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CHATX - a thread starter that's not as easy as it looks.

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  CHATX - a thread starter that's not as easy as it looks. Richard Heathfield <rjh@cpax.org.uk> - 2021-09-20 10:17 +0100
    Re: CHATX - a thread starter that's not as easy as it looks. MM <mrvmurray@gmail.com> - 2021-09-20 07:00 -0700
      Re: CHATX - a thread starter that's not as easy as it looks. Richard Heathfield <rjh@cpax.org.uk> - 2021-09-20 15:17 +0100
        Re: CHATX - a thread starter that's not as easy as it looks. MM <mrvmurray@gmail.com> - 2021-09-20 10:52 -0700
          Re: CHATX - a thread starter that's not as easy as it looks. Richard Heathfield <rjh@cpax.org.uk> - 2021-09-20 19:10 +0100
    Re: CHATX - a thread starter that's not as easy as it looks. Max <maxturv26@gmx.net> - 2021-09-20 20:36 +0200
      Re: CHATX - a thread starter that's not as easy as it looks. Richard Heathfield <rjh@cpax.org.uk> - 2021-09-20 19:42 +0100
        Re: CHATX - a thread starter that's not as easy as it looks. Max <maxturv26@gmx.net> - 2021-09-20 20:50 +0200
          Re: CHATX - a thread starter that's not as easy as it looks. Richard Heathfield <rjh@cpax.org.uk> - 2021-09-20 21:02 +0100
            Re: CHATX - a thread starter that's not as easy as it looks. Max <maxturv26@gmx.net> - 2021-09-20 22:24 +0200
              Re: CHATX - a thread starter that's not as easy as it looks. Richard Heathfield <rjh@cpax.org.uk> - 2021-09-20 22:08 +0100
        Re: CHATX - a thread starter that's not as easy as it looks. wizzofozz <oxxxxxxxxxxxs@gmail.com> - 2021-09-20 21:43 +0200
          Re: CHATX - a thread starter that's not as easy as it looks. Max <maxturv26@gmx.net> - 2021-09-20 21:50 +0200
        Re: CHATX - a thread starter that's not as easy as it looks. Phil Carmody <pc+usenet@asdf.org> - 2021-09-21 17:00 +0300
          Re: CHATX - a thread starter that's not as easy as it looks. Richard Heathfield <rjh@cpax.org.uk> - 2021-09-21 15:22 +0100
          Re: CHATX - a thread starter that's not as easy as it looks. Max <maxturv26@gmx.net> - 2021-09-21 23:31 +0200
            Re: CHATX - a thread starter that's not as easy as it looks. Richard Heathfield <rjh@cpax.org.uk> - 2021-09-21 23:03 +0100
              Re: CHATX - a thread starter that's not as easy as it looks. Max <maxturv26@gmx.net> - 2021-09-22 00:22 +0200
          Re: CHATX - a thread starter that's not as easy as it looks. wizzofozz <oxxxxxxxxxxxs@gmail.com> - 2021-09-25 13:29 +0200
            Re: CHATX - a thread starter that's not as easy as it looks. Phil Carmody <pc+usenet@asdf.org> - 2021-09-26 14:39 +0300
    Re: CHATX - a thread starter that's not as easy as it looks. Richard Harnden <richard.nospam@gmail.com> - 2021-09-21 15:07 +0100
      Re: CHATX - a thread starter that's not as easy as it looks. Richard Heathfield <rjh@cpax.org.uk> - 2021-09-21 15:18 +0100
        Re: CHATX - a thread starter that's not as easy as it looks. Phil Carmody <pc+usenet@asdf.org> - 2021-09-21 21:43 +0300
          Re: CHATX - a thread starter that's not as easy as it looks. Richard Heathfield <rjh@cpax.org.uk> - 2021-09-21 20:41 +0100
    Re: CHATX - a thread starter that's not as easy as it looks. wizzofozz <oxxxxxxxxxxxs@gmail.com> - 2021-09-25 02:24 +0200
      Re: CHATX - a thread starter that's not as easy as it looks. Richard Heathfield <rjh@cpax.org.uk> - 2021-09-25 05:24 +0100
    Re: CHATX - a thread starter that's not as easy as it looks. Richard Harnden <richard.nospam@gmail.com> - 2021-09-25 13:56 +0100
      Re: CHATX - a thread starter that's not as easy as it looks. Richard Heathfield <rjh@cpax.org.uk> - 2021-09-25 14:21 +0100
        Re: CHATX - a thread starter that's not as easy as it looks. Richard Heathfield <rjh@cpax.org.uk> - 2021-09-25 14:28 +0100
      Re: CHATX - a thread starter that's not as easy as it looks. wizzofozz <oxxxxxxxxxxxs@gmail.com> - 2021-09-25 16:11 +0200

