Copy gVisor public key and a helper script in container helpers

Download and copy the following artifacts that will be used for building
a Debian-based Dangerzone container image in the subsequent commits:
* The APT key for the gVisor repo [1]
* A helper script for building reproducible Debian images [2]

[1] https://gvisor.dev/archive.key
[2] https://github.com/reproducible-containers/repro-sources-list.sh/blob/d15cf12b26395b857b24fba223b108aff1c91b26/repro-sources-list.sh

THIRD_PARTY_NOTICE

@@ -0,0 +1,14 @@
+This project includes third-party components as follows:
+
+1. gVisor APT Key
+   - URL: https://gvisor.dev/archive.key
+   - Last updated: 2025-01-21
+   - Description: This is the public key used for verifying packages from the gVisor repository.
+
+2. Reproducible Containers Helper Script
+   - URL: https://github.com/reproducible-containers/repro-sources-list.sh/blob/d15cf12b26395b857b24fba223b108aff1c91b26/repro-sources-list.sh
+   - Last updated: 2025-01-21
+   - Description: This script is used for building reproducible Debian images.
+
+Please refer to the respective sources for licensing information and further details regarding the use of these components.
+

dangerzone/container_helpers/gvisor.key

@@ -0,0 +1,29 @@
+-----BEGIN PGP PUBLIC KEY BLOCK-----
+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+EwEKADgCGwMFCwkIBwIGFQoJCAsCBBYCAwECHgECF4AWIQRvHfheOnHCSRjnJ9Vv
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+EQfk7RHJSLMJXAnNDH7OUDgrirSssg/dlQ5uAHA9Au80VvC5fsTKza8b3Aydw3SV
+iB8/Yuikbl8wKbpSGiXtR4viElXjNips0+mBqaUk2xpqSBrsfN+FezcInVXaXFeq
+xtpq2/3M3DYbqCRjqeyd9wNi92FHdOusNrK4MYe0pAYbGjc65BwH+F0T4oJ8ZSJV
+lIt+FZ0MqM1T97XadybYFsJh8qvajQpZEPL+zzNncc4f1d80e7+lwIZV/al0FZWW
+Zlp7TpbeO/uW+lHs5W14YKwaQVh1whapKXTrATipNOOSCw2hnfrT8V7Hy55QWaGZ
+f4/kfy929EeCP16d/LqOClv0j0RBr6NhRBQ0l/BE/mXjJwIk6nKwi+Yi4ek1ARi6
+AlCMLn9AZF7aTGpvCiftzIrlyDfVZT5IX03TayxRHZ4b1Rj8eyJaHcjI49u83gkr
+4LGX08lEawn9nxFSx4RCg2swGiYw5F436wwwAIozqJuDASeTa3QND3au5v0oYWnl
+umDySUl5wPaAaALgzA==
+=5/8T
+-----END PGP PUBLIC KEY BLOCK-----

