leonklingele

Certificate validation/creation pitfalls

A x509 certificate, and in particular the latest version 3, is the standard for authentication in Public Key Infrastructures (PKIs). Think about Google proving that he's Google before you can communicate with him.

So. Heh. This x509 thing is a tad complicated. Trying to parse such a thing usually end up in the creation of a lot of different vulnerabilities. I won't talk about that here. I will talk about the other complicated thing about them: using them correctly!

So here's a list of pitfalls in the creation of such certificates, but also in the validation and use of them when encountering them in the wild wild web (or in your favorite infrastructure).

KeyUsage
Validity Dates

Encrypting data (Was: AES-CTR with HMAC): Use, in order of preference: (1) The Nacl/libsodium default, (2) Chacha20-Poly1305, or (3) AES-GCM.

You care about this if: you're hiding information from users or the network.

All three options get you "AEAD", which is the only way you want to encrypt in 2015. Options (2) and (3) are morally the same thing: a stream cipher with a polynomial ("thermonuclear CRC") MAC. Option (2) gets there with a native stream cipher and a MAC optimized for general purpose CPUs; Poly1305 is also easier than GCM for library designers to implement safely. Option (3)'s AES-GCM is the industry standard; it's fast and usually hardware accelerated on modern processors, but has implementation safety pitfalls on platforms that aren't accelerated.

Avoid: AES-CBC, AES-CTR by itself, block ciphers with 64-bit blocks --- most especially Blowfish, which is inexplicably popular, OFB mode. Don't ever use RC4, which is comically broken.

Symmetric key length (Was: Use 256 bit keys

	#!/usr/bin/env bash

	set -eufo pipefail

	SUDO=""
	if [ "$EUID" -ne 0 ]; then
	SUDO="sudo"
	if ! [ -x "$(command -v $SUDO)" ]; then
	echo "Error: Running script as non-root and $SUDO is not installed. Exiting." >&2
	exit 1

	[ req ]
	default_bits = 4096
	default_md = sha256
	default_keyfile = private.key
	distinguished_name = req_distinguished_name
	attributes = req_attributes
	x509_extensions = v3_user_req
	req_extensions = v3_user_req

	[ req_distinguished_name ]

	<?php

	$crypto = new Crypt('cbe92e0557602e1bf9c05fffe8e54a809c1bdc5b3c3e2011b9153ce0ce672917', 'ok');

	$enc = $crypto->encrypt('secretmessage');

	// Here we prepend an 'a' -> Decryption should fail, i.e. return false
	// It should NOT trigger an E_ERROR, as we can't handle that.
	$dec = $crypto->decrypt('a' . $enc);

	IP="127.0.0.1"
	PORT="8877"
	SHARED_SECRET="shared secret"

	OPENSSL="/usr/local/opt/libressl/bin/openssl"
	OPENSSL_CMD="$OPENSSL enc -a -A -aes-256-gcm"

	while IFS= read -r MSG; do
	echo "$MSG" \| $OPENSSL_CMD -e -k "$SHARED_SECRET"
	echo

	What we do now:
	We use a static record size of 4K. This gives a good balance of latency and
	throughput.

	Optimize latency:
	By initialy sending small (1 TCP segment) sized records, we are able to avoid
	HoL blocking of the first byte. This means TTFB is sometime lower by a whole
	RTT.

	Optimizing throughput:

	# ..

	# Requires https://st.aticpan.org/source/PERLANCAR/App-nauniq-0.10/script/nauniq
	# SHA256: 046d69b8b1ed74aaff38565f08acc9781e7404fa240b2d091601043a5838f9f0
	# gsed -i 's?#!perl?#!/usr/bin/env perl?' nauniq
	# patch -p1 nauniq < nauniq-ignore-pattern.patch

	__fzf_history__() (
	local line
	shopt -u nocaseglob nocasematch

	From 32a85e260f85fc820fd026637ad38e2230d2887f Mon Sep 17 00:00:00 2001
	From: Leon Klingele <[email protected]>
	Date: Tue, 21 Mar 2017 22:37:56 +0100
	Subject: [PATCH 1/3] 0001-apple-keychain-integration-other-changes.patch

	---
	Makefile.in \| 18 +-
	audit-bsm.c \| 7 +-
	auth-pam.c \| 5 +-
	auth.c \| 2 +-

	- .de-Domain 14 Cent Eine .de-Domain für nur 14 Cent/Monat bei 2 Euro Einrichtungsgebühr
	https://www.netcup.de/bestellen/produkt.php?produkt=1810&hiddenkey=e6a58f069b28d04cd1e332be2684be77
	- .at-Domain 9,90 € pro Jahr! Zu Ostern bekommen Sie eine .at-Domain um 17,5% reduziert - Normalpreis 12€/Jahr!
	https://www.netcup.de/bestellen/produkt.php?produkt=1811&hiddenkey=73d67dbaefe7222f61bf694e5d65e793
	- VPS A Ostern 2017 + Intel Dual-Core + 1 GB DDR3 RAM + 200 GB SATA + Fernwartungskonsole + und vieles mehr Nur 1,44€ / Monat
	https://www.netcup.de/bestellen/produkt.php?produkt=1812&hiddenkey=9a1ef3d6ff803c6cae52bd8be3f36118
	- Root-Server Ostern 2017 + 2 dedizierte Kerne + Intel Xeon E5-2660V3 + 2 GB DDR4 RAM + 4 x 100 GB SAS + RAID10 + und vieles mehr Nur 4,66€ / Monat
	https://www.netcup.de/bestellen/produkt.php?produkt=1813&hiddenkey=552b395c8acb1c4016fc93fd6a3c8f1d
	- RS 4000 SSD 3 Monate kostenlos + 8 dedizierte Kerne + Intel Xeon E5-2680V4 + 24 GB DDR4 RAM + 120 GB SSD + RAID10 + und vieles mehr die ers