Script to generate an U2F private key and certificate for OnlyKey

onlykey-u2f-setup.sh

#!/bin/bash

# onlykey-u2f-setup.sh: Helps setting up U2F for OnlyKey.

# Copyright (c) 2016, Jonas Wagner <ltlygwayh@gmail.com>
# All rights reserved.
# 
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions are met:
# 
# 1. Redistributions of source code must retain the above copyright notice, this
#    list of conditions and the following disclaimer.
# 
# 2. Redistributions in binary form must reproduce the above copyright notice,
#    this list of conditions and the following disclaimer in the documentation
#    and/or other materials provided with the distribution.
# 
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
# WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
# DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
# FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
# DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
# SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
# CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.


set -e
set -o pipefail

# Check prerequisites
for command in openssl sed grep tr xxd; do
  if ! which "$command" >/dev/null 2>&1; then
    echo "Could not find command: $command" >&2
    echo "Please install the corresponding package." >&2
    exit 1
  fi
done
for openssl_subcommand in ecparam req x509; do
  if ! openssl list-standard-commands | grep -q "$openssl_subcommand"; then
    echo "OpenSSL does not support the \"$openssl_subcommand\" command." >&2
    echo "Please compile a full-featured version of OpenSSL." >&2
    exit 1
  fi
done

# Create a temporary work directory
workdir="$(mktemp -d)"
trap "rm -rf $workdir" EXIT
cd "$workdir"

# Generate CA key and certificate
openssl ecparam -genkey -name prime256v1 -out ca.key
openssl req -x509 -new -batch -SHA256 -nodes -key ca.key -days 3650 -out ca.crt

# Generate server key
openssl ecparam -genkey -name prime256v1 -out server.key

# Sign the server key with the certificate
openssl req -new -batch -SHA256 -key server.key -nodes -out server.csr
openssl x509 -req -SHA256 -days 3650 -in server.csr -CA ca.crt -CAkey ca.key -CAcreateserial -outform DER -out server.der 2>/dev/null

# Print private key. Extract with openssl, strip initial '00' if needed, and
# verify length.
privkey="$( \
  openssl ec -in server.key -noout -text 2>/dev/null | \
  sed -n '/priv:/,/pub:/p' | grep -o '[0-9a-f]\{2\}' | \
  tr -d ' \n' )"
privkey="${privkey#00}"

if ! echo "$privkey" | grep -q '^[0-9a-f]\{64\}$'; then
  echo "Something went wrong with generating the private key." >&2
  echo "Got this: \"$privkey\"" >&2
  echo "Expected to see a 64-character hex string instead..." >&2
  exit 1
fi

echo "Private Identity:"
echo "$privkey"
echo

# Print certificate
echo "U2F Certificate:"
xxd -p server.der 
echo

# Give users some help
echo "Please enter the values above into the OnlyKey Configuration Wizard."
echo "Also, set up one of the 12 slots to use U2F."
echo
echo "To verify whether this worked, you can perform the following steps:"
echo
echo "- visit https://demo.yubico.com/u2f?tab=register"
echo "- find the \"Register a U2F device\" form"
echo "- enter an arbitrary username and password, and click \"Next\""
echo "- touch your U2F slot"
echo "- the site should say \"Registration completed\""
echo "- click on \"Technical data\""
echo "- check that the attestation certificate shows something similar to:"
echo
openssl x509 -inform DER -in server.der -noout -text