Verify signature for S/Mime?

[Tokariew]

set crypt_use_gpgme=yes
set crypt_autosign = yes
set crypt_verify_sig = yes

I added following lines to mine muttrc file
I can sign using mine pgp key, and verify others signatures, but when trying to verify email signed with S/Mime neomutt give me
Invoking S/MIME and after some time S/MIME signature could NOT be verified

What i'm missing to verify S/Mime signatures with gpgme?

I installed neomutt from Fedora COPR

[marvinwankersteen]

I have noticed the same thing and have not yet found a solution.

Tried also set smime_ca_location = "/etc/ssl/certs/ca-certificates.crt".

NeoMutt 20211029
Copyright (C) 1996-2020 Michael R. Elkins and others.
NeoMutt comes with ABSOLUTELY NO WARRANTY; for details type 'neomutt -vv'.
NeoMutt is free software, and you are welcome to redistribute it
under certain conditions; type 'neomutt -vv' for details.

System: Linux 5.15.0-86-generic (x86_64)
ncurses: ncurses 6.3.20211021 (compiled with 6.3.20211021)
libidn: 1.38 (compiled with 1.38)
GPGME: 1.14.0-unknown
GnuTLS: 3.7.2
libnotmuch: 5.5.0
storage: tokyocabinet

Configure options: --build=x86_64-linux-gnu --prefix=/usr {--includedir=${prefix}/include} {--mandir=${prefix}/share/man} {--infodir=${prefix}/share/info} --sysconfdir=/etc --localstatedir=/var --disable-option-checking --disable-silent-rules {--libdir=${prefix}/lib/x86_64-linux-gnu} --runstatedir=/run --disable-maintainer-mode --disable-dependency-tracking --mandir=/usr/share/man --libexecdir=/usr/libexec --with-mailpath=/var/mail --gpgme --lua --notmuch --with-ui --gnutls --gss --idn --mixmaster --sasl --tokyocabinet --sqlite --autocrypt

Compilation CFLAGS: -g -O2 -ffile-prefix-map=/build/neomutt-Y7QiPm/neomutt-20211029+dfsg1=. -flto=auto -ffat-lto-objects -fstack-protector-strong -Wformat -Werror=format-security -std=c99 -D_ALL_SOURCE=1 -D_GNU_SOURCE=1 -D__EXTENSIONS__ -I/usr/include -I/usr/include/lua5.4 -DNCURSES_WIDECHAR -isystem /usr/include/mit-krb5

Default options:
  +attach_headers_color +compose_to_sender +compress +cond_date +debug 
  +encrypt_to_self +forgotten_attachments +forwref +ifdef +imap +index_color 
  +initials +limit_current_thread +multiple_fcc +nested_if +new_mail +nntp +pop 
  +progress +quasi_delete +regcomp +reply_with_xorig +sensible_browser +sidebar 
  +skip_quoted +smtp +status_color +timeout +tls_sni +trash 

Compile options:
  +autocrypt +fcntl -flock -fmemopen +futimens +getaddrinfo +gnutls +gpgme +gss 
  +hcache -homespool +idn +inotify -locales_hack +lua +mixmaster +nls +notmuch 
  -openssl +pgp +regex +sasl +smime +sqlite +sun_attachment 

MAILPATH="/var/mail"
MIXMASTER="mixmaster"
PKGDATADIR="/usr/share/neomutt"
SENDMAIL="/usr/sbin/sendmail"
SYSCONFDIR="/etc"

To learn more about NeoMutt, visit: https://neomutt.org
If you find a bug in NeoMutt, please raise an issue at:
    https://github.com/neomutt/neomutt/issues
or send an email to: <neomutt-devel@neomutt.org>

[marvinwankersteen]

Found a solution which works:

set crypt_use_gpgme             = no
set smime_ca_location           = "/etc/ssl/certs/ca-certificates.crt"
set smime_verify_command        = "openssl smime -verify -inform DER -in %s %C -content %f"
set smime_verify_opaque_command = "openssl smime -verify -inform DER -in %s %C"

[jindraj]

@marvinwankersteen: How about importing the certificates authorities into gpgsm database and keep using gpgme instead of legacy smime_*?

gpgsm --import /etc/ssl/certs/ca-certificates.crt

[marvinwankersteen]

Thanks for the hint. I didn't know that you have to import the CAs into gpgsm beforehand. I'm new to neomutt.

The import worked, but the verification is still not possible. Same error.

[rayfordshire]

Yeah, the usage of gpgsm is poorly documented...

If I have to make a guess, I would assume you/gpg does not trust the root certificate. After importing the root certificate in gpgsm you must assign a trust to it (by default it is untrusted, which lets the verification fail). This can be done in different ways, please see section "setting up trust" in https://www.claws-mail.org/faq/index.php/S/MIME_howto on the two ways to do that (automatically via gpg-agent or by editing trustlist.txt)

To rule out that it is a problem with gpgsm itself you can do the following steps to verify an email "by hand" with gpgsm command line:

Verify E-Mail using gpgsm (and openssl)

How to verify a signature of an e-mail using gpgsm on the console
gpgsm cannot handle a MIME mail, thus we must split the e-mail into the signature and the payload/body.

Save the full MIME-Message/E-Mail via neomutt:

<pipe-command>cat > /tmp/signed-mail.eml

Signature

Signature can be saved using neomutt's <save-entry> in the attachment menu most likely the filename smime.p7s.

Alternatively, we can use openssl

openssl cms -cmsout -in signed-mail.eml | sed 1,4d > smime.p7s.base64
openssl cms -cmsout -in signed-mail.eml | sed 1,4d | base64 -d > smime.p7s

The sed deletes the MIME-header.

Payload/Body

The body is a bit trickier as neomutt

a) seems to convert CRLF to LF on *nix, which tampers with the mail.
b) strips the header of the payload MIME part.

To extract the body, we utilise openssl:

openssl cms -verify -in signed-mail.eml > openssl-body

Verifying with gpgsm

gpgsm -n --verify smime.p7s openssl-body
gpgsm -n --verify --assume-base64 smime.p7s.base64 openssl-body

(-n is --dry-run and can be omitted once satisfied)

Appendix

An entry for ~/.gnupg/trustlist.txt looks like:

AA:AA:AA:AA:AA:AA:AA:AA:AA:AA:AA:AA:AA:AA:AA:AA:AA:AA:AA:AA S

where AA... is the Hash of the root certificate in question and the colons can (I think) be omitted.
Note You must reload gpg-agent after editing trustlist.txt in order for the changes to take effect.

gpgconf --reload gpg-agent

[marvinwankersteen]

@rayfordshire: Thank you very much for the instructions and explanation. I have not found this in detail anywhere, not even in the documentation. This should be included, especially for beginners.

Since I basically "have to" trust all CAs, which are all in /etc/ssl/certs/ca-certificates.crt, I have added them all in ~/.gnupg/trustlist.txt.

$ gpgsm --list-keys 2>/dev/null | grep fingerprint | awk '{print $2 " S"}' >> ~/.gnupg/trustlist.txt

The S/MIME-signed mails can then be verified, even without these settings.

I found another hint for debugging gpgsm:

$ cat ~/.gnupg/gpgsm.conf 
log-file /tmp/gpgsm.log
debug 1024
verbose

Perhaps this will help some of you with troubleshooting if this doesn't work.