-----BEGIN PGP SIGNED MESSAGE----- I found a bug in pgp 2.3a : it's incompatible with pgp 2.6 messages made after September first. Here's the fix, in both uuencode and pgp armored format. Uudecode or pgp-extract this, and you will get a file called fixpgp.com. Go into the directory where your pgp 2.3a DOS executable is (pgp.exe) and run fixpgp. It should print "Done". That's it! 2.3a is now fully compatible with 2.6. If it prints "File error" pgp.exe is either not present or not writable. Fixpgp must be run with pgp.exe in the current directory. Do not run on anything but a virgin copy of the pgp23a for dos distribution. If you compiled it yourself, modify the source as described below. Pr0duct Cypher section 1 of uuencode 4.13 of file FIXPGP.COM begin 644 FIXPGP.COM MN`(]NCL!S2%R*(O8N`!"N0``NH?"S2%R&;1`N0$`NE,!S2%R#;0^S2&T";I.W G`<TAS2"T";I#`<TAS2!P9W`N97AE`$9I;&4@97)R;W(D1&]N920&7 `` end sum -r/size 47444/146 section (from "begin" to "end") sum -r/size 46454/84 entire input file - -----BEGIN PGP MESSAGE----- Version: 2.3a rGRiCmZpeHBncC5jb20AAAAAuAI9ujsBzSFyKIvYuABCuQAAuofCzSFyGbRAuQEA ulMBzSFyDbQ+zSG0CbpOAc0hzSC0CbpDAc0hzSBwZ3AuZXhlAEZpbGUgZXJyb3Ik RG9uZSQG =4Xbh - -----END PGP MESSAGE----- Now, wait a minute! This sounds like an evil NSA plot to compromise PGP! What, exactly, will this program do to my PGP? The short answer: it changes the byte at file offset C287 hex from a 08 hex to a 06 hex. The long answer: take a look at crypto.c and we find: /* Return nonzero if val doesn't match checkval, after printing a * warning. */ int version_error(int val, int checkval) { if (val != checkval) { fprintf (pgpout, PSTR( "\n\007Unsupported packet format - you need a newer version\ of PGP for this file.\n")); return(1); } return(0); } We need to disable this comparison. So looking at the object code: (CS at startup was 136D) 1B8B:069F 55 PUSH BP 1B8B:06A0 8BEC MOV BP,SP 1B8B:06A2 8B4606 MOV AX,[BP+06] 1B8B:06A5 3B4608 CMP AX,[BP+08] 1B8B:06A8 7424 JZ 06CE 1B8B:06AA 1E PUSH DS 1B8B:06AB B8C00F MOV AX,0FC0 1B8B:06AE 50 PUSH AX 1B8B:06AF 9A6A04412E CALL 2E41:046A There's our comparison. [bp+06] and [bp+08] are val and checkval. So if we change the [bp+08] in the cmp to [bp+06], the program compares [bp+06] to itself. This will always be true, so PGP will not notice the fact that the packet number has changed to 03 from 02. Problem solved. This is the source for fixpgp.com. I used the a86 assembler. BTW note that PGPTools does not check version numbers, so it is always compatible with 2.6. ; fixpgp.com : writes 06 hex to byte c287 of pgp2.3a ; this fixes 2.6 incompatibility org 100h mov ax,03d02 ; r/w mov dx,fname ; filename int 21h ; open file jc error ; check for error mov bx,ax ; move file handle mov ax,04200 ; file seek mov cx,0 ; msw of offset mov dx,0c287h ; magic address int 21h ; move file pointer jc error ; check for error mov ah,040h ; write file mov cx,1 ; one byte mov dx,offset magic ; byte to write int 21h ; write the byte jc error ; check for error mov ah,03eh ; close file int 21h ; do it mov ah,09h ; print msg mov dx,okmsg ; it worked int 21h ; print int 20h ; and quit error: mov ah,09h ; print msg mov dx,ermsg ; adr of msg int 21h ; print the error int 20h ; abort fname: db 'pgp.exe',0 ermsg: db 'File error$' okmsg: db 'Done$' magic: db 06h -----BEGIN PGP SIGNATURE----- Version: 2.3a lives! iQCVAgUBLeGxH8GoFIWXVYodAQGH9wQAhLGL4V/86DMTjw4qlfJd0gbQCAf+sFSC Hpf9jD1YAdUfUMRGYvp+8wNVBv9z90EHppRkU7MOT8zFJ3F0uJHvbzQgiiWp/5tO nyimv9D4lotqg/K7wmQwCEmys0sj0/zLOyyzAX/62YX8rmLKfTCo88V94QdEaNHS boBMlUSX0ys= =pVKf -----END PGP SIGNATURE-----