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"
    ;;
  *)
    curl "$1" | gpg --import && gpg --verify "$2"
    ;;
  esac
}
error_out(){	# $0 message ...
  echo "$@" 1>&2
  exit 1
}

curl -RO -C - http://ftp.sunet.se/pub/gnu/gmp/gmp-4.1.4.tar.bz2
cat <<EOF > gmp-4.1.4.tar.bz2.asc
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.2.5 (FreeBSD)

iD8DBQBBUekNXW1H39uJn0YRAsITAKCqG1UODqC48AnALpp2Lw7ZkmnIOACbBPJA
1KtUQffxjgTUF3eUJc2IFY4=
=UIYw
-----END PGP SIGNATURE-----
EOF
verify_signature 0xDB899F46 gmp-4.1.4.tar.bz2.asc || error_out "$0: stopped at line $LINENO"

tar xvjf gmp-4.1.4.tar.bz2