GPG Decryption fails for files > 1MB

Werner Koch wk at
Fri Apr 13 16:27:58 CEST 2012

On Thu, 12 Apr 2012 10:49, david.vazquez_landa at said:

> We have an issue with one of our users. When he sends encrypted messages larger than ~1 MB, we get these errors:

> gpg: [don't know]: invalid packet (ctb=0d)

> gpg: [don't know]: invalid packet (ctb=0a)

This might indicate a problem in your file transfer - make sure data is
not modified; i.e. the channel is 8 bit clean).  As a quick test you may
add the option --armor to the encryption command - this makes the
message larger but it will be plain ASCII.

> $ /cygdrive/d/GNU/GnuPG/gpg.exe --version
> gpg (GnuPG) 1.4.8

I don't know whether you use a version of GPG build for Cygwin - I
suggest to use a native Windows version of GnuPG - and well; update to
a more recent version <>

> Is this a gnupg bug?

I doubt that.  If you need support, you may want to checkout the service
directory at



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