GNU bug report logs - #60693
30.0.50; gnutls-symmetric-encrypt/decrypt in GCM mode requires plaintext/ciphertext size to be multiple of 16

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Jürgen Hötzel <juergen <at> hoetzel.info>
To: bug-gnu-emacs <at> gnu.org
Subject: 30.0.50; gnutls-symmetric-encrypt/decrypt in GCM mode requires
 plaintext/ciphertext size to be multiple of 16
Date: Mon, 09 Jan 2023 19:06:52 +0100

(gnutls-symmetric-encrypt 'AES-128-GCM "0123456789ABCDEF" "0123456789AB"
"hello")

results in:

(error "GnuTLS AEAD cipher AES-128-GCM/encrypt input block length 5 is
not 0 greater than a multiple of the required 16")


GCM doesn't require any padding of the plaintext before it is used, so this is
IMO an invalid assumption. Evaluating


The corresponding C code using GnuTLS works as expected:

#include <gnutls/crypto.h>
#include <gnutls/gnutls.h>
#include <stdio.h>

int main(int argc, char *argv[]) {
  gnutls_datum_t key = {.data = (unsigned char *)"0123456789ABCDEF", .size = 16};
  char iv[12] = "0123456789AB";
  char plaintext[5] = "hello";
  int tlserr;
  gnutls_session_t session;
  gnutls_aead_cipher_hd_t hd;
  if ((tlserr = gnutls_init(&session, 0) != GNUTLS_E_SUCCESS)) {
  };

  if (gnutls_aead_cipher_init(&hd, GNUTLS_CIPHER_AES_128_GCM, &key) < 0) {
    fprintf(stderr, "gnutls_cipher_init failed: %s", gnutls_strerror(tlserr));
    goto cleanup;
  }
  char ctext[5 + 16]; /* plaintext + tagsize */
  size_t ctext_len = 5 + 16;
  if ((tlserr = gnutls_aead_cipher_encrypt(hd, iv, sizeof(iv), NULL, 0, 16, plaintext, 5, ctext, &ctext_len)) < 0) {
    fprintf(stderr, "gnutls_aead_cipher_decrypt failed: %s\n", gnutls_strerror(tlserr));
    goto cleanup;
  }
  fwrite(ctext, 1, ctext_len, stdout);
cleanup:
  gnutls_deinit(session);
  return tlserr;
}

Best regards,

Jürgen

GnuTLS-Version used: gnutls 3.7.8-4

In GNU Emacs 30.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version
 3.24.35, cairo version 1.17.6) of 2023-01-08 built on herakles
Repository revision: 0be40fbe43c4e409a417b12d2919ca64326e0281
Repository branch: master
System Description: Arch Linux

Configured using:
 'configure --prefix /home/juergen/emacs/emacs-master 'CFLAGS=-g -O0''

Configured features:
ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM GSETTINGS HARFBUZZ JPEG
JSON LCMS2 LIBOTF LIBSYSTEMD LIBXML2 M17N_FLT MODULES NOTIFY INOTIFY
PDUMPER PNG RSVG SECCOMP SOUND SQLITE3 THREADS TIFF TOOLKIT_SCROLL_BARS
WEBP X11 XDBE XIM XINPUT2 XPM GTK3 ZLIB

Important settings:
  value of $LANG: de_DE.utf8
  locale-coding-system: utf-8-unix

Major mode: ELisp/l

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  eldoc-mode: t
  show-paren-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
  line-number-mode: t
  indent-tabs-mode: t
  transient-mark-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message mailcap yank-media rfc822 mml
mml-sec password-cache epa derived epg rfc6068 epg-config gnus-util
text-property-search time-date subr-x mm-decode mm-bodies mm-encode
mail-parse rfc2231 mailabbrev gmm-utils mailheader sendmail rfc2047
rfc2045 ietf-drums mm-util mail-prsvr mail-utils help-fns radix-tree
cl-print debug backtrace help-mode find-func gnutls puny dired-aux
cl-loaddefs cl-lib dired dired-loaddefs term/xterm xterm byte-opt gv
bytecomp byte-compile rmc iso-transl tooltip cconv eldoc paren electric
uniquify ediff-hook vc-hooks lisp-float-type elisp-mode mwheel
term/x-win x-win term/common-win x-dnd tool-bar dnd fontset image
regexp-opt fringe tabulated-list replace newcomment text-mode lisp-mode
prog-mode register page tab-bar menu-bar rfn-eshadow isearch easymenu
timer select scroll-bar mouse jit-lock font-lock syntax font-core
term/tty-colors frame minibuffer nadvice seq simple cl-generic
indonesian philippine 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
composite emoji-zwj charscript charprop case-table epa-hook
jka-cmpr-hook help abbrev obarray oclosure cl-preloaded button loaddefs
theme-loaddefs faces cus-face macroexp files window text-properties
overlay sha1 md5 base64 format env code-pages mule custom widget keymap
hashtable-print-readable backquote threads dbusbind inotify lcms2
dynamic-setting system-font-setting font-render-setting cairo
move-toolbar gtk x-toolkit xinput2 x multi-tty make-network-process
emacs)

Memory information:
((conses 16 55112 8296)
 (symbols 48 6511 0)
 (strings 32 17575 2110)
 (string-bytes 1 510603)
 (vectors 16 9803)
 (vector-slots 8 119382 8254)
 (floats 8 27 295)
 (intervals 56 752 35)
 (buffers 976 16))

Message #10 received at 60693-done <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Jürgen Hötzel <juergen <at> hoetzel.info>
Cc: 60693-done <at> debbugs.gnu.org
Subject: Re: bug#60693: 30.0.50;
 gnutls-symmetric-encrypt/decrypt in GCM mode requires
 plaintext/ciphertext size to be multiple of 16
Date: Mon, 09 Jan 2023 22:19:21 +0200

> From: Jürgen Hötzel <juergen <at> hoetzel.info>
> Date: Mon, 09 Jan 2023 19:06:52 +0100
> 
> (gnutls-symmetric-encrypt 'AES-128-GCM "0123456789ABCDEF" "0123456789AB"
> "hello")
> 
> results in:
> 
> (error "GnuTLS AEAD cipher AES-128-GCM/encrypt input block length 5 is
> not 0 greater than a multiple of the required 16")
> 
> 
> GCM doesn't require any padding of the plaintext before it is used, so this is
> IMO an invalid assumption. Evaluating

OK, thanks.  I disabled the check on the master branch, and closing
the bug.

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