: +34 91 336 73 80
http://www.datsi.fi.upm.es/~frosal FAX: +34 91 336 73 73
Departamento de Arquitectura y Tecnología de Sistemas Informáticos.
Facultad de Informática. Universidad Politécnica de Madrid. España.