Page 2 of 2 — ← Prev page 1 [2]

#50072

On 20/09/2021 10:17, Richard Heathfield wrote:
> lFcrdtwo,econ you itelt nx
> ook ohns  af you sdinliofy
> ttie aegtrxtxmxuxex xoxexcxyt
> hhs tlxo?ixhx xsxdxtx xnxrxpx
> tFar eat apcrexim,tc t semr poexx
> hot cxnra prodita eua doceyctdion
> a-t sa.dxrxtxax xtxlxoxsx xsxIxcn
> t-ehtrxex xhxnxix xoxkx,xax x xax
> eAed danptns yenetxig
> vnr hop'e sah ro.hxnx
> 

pTseiplo lomtil  hht ii fsr'nxex
ohs brebte  eslttae dtfienetcxxx
abdtxesnaxdsdabdcduae wa dend,elck  xhxsx:xxxx
ne w-e  d-e  deea ss pednieg  aihextxexex xxxx
xpxix xfxlxnxsxtx xextxexsxmx xexgxh
xaxrxox xixex xoxbx xhx xaxexlxnxtx.

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#50074

On 21/09/2021 15:07, Richard Harnden wrote:
> On 20/09/2021 10:17, Richard Heathfield wrote:
>> lFcrdtwo,econ you itelt nx
>> ook ohns  af you sdinliofy
>> ttie aegtrxtxmxuxex xoxexcxyt
>> hhs tlxo?ixhx xsxdxtx xnxrxpx
>> tFar eat apcrexim,tc t semr poexx
>> hot cxnra prodita eua doceyctdion
>> a-t sa.dxrxtxax xtxlxoxsx xsxIxcn
>> t-ehtrxex xhxnxix xoxkx,xax x xax
>> eAed danptns yenetxig
>> vnr hop'e sah ro.hxnx
>>
> 
> pTseiplo lomtil  hht ii fsr'nxex
> ohs brebte  eslttae dtfienetcxxx
> abdtxesnaxdsdabdcduae wa dend,elck  xhxsx:xxxx
> ne w-e  d-e  deea ss pednieg  aihextxexex xxxx
> xpxix xfxlxnxsxtx xextxexsxmx xexgxh
> xaxrxox xixex xoxbx xhx xaxexlxnxtx.
> 

That's certainly one of the problems, yes. Another is that I rushed the 
whole cryptosystem through from conception through software 
implementation to publication for competitive peer review in about 
twelve minutes all told. So I cannot guarantee that other problems may 
not also become apparent. (I can reveal, for example, that my decryption 
code does a workmanlike but less than stellar job and isn't about to win 
any prizes.)

I can report one important theoretical discovery about the system: it 
turns out *not* to be informational-theoretically secure. Who'd ha' 
thunk it, eh?

-- 
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

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#50076

Richard Heathfield <rjh@cpax.org.uk> writes:
> I can report one important theoretical discovery about the system: it
> turns out *not* to be informational-theoretically secure. Who'd ha'
> thunk it, eh?

It's also remarkably readable, once you know what you're doing.

Phil
-- 
We are no longer hunters and nomads. No longer awed and frightened, as we have
gained some understanding of the world in which we live. As such, we can cast
aside childish remnants from the dawn of our civilization.
-- NotSanguine on SoylentNews, after Eugen Weber in /The Western Tradition/

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#50077

On 21/09/2021 19:43, Phil Carmody wrote:
> Richard Heathfield <rjh@cpax.org.uk> writes:
>> I can report one important theoretical discovery about the system: it
>> turns out *not* to be informational-theoretically secure. Who'd ha'
>> thunk it, eh?
> 
> It's also remarkably readable, once you know what you're doing.

