rsa/util.py

#  Copyright 2011 Sybren A. Stüvel <sybren@stuvel.eu>
#
#  Licensed under the Apache License, Version 2.0 (the "License");
#  you may not use this file except in compliance with the License.
#  You may obtain a copy of the License at
#
#      https://www.apache.org/licenses/LICENSE-2.0
#
#  Unless required by applicable law or agreed to in writing, software
#  distributed under the License is distributed on an "AS IS" BASIS,
#  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
#  See the License for the specific language governing permissions and
#  limitations under the License.

"""Utility functions."""

import sys
from optparse import OptionParser

import rsa.key


def private_to_public() -> None:
    """Reads a private key and outputs the corresponding public key."""

    # Parse the CLI options
    parser = OptionParser(
        usage="usage: %prog [options]",
        description="Reads a private key and outputs the "
        "corresponding public key. Both private and public keys use "
        "the format described in PKCS#1 v1.5",
    )

    parser.add_option(
        "-i",
        "--input",
        dest="infilename",
        type="string",
        help="Input filename. Reads from stdin if not specified",
    )
    parser.add_option(
        "-o",
        "--output",
        dest="outfilename",
        type="string",
        help="Output filename. Writes to stdout of not specified",
    )

    parser.add_option(
        "--inform",
        dest="inform",
        help="key format of input - default PEM",
        choices=("PEM", "DER"),
        default="PEM",
    )

    parser.add_option(
        "--outform",
        dest="outform",
        help="key format of output - default PEM",
        choices=("PEM", "DER"),
        default="PEM",
    )

    (cli, cli_args) = parser.parse_args(sys.argv)

    # Read the input data
    if cli.infilename:
        print(
            "Reading private key from %s in %s format" % (cli.infilename, cli.inform),
            file=sys.stderr,
        )
        with open(cli.infilename, "rb") as infile:
            in_data = infile.read()
    else:
        print("Reading private key from stdin in %s format" % cli.inform, file=sys.stderr)
        in_data = sys.stdin.read().encode("ascii")

    assert type(in_data) == bytes, type(in_data)

    # Take the public fields and create a public key
    priv_key = rsa.key.PrivateKey.load_pkcs1(in_data, cli.inform)
    pub_key = rsa.key.PublicKey(priv_key.n, priv_key.e)

    # Save to the output file
    out_data = pub_key.save_pkcs1(cli.outform)

    if cli.outfilename:
        print(
            "Writing public key to %s in %s format" % (cli.outfilename, cli.outform),
            file=sys.stderr,
        )
        with open(cli.outfilename, "wb") as outfile:
            outfile.write(out_data)
    else:
        print("Writing public key to stdout in %s format" % cli.outform, file=sys.stderr)
        sys.stdout.write(out_data.decode("ascii"))