pycryptodome/lib/Crypto/IO/PKCS8.py

#
#  PublicKey/PKCS8.py : PKCS#8 functions
#
# ===================================================================
#
# Copyright (c) 2014, Legrandin <helderijs@gmail.com>
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"""
Module for handling private keys wrapped according to `PKCS#8`_.

PKCS8 is a standard for storing and transferring private key information.
The wrapped key can either be clear or encrypted.

All encryption algorithms are based on passphrase-based key derivation.
The following mechanisms are fully supported:

* *PBKDF2WithHMAC-SHA1AndAES128-CBC*
* *PBKDF2WithHMAC-SHA1AndAES192-CBC*
* *PBKDF2WithHMAC-SHA1AndAES256-CBC*
* *PBKDF2WithHMAC-SHA1AndDES-EDE3-CBC*
* *scryptAndAES128-CBC*
* *scryptAndAES192-CBC*
* *scryptAndAES256-CBC*

The following mechanisms are only supported for importing keys.
They are much weaker than the ones listed above, and they are provided
for backward compatibility only:

* *pbeWithMD5AndRC2-CBC*
* *pbeWithMD5AndDES-CBC*
* *pbeWithSHA1AndRC2-CBC*
* *pbeWithSHA1AndDES-CBC*

.. _`PKCS#8`: http://www.ietf.org/rfc/rfc5208.txt

"""

from Crypto.Util.py3compat import *

from Crypto.Util.asn1 import (
            DerNull,
            DerSequence,
            newDerSequence,
            DerObjectId,
            DerOctetString,
            newDerOctetString,
            )

from Crypto.IO._PBES import PBES1, PBES2

__all__ = ['wrap', 'unwrap']


def decode_der(obj_class, binstr):
    """Instantiate a DER object class, decode a DER binary string in it, and
    return the object."""
    der = obj_class()
    der.decode(binstr)
    return der


def wrap(private_key, key_oid, passphrase=None, protection=None,
         prot_params=None, key_params=None, randfunc=None):
    """Wrap a private key into a PKCS#8 blob (clear or encrypted).

    :Parameters:

      private_key : byte string
        The private key encoded in binary form. The actual encoding is
        algorithm specific. In most cases, it is DER.

      key_oid : string
        The object identifier (OID) of the private key to wrap.
        It is a dotted string, like "``1.2.840.113549.1.1.1``" (for RSA keys).

      passphrase : (binary) string
        The secret passphrase from which the wrapping key is derived.
        Set it only if encryption is required.

      protection : string
        The identifier of the algorithm to use for securely wrapping the key.
        The default value is '``PBKDF2WithHMAC-SHA1AndDES-EDE3-CBC``'.

      prot_params : dictionary
        Parameters for the protection algorithm.

        +------------------+-----------------------------------------------+
        | Key              | Description                                   |
        +==================+===============================================+
        | iteration_count  | The KDF algorithm is repeated several times to|
        |                  | slow down brute force attacks on passwords    |
        |                  | (called *N* or CPU/memory cost in scrypt).    |
        |                  |                                               |
        |                  | The default value for PBKDF2 is 1 000.        |
        |                  | The default value for scrypt is 16 384.       |
        +------------------+-----------------------------------------------+
        | salt_size        | Salt is used to thwart dictionary and rainbow |
        |                  | attacks on passwords. The default value is 8  |
        |                  | bytes.                                        |
        +------------------+-----------------------------------------------+
        | block_size       | *(scrypt only)* Memory-cost (r). The default  |
        |                  | value is 8.                                   |
        +------------------+-----------------------------------------------+
        | parallelization  | *(scrypt only)* CPU-cost (p). The default     |
        |                  | value is 1.                                   |
        +------------------+-----------------------------------------------+

      key_params : DER object
        The algorithm parameters associated to the private key.
        It is required for algorithms like DSA, but not for others like RSA.

      randfunc : callable
        Random number generation function; it should accept a single integer
        N and return a string of random data, N bytes long.
        If not specified, a new RNG will be instantiated
        from ``Crypto.Random``.

    :Return:
      The PKCS#8-wrapped private key (possibly encrypted),
      as a binary string.
    """

    if key_params is None:
        key_params = DerNull()

    #
    #   PrivateKeyInfo ::= SEQUENCE {
    #       version                 Version,
    #       privateKeyAlgorithm     PrivateKeyAlgorithmIdentifier,
    #       privateKey              PrivateKey,
    #       attributes              [0]  IMPLICIT Attributes OPTIONAL
    #   }
    #
    pk_info = newDerSequence(
                0,
                newDerSequence(
                    DerObjectId(key_oid),
                    key_params
                ),
                newDerOctetString(private_key)
            )
    pk_info_der = pk_info.encode()

    if not passphrase:
        return pk_info_der

    # Encryption with PBES2
    passphrase = tobytes(passphrase)
    if protection is None:
        protection = 'PBKDF2WithHMAC-SHA1AndDES-EDE3-CBC'
    return PBES2.encrypt(pk_info_der, passphrase,
                         protection, prot_params, randfunc)


def unwrap(p8_private_key, passphrase=None):
    """Unwrap a private key from a PKCS#8 blob (clear or encrypted).

    :Parameters:
      p8_private_key : byte string
        The private key wrapped into a PKCS#8 blob
      passphrase : (byte) string
        The passphrase to use to decrypt the blob (if it is encrypted).
    :Return:
      A tuple containing:

      #. the algorithm identifier of the wrapped key (OID, dotted string)
      #. the private key (byte string, DER encoded)
      #. the associated parameters (byte string, DER encoded) or ``None``

    :Raises ValueError:
      If decoding fails
    """

    if passphrase:
        passphrase = tobytes(passphrase)
        found = False
        for pbes in PBES1, PBES2:
            try:
                p8_private_key = pbes.decrypt(p8_private_key, passphrase)
            except ValueError:
                pass
            else:
                found = True
                break
        if not found:
            raise ValueError("Unsupported PKCS#5 Object ID ")

    pk_info = decode_der(DerSequence, p8_private_key)
    if len(pk_info) == 2 and not passphrase:
        raise ValueError("Not a valid clear PKCS#8 structure "
                         "(maybe it is encrypted?)")
    if not 3 <= len(pk_info) <= 4 or pk_info[0] != 0:
        raise ValueError("Not a valid PrivateKeyInfo SEQUENCE")

    #
    #   AlgorithmIdentifier  ::=  SEQUENCE  {
    #       algorithm               OBJECT IDENTIFIER,
    #       parameters              ANY DEFINED BY algorithm OPTIONAL
    #   }
    #
    algo_id = decode_der(DerSequence, pk_info[1])
    if not 1 <= len(algo_id) <= 2:
        raise ValueError("Not a valid AlgorithmIdentifier SEQUENCE")
    algo = decode_der(DerObjectId, algo_id[0]).value
    private_key = decode_der(DerOctetString, pk_info[2]).payload
    if len(algo_id) == 2 and algo_id[1] != b('\x05\x00'):
        params = algo_id[1]
    else:
        params = None
    return (algo, private_key, params)