bug#28780: 25.3; Bad signature from GNU ELPA whe coding-system-for-read is utf-8

[Iakov Davydov <dav02.davs@myths.ru>]

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When installing a package (e.g. auctex), an error message appears:
Failed to verify signature auctex-11.91.0.tar.sig:
Bad signature from 474F05837FBDEF9B GNU ELPA Signing Agent <
elpasign@elpa.gnu.org>
Command output:
gpg: [don't know]: indeterminate length for invalid packet type 14
gpg: Signature made Tue 25 Jul 2017 11:10:02 PM CEST using DSA key ID
7FBDEF9B
gpg: BAD signature from "GNU ELPA Signing Agent <elpasign@elpa.gnu.org>"
[unknown]


This only happens if the following line in my .emacs:
(setq-default coding-system-for-read 'utf-8)


Steps to reproduce:

1. Run emacs -Q
2. Execute `(setq-default coding-system-for-read 'utf-8)` (e.g. go to
scratch, type this command, type C-x C-e).
3. M-x package-install auctex
4. Error message appears.

If step #2 is skipped, installation happens without an error.

In fact, this or similar problem seems to be quite common, but often
cannot be reproduced.
1. emacs bug#22971
2. https://emacs.stackexchange.com/questions/10046
3. https://github.com/jacksonrayhamilton/tern-context-coloring/issues/4
4. https://github.com/ananthakumaran/tide/issues/51
5. https://github.com/syl20bnr/spacemacs/issues/3669
6. https://www.reddit.com/r/emacs/comments/6t21lb/
7. https://www.linux.org.ru/forum/security/13718006 (In Russian)
...



In GNU Emacs 25.3.2 (x86_64-pc-linux-gnu, GTK+ Version 3.18.9)
 of 2017-09-12 built on lcy01-32
Windowing system distributor 'The X.Org Foundation', version 11.0.11804000
System Description: Ubuntu 16.04.3 LTS

Configured using:
 'configure --build=x86_64-linux-gnu --prefix=/usr
 '--includedir=${prefix}/include' '--mandir=${prefix}/share/man'
 '--infodir=${prefix}/share/info' --sysconfdir=/etc --localstatedir=/var
 --disable-silent-rules '--libdir=${prefix}/lib/x86_64-linux-gnu'
 '--libexecdir=${prefix}/lib/x86_64-linux-gnu' --disable-maintainer-mode
 --disable-dependency-tracking --prefix=/usr --sharedstatedir=/var/lib
 --program-suffix=25 --with-modules --with-x=yes --with-x-toolkit=gtk3
 'CFLAGS=-g -O2 -fstack-protector-strong -Wformat
 -Werror=format-security' 'CPPFLAGS=-Wdate-time -D_FORTIFY_SOURCE=2'
 'LDFLAGS=-Wl,-Bsymbolic-functions -Wl,-z,relro''

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND GPM DBUS GCONF GSETTINGS
NOTIFY LIBSELINUX GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11 MODULES

Important settings:
  value of $LC_MONETARY: en_US.UTF-8
  value of $LC_NUMERIC: en_US.UTF-8
  value of $LC_TIME: en_US.UTF-8
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Making completion list... [4 times]

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message dired format-spec rfc822 mml
mml-sec password-cache epg epg-config gnus-util mm-decode mm-bodies
mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader sendmail
rfc2047 rfc2045 ietf-drums mm-util help-fns help-mode easymenu
cl-loaddefs pcase cl-lib mail-prsvr mail-utils time-date mule-util
tooltip eldoc electric uniquify ediff-hook vc-hooks lisp-float-type
mwheel x-win term/common-win x-dnd tool-bar dnd fontset image regexp-opt
fringe tabulated-list newcomment elisp-mode lisp-mode prog-mode register
page menu-bar rfn-eshadow timer select scroll-bar mouse jit-lock
font-lock syntax facemenu font-core frame cl-generic cham georgian
utf-8-lang misc-lang vietnamese tibetan thai tai-viet lao korean
japanese eucjp-ms cp51932 hebrew greek romanian slovak czech european
ethiopic indian cyrillic chinese charscript case-table epa-hook
jka-cmpr-hook help simple abbrev minibuffer cl-preloaded nadvice
loaddefs button faces cus-face macroexp files text-properties overlay
sha1 md5 base64 format env code-pages mule custom widget
hashtable-print-readable backquote dbusbind inotify dynamic-setting
system-font-setting font-render-setting move-toolbar gtk x-toolkit x
multi-tty make-network-process emacs)

Memory information:
((conses 16 89919 7124)
 (symbols 48 19970 0)
 (miscs 40 701 121)
 (strings 32 15204 4512)
 (string-bytes 1 450810)
 (vectors 16 12462)
 (vector-slots 8 445519 6009)
 (floats 8 167 30)
 (intervals 56 242 1)
 (buffers 976 19)
 (heap 1024 38793 1016))

-- 
Iakov Davydov
Postdoc, Department of Computational Biology and Department of Ecology and
Evolution, University of Lausanne
Swiss Institute of Bioinformatics

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