ebcdic problem in bufaux.c

[Markus Friedl]

On Thu, Jul 22, 2004 at 01:36:06PM -0700, Greg Lambert wrote:
> I am working on a port of Openssh 3.8p1 after already
> having done a port of Openssh 3.5p1.  There are a
> couple of new lines in buffer_get_bignum2() that are
> causing me problems:
> 
>         if (len > 0 && (bin[0] & 0x80))
>                 fatal("buffer_get_bignum2: negative
> numbers not supported");
> 
> The "& 0x80" check is not relevant in ebcdic.  
>  
> Does anyone know why this check was added?

because negative numbers are not supported by
our buffer_get_bignum2.

see below

> What are the consequences of removing it?
>  
> Does anyone have any idea how I could get the same
> result as this check in ebcdic?

bin[] is not a character, it's just a byte.

here's a quote from the secsh-architecture draft:

   mpint

      Represents multiple precision integers in two's complement format,
      stored as a string, 8 bits per byte, MSB first. Negative numbers
      have the value 1 as the most significant bit of the first byte of
      the data partition. If the most significant bit would be set for a
      positive number, the number MUST be preceded by a zero byte.
      Unnecessary leading bytes with the value 0 or 255 MUST NOT be
      included.  The value zero MUST be stored as a string with zero
      bytes of data.

      By convention, a number that is used in modular computations in
      Z_n SHOULD be represented in the range 0 <= x < n.

       Examples:
       value (hex)        representation (hex)
       ---------------------------------------------------------------
       0                  00 00 00 00
       9a378f9b2e332a7    00 00 00 08 09 a3 78 f9 b2 e3 32 a7
       80                 00 00 00 02 00 80
       -1234              00 00 00 02 ed cc
       -deadbeef          00 00 00 05 ff 21 52 41 11