Subject: bug#60693: closed (Re: bug#60693: 30.0.50; gnutls-symmetric-encrypt/decrypt in GCM mode requires plaintext/ciphertext size to be multiple of 16)

From: [email-masked] (GNU bug Tracking System)
Date: Mon, 09 Jan 2023 20:20:02 +0000

Your bug report

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

which was filed against the emacs package, has been closed.

The explanation is attached below, along with your original report.
If you require more details, please reply to [email-masked].

-- 
60693: https://debbugs.gnu.org/cgi/bugreport.cgi?bug=60693
GNU Bug Tracking System
Contact [email-masked] with problems

Subject: Re: bug#60693: 30.0.50; gnutls-symmetric-encrypt/decrypt in GCM mode requires plaintext/ciphertext size to be multiple of 16
From: Eli Zaretskii <[email-masked]>
To: Jürgen Hötzel <[email-masked]>
Cc: [email-masked]
Date: Mon, 09 Jan 2023 22:19:21 +0200
List-Id: <debbugs-submit.debbugs.gnu.org>

> From: Jürgen Hötzel <[email-masked]>
> 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.

Subject: 30.0.50; gnutls-symmetric-encrypt/decrypt in GCM mode requires plaintext/ciphertext size to be multiple of 16
From: Jürgen Hötzel <[email-masked]>
To: [email-masked]
Date: Mon, 09 Jan 2023 19:06:52 +0100
List-Id: <debbugs-submit.debbugs.gnu.org>

(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
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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:
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  line-number-mode: t
  indent-tabs-mode: t
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  auto-composition-mode: t
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Load-path shadows:
None found.

Features:
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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)
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