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Article #940

Re: pgp2.0 signature security problem

#940
From: Mark Henderson
Date: Mon, 14 Sep 1992 19:17
55 lines
2144 bytes
In article <1992Sep12.174358.11564@colnet.cmhnet.org> res@colnet.cmhnet.org (Rob Stampfli) writes:
>I recently had a chance to play around with pgp2.0 on a sVr2 Unix machine.
>There appears to be a big security problem with the signature mechanism:
>If you "sign" a file, and then add additional information to the end of
>the signed file, pgp includes this additional information as part of what
>it says you signed.  For instance:
>
>echo 1 2 3 4 5 | pgp -fs >xyzzy.pgp
>echo 6 7 8 9 10 >>xyzzy.pgp
>pgp xyzzy.pgp
>
>pgp now tells me I have signed the phrase:
>
>	1 2 3 4 5
>	6 7 8 9 10
>
>when I have in fact only signed the first line.
>-- 
>Rob Stampfli  rob@colnet.cmhnet.org      The neat thing about standards:
>614-864-9377  HAM RADIO: kd8wk@n8jyv.oh  There are so many to choose from.

The following may be a fix. I haven't tested it extensively, it may
very well screw something else up.

Mark

*** crypto.c.orig	Mon Sep 14 10:31:12 1992
--- crypto.c	Mon Sep 14 10:31:48 1992
***************
*** 1494,1505 ****
  		}
  		CONVERSION = (lit_mode == MODE_TEXT) ? EXT_CONV : NO_CONV;
  #ifdef CANONICAL_TEXT
! 		copyfile(f,g,-1L);	/* copy rest of file from file f to g */
  #else
  		if (lit_mode == MODE_BINARY)
! 			copyfile( f, g, -1L );
  		else
! 			copyfile_from_canon( f, g, -1L );
  #endif
  		CONVERSION = NO_CONV;
  
--- 1494,1505 ----
  		}
  		CONVERSION = (lit_mode == MODE_TEXT) ? EXT_CONV : NO_CONV;
  #ifdef CANONICAL_TEXT
! 		copyfile(f,g,text_len);	/* copy rest of file from file f to g */
  #else
  		if (lit_mode == MODE_BINARY)
! 			copyfile( f, g, text_len );
  		else
! 			copyfile_from_canon( f, g, text_len );
  #endif
  		CONVERSION = NO_CONV;
  
Technical Details
Message-ID: <#yynvxl.henderso@netcom.com>
Path: arc1-ca.pugleaf.net!sparky!uunet!zaphod.mps.ohio-state.edu!darwin.sura.net!spool.mu.edu!umn.edu!csus.edu!netcom.com!henderso
References: <1992Sep12.174358.11564@colnet.cmhnet.org>

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Newsgroups: sci.crypt,alt.security
Path: arc1-ca.pugleaf.net!sparky!uunet!zaphod.mps.ohio-state.edu!darwin.sura.net!spool.mu.edu!umn.edu!csus.edu!netcom.com!henderso
From: henderso@netcom.com (Mark Henderson)
Subject: Re: pgp2.0 signature security problem
Message-ID: <#yynvxl.henderso@netcom.com>
Date: Mon, 14 Sep 92 19:17:32 GMT
Organization: Netcom
References: <1992Sep12.174358.11564@colnet.cmhnet.org>
Lines: 55