Yes, I was surprised by that too; it was then that I suggested to MM 
that it might be crackable by eye. A pencil and paper cipher, really, of 
the "secure vs your kid sister" variety. (I am of course referring to 
Schneier's opening to Applied Cryptography.)

-- 
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

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#50109

Op 20-9-2021 om 11:17 schreef Richard Heathfield:
> lFcrdtwo,econ you itelt nx
> ook ohns  af you sdinliofy
> ttie aegtrxtxmxuxex xoxexcxyt
> hhs tlxo?ixhx xsxdxtx xnxrxpx
> tFar eat apcrexim,tc t semr poexx
> hot cxnra prodita eua doceyctdion
> a-t sa.dxrxtxax xtxlxoxsx xsxIxcn
> t-ehtrxex xhxnxix xoxkx,xax x xax
> eAed danptns yenetxig
> vnr hop'e sah ro.hxnx
> 

Here's my contribution (finally). I resisted the urge to look at the 
spoilers, but the hint from Richard to MM (about the word "encrypt") did 
help.
I had to add some spaces at the end of some lines below to make them 
equal length (copy/paste thingy). I also may have made some off-by-one 
error somewhere in the decryption.

yI mua b tilatl  oot etpxr
,'b t Iif naleytg thi .axt
yIlpooiigeaI dhd 'p iheas
   orkmns  t tienstoclert,b
taRtcoagd   iate to  dMid dh
  lihhurhsIhhnvs foraMm titxa
.hxl
xexp
mT  rape tni ge riph  u cnilnd.d
yocmykt ahdndscrygttfInitcousex
mBnt  na eranf lonsmd us.axg
eothatdkp i tite ateoat xrxu
  Ihmtnstwsyrt eoe atehtnalysie physltnxs.s
t'a 'o  hu ehhrw ir na dne  nmtti  ieet xo
tIa betrwpisdRtcoagd. xe
  t dic yetr  ihhurhsxtxx
lIn llnotp,do hirei eoma mnlripli nfx4
iteaesg ha stlenwsst  y euctypteoox x
amlt.ox
ieshxdxf
rbps.6y
yatep4xc
oIeE1dcNVLKJNbc95ecRdbW4FaK15bZJFIbNlc
KyDvvXGyu2Hp5iywhXmo22zKdWSwy3W0kHG5uw
5ZcMRKaoAZJ9xIJwkaI4AeIoxIdAAIIBxIb0hb
yX3oyQXKom1yuGygKWCggDGKwCCg9HG0lDigwC
AdIkBIdAAIPlAIexIdKAQIbQBIJ0QMCoAIIAAI
gCCKwCCgrGSmiGCwqCDltDHg0TTgpDiKgCCggC
BILAIbaB0Ic0RbaV0KZB9KIooIaA4Yc1FcZRUb
0CzgrHl0rDHgbGlugHm0yQGggCWggjmbuH2boH
tbXBBLbIIXaoBIbABcYJ5bZQhIZI4aY9kbIhlY
pHS0mz3pgQSgpCigyHWpnnSgsiWuomippiGbml
9IbkhJYAtIX0BIbBIKaoBIbABcYJ5bZQhIZI4a
pGigbSlypDS9mD3dgQSgpCigyHWpnnSgsiWuom
IYFkKIolIIAkIJoACI=0
DidpQGKmCGggASKygD=9
rbps.6y xe
yatep4xdxc
MICEgdbNBLbJhbe9MeYRJbd4sCXlkcc9VdZBxe
Kynv9X3yl2ipziXwuXXon2lKxmStuGmyhCGzpX
4bYVkKIk0CbRVZKBIKOEoYIkACIAAIIBBZaB5Z
omSzgCTKgmGluiGtpGgsgiC6giCggCHpyiWs0W
YIbJEYMQ0CMAoIIBAYIAAIIxBbKh0KIoIIIAAa
gCGilWji9iDgKCCsgSC9gGClhizhiQCgKCCggW
AIIABIPBEKI0AIIIBIPAIICAAIIBBYaAlPZABC
gCCgpCTiKzCigCHK0CSgiCiggCCs3SGrsSSxpi
xIXwAbIEJMaoVIYA0ICAAIIBAdIAAPaAAYPtAJ
hDSgrGGqbjSKsCVgpCiggCCwgCCrgSSorVSpyW
dCKAxIbBhZKR8cK4ocIQACIZBcaB5IIl0IeJtb
liGglCiy4XS1ymTgKHCKgmHvyiWs0GGuoHFhsm
bKsJXL5JcdRJacAgJXx4JKkxCWoI
CjxdSnyz3HypXCon1GunySp4gzKq
zO
xz

