There are more flags than the help output indicate.
decrypt -k, --private-key-filename File containing the base64 encoded private key
decrypt -o, --output-format <format> Output format of matched data [default: utf8-lossy] [possible values: raw, utf8-lossy]
generate-key-pair -o, --output-format <format> Output format of key pair [default: json] [possible values: json]