Todd Zullinger tmz at
Wed Jan 23 20:47:27 CET 2008

McDougall, Marshall (STEM) wrote:
> Hi All.
> First gentle :-}
> I have a RHEL server and I am having difficulty decrypting a pgp
> encrypted file.  Near as I can tell, I need the IDEA cipher.  
> [user at myserver]# gpg --decrypt myfile.txt 
> gpg: protection algorithm 1 (IDEA) is not supported
> gpg: the IDEA cipher plugin is not present
> gpg: please see for more
> information
> gpg: encrypted with 1024-bit RSA key, ID C0A298D3, created 2004-07-13
>      "one_of_my_keys"
> gpg: public key decryption failed: unknown cipher algorithm
> gpg: decryption failed: secret key not available
> I roamed around the GNUPG site and found the "idea.c.gz" downloads, but
> the instructions allude to directories that don't exist on my server.
> Has anyone added IDEA to an existing canned redhat installation?  I am
> open to any suggestion.  Thanks.

You can rebuild the gnupg srpm and add idea.  A few small changes to
the spec file (like in the attached diff) should do what you want.

A better solution would be to have sender encrypt the file to you
using a cipher that you can use without any patents or other
encumbrances.  Does your key have a cipher pref for IDEA?  If so, you
should fix that so other people don't encrypt things to you that you
can't easily decrypt.  You can view your prefs with:

$ gpg --edit-key C0A298D3 showpref quit

Todd        OpenPGP -> KeyID: 0xBEAF0CE3 | URL:
I never met a morphosis I didn't like.

-------------- next part --------------
--- gnupg.spec~	2007-03-01 07:47:37.000000000 -0500
+++ gnupg.spec	2008-01-23 14:40:16.000000000 -0500
@@ -1,12 +1,13 @@
 Summary: A GNU utility for secure communication and data storage.
 Name: gnupg
 Version: 1.4.5
-Release: 13
+Release: 13.1
 License: GPL
 Group: Applications/System
 Source2: gnupg-shm-coprocessing.expect
 Patch0: gnupg-1.4.1-gcc.patch
 Patch1: gnupg-1.4.2-curl.patch
 Patch2: gnupg-1.4.5-CVE-2006-6169.patch
@@ -42,6 +43,7 @@
 %patch4 -p0 -b .CVE-2006-6235
 %patch5 -p2 -b .multiple-message
+gunzip -c %{SOURCE3} > cipher/idea.c
@@ -109,6 +111,9 @@
+* Wed Jan 23 2008 Todd Zullinger <tmz at> - 1.4.5-13.1
+- include the IDEA cipher
 * Thu Mar  1 2007 Nalin Dahyabhai <nalin at> - 1.4.5-13
 - incorporate patch from Werner to work around clients which
   can't tell that multiple plain messages have been processed (#230457)
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