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#50110

On 25/09/2021 01:24, wizzofozz wrote:
> Here's my contribution (finally). I resisted the urge to look at the 
> spoilers, but the hint from Richard to MM (about the word "encrypt") did 
> help.
> I had to add some spaces at the end of some lines below to make them 
> equal length (copy/paste thingy). I also may have made some off-by-one 
> error somewhere in the decryption.


I got the gist of your enciphered message, but I think I should confess 
(as I've already hinted upthread) that my decipher code didn't do a 
stellar job, cobbled together as it was in a few minutes, so I'm not 
surprised that others, too, have struggled a bit with decryption. I 
suspect I went from Grand Concept to Code Central far too quickly 
without lingering long enough in Thought Parkway.

Congratulations, therefore are certainly due to yourself and others who 
managed to bolt a few missing wheels onto my train.

CHAL2 is very different. I have tested encryption and decryption 
thoroughly, and have even gone to the trouble of doing the bitmap header 
thing to make encrypted bitmaps viewable, and it works both ways (bmp -> 
encrypted viewable bitmap -> decrypted original file).

So the second challenge is fair.

No takers so far, so you're not too late!

-- 
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

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#50120

On 20/09/2021 10:17, Richard Heathfield wrote:
> lFcrdtwo,econ you itelt nx
> ook ohns  af you sdinliofy
> ttie aegtrxtxmxuxex xoxexcxyt
> hhs tlxo?ixhx xsxdxtx xnxrxpx
> tFar eat apcrexim,tc t semr poexx
> hot cxnra prodita eua doceyctdion
> a-t sa.dxrxtxax xtxlxoxsx xsxIxcn
> t-ehtrxex xhxnxix xoxkx,xax x xax
> eAed danptns yenetxig
> vnr hop'e sah ro.hxnx
> 

Here's my chatx encoder/decoder effort.
I spent far too much time on this.


#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define MAX_LINE 1024

typedef void (*chatx_t)(FILE *in);

static int encode_read_pair(FILE *in, char *a, char *b)
{
     int a_length;
     int b_length;
     char *z;

     if ( fgets(a, MAX_LINE, in) == NULL )
         return 0;

     z = strchr(a, '\n');
     if ( z == NULL )
     {
         fprintf(stderr, "Line too long.\n");
         exit(EXIT_FAILURE);
     }

     *z = '\0';
     a_length = z - a;

     if ( fgets(b, MAX_LINE, in) == NULL )
         b_length = 0;
     else
     {
         z = strchr(b, '\n');
         if ( z == NULL )
         {
             fprintf(stderr, "Line too long.\n");
             exit(EXIT_FAILURE);
         }

         *z = '\0';
         b_length = z - b;
     }

     if ( a_length == 0 )
     {
         a_length = 2;
         a[0] = 'x';
         a[1] = 'x';
         a[2] = '\0';
     }
     else
     {
         if ( a_length % 2 == 1 )
         {
             a[a_length++] = 'x';
             a[a_length] = '\0';
         }
     }

     if ( b_length == 0 )
     {
         b_length = 2;
         b[0] = 'x';
         b[1] = 'x';
         b[2] = '\0';
     }
     else
     {
         if ( b_length % 2 == 1 )
         {
             b[b_length++] = 'x';
             b[b_length] = '\0';
         }
     }

     if ( a_length > b_length )
     {
         for (int i=b_length; i<a_length; i++)
             b[i] = 'x';

         b_length = a_length;
         b[b_length] = '\0';
     }

     if ( b_length > a_length )
     {
         for (int i=a_length; i<b_length; i++)
             a[i] = 'x';

         a_length = b_length;
         a[a_length] = '\0';
     }

     return a_length;
}

static void chatx_encode(FILE *in)
{
     char a[MAX_LINE];
     char b[MAX_LINE];
     char c[MAX_LINE];
     char d[MAX_LINE];
     int length;
     char p,q,r,s;
     int c_pos;
     int d_pos;

     while (1)
     {
         c_pos = 0;
         d_pos = 0;

