#!/bin/bash

usage()
{
cat <<EOF
Usage: $(basename $0) [options]

This shell script is a simple wrapper around the openssl binary. It uses
s_client to get certificate information from remote hosts, or x509 for local
certificate files. It can parse out some of the openssl output or just dump all
of it as text.

Options:

  --all-info   Print all output, including boring things like Modulus and
               Exponent.

  --alt        Print Subject Alternative Names. These will be typically be
               additional hostnames that the certificate is valid for.

  --cn         Print commonName from Subject. This is typically the host for
               which the certificate was issued.

  --debug      Print additional info that might be helpful when debugging this
               script.

  --end        Print certificate expiration date. For additional functionality
               related to certificate expiration, take a look at this script:
               "http://prefetch.net/code/ssl-cert-check".

  --dates      Print start and end dates of when the certificate is valid.

  --file       Use a local certificate file for input.

  --help       Print this help message.

  --host       Fetch the certificate from this remote host.

  --name       Specify a specific domain name (Virtual Host) along with the
               request. This value will be used as the '-servername' in the
               s_client command. This is for TLS SNI (Server Name Indication).

  --issuer     Print the certificate issuer.

  --most-info  Print almost everything. Skip boring things like Modulus and
               Exponent.

  --option     Pass any openssl option through to openssl to get its raw
               output.

  --port       Use this port when conneting to remote host. If ommitted, port
               defaults to 443.

  --subject    Print the certificate Subject -- typically address and org name.

Examples:

  1. Print a list of all hostnames that the certificate used by amazon.com
     is valid for.

     $(basename $0) --host amazon.com --alt
     DNS:uedata.amazon.com
     DNS:amazon.com
     DNS:amzn.com
     DNS:www.amzn.com
     DNS:www.amazon.com

  2. Print issuer of certificate used by smtp.gmail.com. Fetch certficate info
     over port 465.

     $(basename $0) --host smtp.gmail.com --port 465 --issuer
     issuer=
         countryName               = US
         organizationName          = Google Inc
         commonName                = Google Internet Authority G2

  3. Print valid dates for the certificate, using a local file as the source of
     certificate data. Dates are formatted using the date command and display
     time in your local timezone instead of GMT.

     $(basename $0) --file /path/to/file.crt --dates
     valid from: 2014-02-04 16:00:00 PST
     valid till: 2017-02-04 15:59:59 PST


  4. Print certificate serial number. This script doesn't have a special option
     to parse out the serial number, so will use the generic --option flag to
     pass '-serial' through to openssl.

     $(basename $0) --host gmail.com --option -serial
     serial=4BF004B4DDC9C2F8

EOF
}

if ! [ -x "$(type -P openssl)" ]; then
  echo "ERROR: script requires openssl"
  echo "For Debian and friends, get it with 'apt-get install openssl'"
  exit 1
fi

while [ "$1" ]; do
  case "$1" in
        --file)
            shift
            crt="$1"
            source="local"
            ;;
        --host)
            shift
            host="$1"
            source="remote"
            ;;
        --port)
            shift
            port="$1"
            ;;
        --name)
            shift
            servername="-servername $1"
            ;;
        --all-info)
            opt="-text"
            ;;
        --alt)
            FormatOutput() {
              grep -A1 "Subject Alternative Name:" | tail -n1 |
              tr -d ' ' | tr ',' '\n'
              }
            ;;
        --cn)
            opt="-subject -nameopt multiline"
            FormatOutput() {
              awk '/commonName/ {print$NF}'
              }
            ;;
        --dates)
            opt="-dates"
            FormatOutput() {
              dates=$(cat -)
              start=$(grep Before <<<"$dates" | cut -d= -f2-)
              end=$(grep After <<<"$dates" | cut -d= -f2-)
              echo valid from: $(date -d "$start" '+%F %T %Z')
              echo valid till: $(date -d "$end" '+%F %T %Z')
              }
            ;;
        --end)
            opt="-enddate"
            FormatOutput() {
              read end
              end=$(cut -d= -f2- <<<"$end")
              date -d "$end" '+%F %T %Z'
              }
            ;;
        --issuer)
            opt="-issuer -nameopt multiline"
            ;;
        --most-info)
            opt="-text -certopt no_header,no_version,no_serial,no_signame,no_pubkey,no_sigdump,no_aux"
            ;;
        --option)
            shift
            opt="$1"
            ;;
        --subject)
            opt="-subject -nameopt multiline"
            ;;
        --help)
            usage
            exit 0
            ;;
        --debug)
            DEBUG="yes"
            ;;
        *)
            echo "$(basename $0): invalid option $1" >&2
            echo "see --help for usage"
            exit 1
                  ;;
  esac
  shift
done

CheckLocalCert()
{
  openssl x509 -in $crt -noout $opt
}

CheckRemoteCert()
{
  echo |
  openssl s_client $servername -connect $host:$port 2>/dev/null |
  openssl x509 -noout $opt
}

if [ -z "$(type -t FormatOutput)" ]; then
  FormatOutput() { cat; }
fi

if [ -z "$opt" ]; then
  opt="-text -certopt no_header,no_version,no_serial,no_signame,no_pubkey,no_sigdump,no_aux"
fi

if [ -z "$source" ]; then
  echo "ERROR: missing certificate source."
  echo "Provide one via '--file' or '--host' arguments."
  echo "See '--help' for examples."
  exit 1
fi

if [ "$source" == "local" ]; then
  [ -n "$DEBUG" ] && echo "DEBUG: certificate source is local file"
  if [ -z "$crt" ]; then
    echo "ERROR: missing certificate file"
    exit 1
  fi
  [ -n "$DEBUG" ] && echo
  CheckLocalCert | FormatOutput
fi

if [ "$source" == "remote" ]; then
  [ -n "$DEBUG" ] && echo "DEBUG: certificate source is remote host"
  if [ -z "$host" ]; then
    echo "ERROR: missing remote host value."
    echo "Provide one via '--host' argument"
    exit 1
  fi
  if [ -z "$port" ]; then
    [ -n "$DEBUG" ] && echo "DEBUG: defaulting to 443 for port."
    port="443"
  fi
  [ -n "$DEBUG" ] && echo
  CheckRemoteCert | FormatOutput
fi