dangerzone/container_helpers/repro-sources-list.sh

@@ -0,0 +1,103 @@
+#!/bin/bash
+#
+#   Copyright The repro-sources-list.sh Authors.
+#
+#   Licensed under the Apache License, Version 2.0 (the "License");
+#   you may not use this file except in compliance with the License.
+#   You may obtain a copy of the License at
+#
+#       http://www.apache.org/licenses/LICENSE-2.0
+#
+#   Unless required by applicable law or agreed to in writing, software
+#   distributed under the License is distributed on an "AS IS" BASIS,
+#   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#   See the License for the specific language governing permissions and
+#   limitations under the License.
+
+# -----------------------------------------------------------------------------
+# repro-sources-list.sh:
+# configures /etc/apt/sources.list and similar files for installing packages from a snapshot.
+#
+# This script is expected to be executed inside Dockerfile.
+#
+# The following distributions are supported:
+# - debian:11    (/etc/apt/sources.list)
+# - debian:12    (/etc/apt/sources.list.d/debian.sources)
+# - ubuntu:22.04 (/etc/apt/sources.list)
+# - ubuntu:24.04 (/etc/apt/sources.listd/ubuntu.sources)
+# - archlinux    (/etc/pacman.d/mirrorlist)
+#
+# For the further information, see https://github.com/reproducible-containers/repro-sources-list.sh
+# -----------------------------------------------------------------------------
+
+set -eux -o pipefail
+
+. /etc/os-release
+
+: "${KEEP_CACHE:=1}"
+
+keep_apt_cache() {
+	rm -f /etc/apt/apt.conf.d/docker-clean
+	echo 'Binary::apt::APT::Keep-Downloaded-Packages "true";' >/etc/apt/apt.conf.d/keep-cache
+}
+
+case "${ID}" in
+"debian")
+	: "${SNAPSHOT_ARCHIVE_BASE:=http://snapshot.debian.org/archive/}"
+	: "${BACKPORTS:=}"
+	if [ -e /etc/apt/sources.list.d/debian.sources ]; then
+		: "${SOURCE_DATE_EPOCH:=$(stat --format=%Y /etc/apt/sources.list.d/debian.sources)}"
+		rm -f /etc/apt/sources.list.d/debian.sources
+	else
+		: "${SOURCE_DATE_EPOCH:=$(stat --format=%Y /etc/apt/sources.list)}"
+	fi
+	snapshot="$(printf "%(%Y%m%dT%H%M%SZ)T\n" "${SOURCE_DATE_EPOCH}")"
+	# TODO: use the new format for Debian >= 12
+	echo "deb [check-valid-until=no] ${SNAPSHOT_ARCHIVE_BASE}debian/${snapshot} ${VERSION_CODENAME} main" >/etc/apt/sources.list
+	echo "deb [check-valid-until=no] ${SNAPSHOT_ARCHIVE_BASE}debian-security/${snapshot} ${VERSION_CODENAME}-security main" >>/etc/apt/sources.list
+	echo "deb [check-valid-until=no] ${SNAPSHOT_ARCHIVE_BASE}debian/${snapshot} ${VERSION_CODENAME}-updates main" >>/etc/apt/sources.list
+	if [ "${BACKPORTS}" = 1 ]; then echo "deb [check-valid-until=no] ${SNAPSHOT_ARCHIVE_BASE}debian/${snapshot} ${VERSION_CODENAME}-backports main" >>/etc/apt/sources.list; fi
+	if [ "${KEEP_CACHE}" = 1 ]; then keep_apt_cache; fi
+	;;
+"ubuntu")
+	: "${SNAPSHOT_ARCHIVE_BASE:=http://snapshot.ubuntu.com/}"
+	if [ -e /etc/apt/sources.list.d/ubuntu.sources ]; then
+		: "${SOURCE_DATE_EPOCH:=$(stat --format=%Y /etc/apt/sources.list.d/ubuntu.sources)}"
+		rm -f /etc/apt/sources.list.d/ubuntu.sources
+	else
+		: "${SOURCE_DATE_EPOCH:=$(stat --format=%Y /etc/apt/sources.list)}"
+	fi
+	snapshot="$(printf "%(%Y%m%dT%H%M%SZ)T\n" "${SOURCE_DATE_EPOCH}")"
+	# TODO: use the new format for Ubuntu >= 24.04
+	echo "deb [check-valid-until=no] ${SNAPSHOT_ARCHIVE_BASE}ubuntu/${snapshot} ${VERSION_CODENAME} main restricted" >/etc/apt/sources.list
+	echo "deb [check-valid-until=no] ${SNAPSHOT_ARCHIVE_BASE}ubuntu/${snapshot} ${VERSION_CODENAME}-updates main restricted" >>/etc/apt/sources.list
+	echo "deb [check-valid-until=no] ${SNAPSHOT_ARCHIVE_BASE}ubuntu/${snapshot} ${VERSION_CODENAME} universe" >>/etc/apt/sources.list
+	echo "deb [check-valid-until=no] ${SNAPSHOT_ARCHIVE_BASE}ubuntu/${snapshot} ${VERSION_CODENAME}-updates universe" >>/etc/apt/sources.list
+	echo "deb [check-valid-until=no] ${SNAPSHOT_ARCHIVE_BASE}ubuntu/${snapshot} ${VERSION_CODENAME} multiverse" >>/etc/apt/sources.list
+	echo "deb [check-valid-until=no] ${SNAPSHOT_ARCHIVE_BASE}ubuntu/${snapshot} ${VERSION_CODENAME}-updates multiverse" >>/etc/apt/sources.list
+	echo "deb [check-valid-until=no] ${SNAPSHOT_ARCHIVE_BASE}ubuntu/${snapshot} ${VERSION_CODENAME}-backports main restricted universe multiverse" >>/etc/apt/sources.list
+	echo "deb [check-valid-until=no] ${SNAPSHOT_ARCHIVE_BASE}ubuntu/${snapshot} ${VERSION_CODENAME}-security main restricted" >>/etc/apt/sources.list
+	echo "deb [check-valid-until=no] ${SNAPSHOT_ARCHIVE_BASE}ubuntu/${snapshot} ${VERSION_CODENAME}-security universe" >>/etc/apt/sources.list
+	echo "deb [check-valid-until=no] ${SNAPSHOT_ARCHIVE_BASE}ubuntu/${snapshot} ${VERSION_CODENAME}-security multiverse" >>/etc/apt/sources.list
+	if [ "${KEEP_CACHE}" = 1 ]; then keep_apt_cache; fi
+	# http://snapshot.ubuntu.com is redirected to https, so we have to install ca-certificates
+	export DEBIAN_FRONTEND=noninteractive
+	apt-get -o Acquire::https::Verify-Peer=false update >&2
+	apt-get -o Acquire::https::Verify-Peer=false install -y ca-certificates >&2
+	;;
+"arch")
+	: "${SNAPSHOT_ARCHIVE_BASE:=http://archive.archlinux.org/}"
+	: "${SOURCE_DATE_EPOCH:=$(stat --format=%Y /var/log/pacman.log)}"
+	export SOURCE_DATE_EPOCH
+	# shellcheck disable=SC2016
+	date -d "@${SOURCE_DATE_EPOCH}" "+Server = ${SNAPSHOT_ARCHIVE_BASE}repos/%Y/%m/%d/\$repo/os/\$arch" >/etc/pacman.d/mirrorlist
+	;;
+*)
+	echo >&2 "Unsupported distribution: ${ID}"
+	exit 1
+	;;
+esac
+
+: "${WRITE_SOURCE_DATE_EPOCH:=/dev/null}"
+echo "${SOURCE_DATE_EPOCH}" >"${WRITE_SOURCE_DATE_EPOCH}"
+echo "SOURCE_DATE_EPOCH=${SOURCE_DATE_EPOCH}"