         if ( (length = encode_read_pair(in, a, b)) == 0 )
             break;

         for (int i=0; i<length; i+=2)
         {
             p = a[i];
             q = a[i+1];
             r = b[i];
             s = b[i+1];

             c[c_pos++] = r;
             c[c_pos++] = p;

             d[d_pos++] = s;
             d[d_pos++] = q;
         }

         c[length] = '\0';
         d[length] = '\0';

         puts(c);
         puts(d);
     }
}

static int decode_read_pair(FILE *in, char *a, char *b)
{
     int a_length;
     int b_length;
     char *z;

     if ( fgets(a, MAX_LINE, in) == NULL )
         return 0;

     z = strchr(a, '\n');
     if ( z == NULL )
     {
         fprintf(stderr, "Line too long.\n");
         exit(EXIT_FAILURE);
     }

     *z = '\0';
     a_length = z - a;

     if ( fgets(b, MAX_LINE, in) == NULL )
     {
         fprintf(stderr, "Expected pair of lines.\n");
         exit(EXIT_FAILURE);
     }

     z = strchr(b, '\n');
     if ( z == NULL )
     {
         fprintf(stderr, "Line too long.\n");
         exit(EXIT_FAILURE);
     }

     *z = '\0';
     b_length = z - b;

     if ( a_length != b_length )
     {
         fprintf(stderr, "Line pair has different lengths.");
         exit(EXIT_FAILURE);
     }

     if ( a_length % 2 != 0 )
     {
         fprintf(stderr,
             "Expected lines to be even number of characters.");
         exit(EXIT_FAILURE);
     }

     return a_length;
}

static void chatx_decode(FILE *in)
{
     char a[MAX_LINE];
     char b[MAX_LINE];
     char c[MAX_LINE];
     char d[MAX_LINE];
     int length;
     char p,q,r,s;
     int c_pos;
     int d_pos;

     while (1)
     {
         c_pos = 0;
         d_pos = 0;

         if ( (length = decode_read_pair(in, a, b)) == 0 )
             break;

         for (int i=0; i<length; i+=2)
         {
             p = a[i];
             q = a[i+1];
             r = b[i];
             s = b[i+1];

             c[c_pos++] = q;
             c[c_pos++] = s;

             d[d_pos++] = p;
             d[d_pos++] = r;
         }

         c[length] = '\0';
         d[length] = '\0';

         puts(c);
         puts(d);
     }
}

int main(int argc, char *argv[])
{
     chatx_t chatx = chatx_encode;

     if ( argc > 2 )
     {
         fprintf(stderr, "Usage: %s [-d]\n", argv[0]);
         return EXIT_FAILURE;
     }

     if ( argc == 2 )
     {
         if ( strcmp(argv[1], "-d") == 0 )
             chatx = chatx_decode;
         else
         {
             if ( strcmp(argv[1], "-e") == 0 )
                 chatx = chatx_encode;
             else
             {
                 fprintf(stderr, "Usage: %s [-d]\n", argv[0]);
                 return EXIT_FAILURE;
             }
         }
     }

     chatx(stdin);

