Contract con_rsa_encryption
| Creator | ae9cfa894495930b8d2f1707ab936325b5c848ace677bb8ba41dfe7dcdb3e3e6 |
| Creation Hash | 6bb4e5493401b6fafc8958cb9ab2a443d9f82aa5f5d9c6ca250f783c13ce151f |
| Created On | 880 days ago - 12/6/2021, 12:01:15 AM UTC+0 |
Contract Code
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random.seed()
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@construct
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def seed():
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pass
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def assert_int(var: int, name: str) -> None:
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assert isinstance(var, int), "%s should be an integer, not %s" % (name, type(var))
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def encrypt_int(message: int, ekey: int, n: int) -> int:
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"""Encrypts a message using encryption key 'ekey', working modulo n"""
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assert_int(message, "message")
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assert_int(ekey, "ekey")
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assert_int(n, "n")
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assert message >= 0, "Only non-negative numbers are supported"
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assert message <= n, "The message %i is too long for n=%i" % (message, n)
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return pow(message, ekey, n)
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def bytes2int(raw_bytes: bytes) -> int:
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r"""Converts a list of bytes or an 8-bit string to an integer.
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When using unicode strings, encode it to some encoding like UTF8 first.
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>>> (((128 * 256) + 64) * 256) + 15
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8405007
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>>> bytes2int(b'\x80@\x0f')
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8405007
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"""
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return int.from_bytes(raw_bytes, "big", signed=False)
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def div_ceil(a: int, b: int) -> int:
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return a//b + bool(a%b)
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def int2bytes(number: int, fill_size: int = 0) -> bytes:
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"""
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Convert an unsigned integer to bytes (big-endian)::
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Does not preserve leading zeros if you don't specify a fill size.
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:param number:
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Integer value
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:param fill_size:
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If the optional fill size is given the length of the resulting
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byte string is expected to be the fill size and will be padded
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with prefix zero bytes to satisfy that length.
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:returns:
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Raw bytes (base-256 representation).
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:raises:
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``OverflowError`` when fill_size is given and the number takes up more
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bytes than fit into the block. This requires the ``overflow``
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argument to this function to be set to ``False`` otherwise, no
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error will be raised.
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"""
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assert number >= 0, "Number must be an unsigned integer: %d" % number
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bytes_required = max(1, div_ceil(number.bit_length(), 8))
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if fill_size > 0:
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return number.to_bytes(fill_size, "big")
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return number.to_bytes(bytes_required, "big")
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def bit_size(num: int) -> int:
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"""
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Number of bits needed to represent a integer excluding any prefix
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0 bits.
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Usage::
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>>> bit_size(1023)
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10
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>>> bit_size(1024)
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11
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>>> bit_size(1025)
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:param num:
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Integer value. If num is 0, returns 0. Only the absolute value of the
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number is considered. Therefore, signed integers will be abs(num)
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before the number's bit length is determined.
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:returns:
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Returns the number of bits in the integer.
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"""
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assert isinstance(num, int), "bit_size(num) only supports integers, not %r" % type(num)
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return num.bit_length()
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def byte_size(number: int) -> int:
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"""
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Returns the number of bytes required to hold a specific long number.
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The number of bytes is rounded up.
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Usage::
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>>> byte_size(1 << 1023)
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128
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>>> byte_size((1 << 1024) - 1)
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128
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>>> byte_size(1 << 1024)
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:param number:
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An unsigned integer
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:returns:
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The number of bytes required to hold a specific long number.
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"""
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if number == 0:
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return 1
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return div_ceil(bit_size(number), 8)
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def pad_for_encryption(message: bytes, target_length: int) -> bytes:
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r"""Pads the message for encryption, returning the padded message.
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:return: 00 02 RANDOM_DATA 00 MESSAGE
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>>> block = pad_for_encryption(b'hello', 16)
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>>> len(block)
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16
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>>> block[0:2]
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b'\x00\x02'
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>>> block[-6:]
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b'\x00hello'
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"""
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max_msglength = target_length - 11
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msglength = len(message)
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assert msglength <= max_msglength, "%i bytes needed for message, but there is only space for %i" % (msglength, max_msglength)
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# Get random padding
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padding = b""
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padding_length = target_length - msglength - 3
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# We remove 0-bytes, so we'll end up with less padding than we've asked for,
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# so keep adding data until we're at the correct length.
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while len(padding) < padding_length:
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needed_bytes = padding_length - len(padding)
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# Always read at least 8 bytes more than we need, and trim off the rest
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# after removing the 0-bytes. This increases the chance of getting
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# enough bytes, especially when needed_bytes is small
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random_bits = random.getrandbits((needed_bytes + 5) * 8)
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new_padding = int2bytes(random_bits, fill_size=needed_bytes+5)
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new_padding = new_padding.replace(b"\x00", b"")
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padding = padding + new_padding[:needed_bytes]
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assert len(padding) == padding_length, "Invalid padding length: %i != %i" % (len(padding), padding_length)
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return b"".join([b"\x00\x02", padding, b"\x00", message])
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@export
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def encrypt(message_str: str, n: int, e: int) -> str:
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"""Encrypts the given message using PKCS#1 v1.5
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:param message: the message to encrypt. Must be a byte string no longer than
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``k-11`` bytes, where ``k`` is the number of bytes needed to encode
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the ``n`` component of the public key.
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:param pub_key: the :py:class:`rsa.PublicKey` to encrypt with.
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:raise OverflowError: when the message is too large to fit in the padded
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block.
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>>> from rsa import key, common
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>>> (pub_key, priv_key) = key.newkeys(256)
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>>> message = b'hello'
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>>> crypto = encrypt(message, pub_key)
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The crypto text should be just as long as the public key 'n' component:
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>>> len(crypto) == common.byte_size(pub_key.n)
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True
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"""
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message = message_str.encode()
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keylength = byte_size(n)
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padded = pad_for_encryption(message, keylength)
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payload = bytes2int(padded)
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encrypted = encrypt_int(payload, e, n)
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block = int2bytes(encrypted, keylength)
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return block.hex()
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Byte Code
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