verify_digest(){	# $0 method file string
  case "$1" in
  *)
    DIGEST=`echo "$1" | tr a-z A-Z`
    [ "$DIGEST($2)= $3" = "`openssl $1 $2`" ]
    ;;
  esac
}
verify_signature(){	# $0 [url|id] sig
  case "$1" in
  0x*)
    gpg --recv-keys "$1" && gpg --verify "$2"
    ;;
  http:*|ftp:*)
    curl "$1" | gpg --import && gpg --verify "$2"
    ;;
  *)
    gpg --import && gpg --verify "$1"
    ;;
  esac
}
error_out(){	# $0 message ...
  echo "$@" 1>&2
  exit 1
}

wget -N ftp://core.ring.gr.jp/pub/GNU/gnu-arch/tla-1.3.4.tar.gz
wget -N ftp://core.ring.gr.jp/pub/GNU/gnu-arch/tla-1.3.4.tar.gz.sig
verify_signature http://www.atai.org/public_key.txt tla-1.3.4.tar.gz.sig || error_out "$0: stopped at line $LINENO"
tar xvzf tla-1.3.4.tar.gz