     return 0;
}

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#50121

On 25/09/2021 13:56, Richard Harnden wrote:
> On 20/09/2021 10:17, Richard Heathfield wrote:
>> lFcrdtwo,econ you itelt nx
>> ook ohns  af you sdinliofy
>> ttie aegtrxtxmxuxex xoxexcxyt
>> hhs tlxo?ixhx xsxdxtx xnxrxpx
>> tFar eat apcrexim,tc t semr poexx
>> hot cxnra prodita eua doceyctdion
>> a-t sa.dxrxtxax xtxlxoxsx xsxIxcn
>> t-ehtrxex xhxnxix xoxkx,xax x xax
>> eAed danptns yenetxig
>> vnr hop'e sah ro.hxnx
>>
> 
> Here's my chatx encoder/decoder effort.
> I spent far too much time on this.
> 
> 
> #include <stdio.h>
> #include <stdlib.h>
> #include <string.h>
> 
> #define MAX_LINE 1024
> 
> typedef void (*chatx_t)(FILE *in);
> 
> static int encode_read_pair(FILE *in, char *a, char *b)
> {
>      int a_length;
>      int b_length;
>      char *z;
> 
>      if ( fgets(a, MAX_LINE, in) == NULL )
>          return 0;
> 
>      z = strchr(a, '\n');
>      if ( z == NULL )
>      {
>          fprintf(stderr, "Line too long.\n");
>          exit(EXIT_FAILURE);
>      }
> 
>      *z = '\0';
>      a_length = z - a;
> 
>      if ( fgets(b, MAX_LINE, in) == NULL )
>          b_length = 0;
>      else
>      {
>          z = strchr(b, '\n');
>          if ( z == NULL )
>          {
>              fprintf(stderr, "Line too long.\n");
>              exit(EXIT_FAILURE);
>          }
> 
>          *z = '\0';
>          b_length = z - b;
>      }
> 
>      if ( a_length == 0 )
>      {
>          a_length = 2;
>          a[0] = 'x';
>          a[1] = 'x';
>          a[2] = '\0';
>      }
>      else
>      {
>          if ( a_length % 2 == 1 )
>          {
>              a[a_length++] = 'x';
>              a[a_length] = '\0';
>          }
>      }
> 
>      if ( b_length == 0 )
>      {
>          b_length = 2;
>          b[0] = 'x';
>          b[1] = 'x';
>          b[2] = '\0';
>      }
>      else
>      {
>          if ( b_length % 2 == 1 )
>          {
>              b[b_length++] = 'x';
>              b[b_length] = '\0';
>          }
>      }
> 
>      if ( a_length > b_length )
>      {
>          for (int i=b_length; i<a_length; i++)
>              b[i] = 'x';
> 
>          b_length = a_length;
>          b[b_length] = '\0';
>      }
> 
>      if ( b_length > a_length )
>      {
>          for (int i=a_length; i<b_length; i++)
>              a[i] = 'x';
> 
>          a_length = b_length;
>          a[a_length] = '\0';
>      }
> 
>      return a_length;
> }
> 
> static void chatx_encode(FILE *in)
> {
>      char a[MAX_LINE];
>      char b[MAX_LINE];
>      char c[MAX_LINE];
>      char d[MAX_LINE];
>      int length;
>      char p,q,r,s;
>      int c_pos;
>      int d_pos;
> 
>      while (1)
>      {
>          c_pos = 0;
>          d_pos = 0;
> 
>          if ( (length = encode_read_pair(in, a, b)) == 0 )
>              break;
> 
>          for (int i=0; i<length; i+=2)
>          {
>              p = a[i];
>              q = a[i+1];
>              r = b[i];
>              s = b[i+1];
> 
>              c[c_pos++] = r;
>              c[c_pos++] = p;
> 
>              d[d_pos++] = s;
>              d[d_pos++] = q;
>          }
> 
>          c[length] = '\0';
>          d[length] = '\0';
> 
>          puts(c);
>          puts(d);
>      }
> }
> 
> static int decode_read_pair(FILE *in, char *a, char *b)
> {
>      int a_length;
>      int b_length;
>      char *z;
> 
>      if ( fgets(a, MAX_LINE, in) == NULL )
>          return 0;
> 
>      z = strchr(a, '\n');
>      if ( z == NULL )
>      {
>          fprintf(stderr, "Line too long.\n");
>          exit(EXIT_FAILURE);
>      }
> 
>      *z = '\0';
>      a_length = z - a;
> 
>      if ( fgets(b, MAX_LINE, in) == NULL )
>      {
>          fprintf(stderr, "Expected pair of lines.\n");
>          exit(EXIT_FAILURE);
>      }
> 
>      z = strchr(b, '\n');
>      if ( z == NULL )
>      {
>          fprintf(stderr, "Line too long.\n");
>          exit(EXIT_FAILURE);
>      }
> 
>      *z = '\0';
>      b_length = z - b;
> 
>      if ( a_length != b_length )
>      {
>          fprintf(stderr, "Line pair has different lengths.");
>          exit(EXIT_FAILURE);
>      }
> 
>      if ( a_length % 2 != 0 )
>      {
>          fprintf(stderr,
>              "Expected lines to be even number of characters.");
>          exit(EXIT_FAILURE);
>      }
> 
>      return a_length;
> }
> 
> static void chatx_decode(FILE *in)
> {
>      char a[MAX_LINE];
>      char b[MAX_LINE];
>      char c[MAX_LINE];
>      char d[MAX_LINE];
>      int length;
>      char p,q,r,s;
>      int c_pos;
>      int d_pos;
> 
>      while (1)
>      {
>          c_pos = 0;
>          d_pos = 0;
> 
>          if ( (length = decode_read_pair(in, a, b)) == 0 )
>              break;
> 
>          for (int i=0; i<length; i+=2)
>          {
>              p = a[i];
>              q = a[i+1];
>              r = b[i];
>              s = b[i+1];
> 
>              c[c_pos++] = q;
>              c[c_pos++] = s;
> 
>              d[d_pos++] = p;
>              d[d_pos++] = r;
>          }
> 
>          c[length] = '\0';
>          d[length] = '\0';
> 
>          puts(c);
>          puts(d);
>      }
> }
> 
> int main(int argc, char *argv[])
> {
>      chatx_t chatx = chatx_encode;
> 
>      if ( argc > 2 )
>      {
>          fprintf(stderr, "Usage: %s [-d]\n", argv[0]);
>          return EXIT_FAILURE;
>      }
> 
>      if ( argc == 2 )
>      {
>          if ( strcmp(argv[1], "-d") == 0 )
>              chatx = chatx_decode;
>          else
>          {
>              if ( strcmp(argv[1], "-e") == 0 )
>                  chatx = chatx_encode;
>              else
>              {
>                  fprintf(stderr, "Usage: %s [-d]\n", argv[0]);
>                  return EXIT_FAILURE;
>              }
>          }
>      }
> 
>      chatx(stdin);
> 
>      return 0;
> }
> 

I tried it on the puzzle ciphertext and came across an oddity.


rjh@here$ ./hdc < t3.cipher
olkcodnw ,ac noy udineitfn
oF rhtso efoy uos itllo yx
htsit xe?txxxxxxxxxxxxxxxxxxxt
ht elaogirht msudet  onercpyxx
httac naa pporixameta d ceyrtpienx
oF rxert arcdeti ,uc tosemc dooxxx
taettsx.xxxxxxxxxxxxxxxxxxxxxxxxxn
--h raed rhtnai  tolko,sa  s Iacxx
vereh paepsnh re.exxxg
nA dod'n tas yonhtnixx
rjh@here$ cat t3.cipher | wc -l
10
rjh@here:~/alldata/dev/crypto/sqspin/harndendecrypt$ ./hdc -d < t3.cipher
For those of you still oxy
lockdown, can you identinf
Expected lines to be even number of characters.

Last I checked, 10 is even. :-)


NO! For heaven's sake don't waste time fixing it on my account. My 
decoder's screwed too and I'm letting it go.

-- 
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

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#50122

On 25/09/2021 14:21, Richard Heathfield wrote:
> I tried it on the puzzle ciphertext and came across an oddity.
> 
> 
> rjh@here$ ./hdc < t3.cipher

I didn't mean to post that!

Broadly:

Step 1: wc -l reports 10 lines of ciphertext.
Step 2: Richard Harnden's decoder reports odd number of lines.
Step 3: Contemplate that Richard Heathfield's decoder is screwed too.
Step 4: Break open a beer.

-- 
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

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#50123

Op 25-9-2021 om 14:56 schreef Richard Harnden:
> On 20/09/2021 10:17, Richard Heathfield wrote:
>> lFcrdtwo,econ you itelt nx
>> ook ohns  af you sdinliofy
>> ttie aegtrxtxmxuxex xoxexcxyt
>> hhs tlxo?ixhx xsxdxtx xnxrxpx
>> tFar eat apcrexim,tc t semr poexx
>> hot cxnra prodita eua doceyctdion
>> a-t sa.dxrxtxax xtxlxoxsx xsxIxcn
>> t-ehtrxex xhxnxix xoxkx,xax x xax
>> eAed danptns yenetxig
>> vnr hop'e sah ro.hxnx
>>
> 
> Here's my chatx encoder/decoder effort.
> I spent far too much time on this.

That's a bit inherit to accepting these kind of tasks.
I tried your version (reading from stdin and encrypt) and it seems to be 
compatible with my decrypt. So just to let you know it compiles on my 
system and has been run  by at least 3 people now. Your time has not 
been wasted ;-) (as a side effect I had to install gcc in my WSL which 
is good use of my time as well).

Ozz

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