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diff --git a/contrib/scripts/gnunet-chk.py.in b/contrib/scripts/gnunet-chk.py.in
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+++ b/contrib/scripts/gnunet-chk.py.in
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+#!@PYTHON@
+# This file is part of GNUnet.
+# (C) 2013, 2018 Christian Grothoff (and other contributing authors)
+#
+# GNUnet is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published
+# by the Free Software Foundation; either version 3, or (at your
+# option) any later version.
+#
+# GNUnet is distributed in the hope that it will be useful, but
+# WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+# General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with GNUnet; see the file COPYING.  If not, write to the
+# Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
+# Boston, MA 02110-1301, USA.
+#
+# File:    gnunet-chk.py
+# Brief:   Computes GNUNET style Content Hash Key for a given file
+# Author:  Sree Harsha Totakura
+
+from hashlib import sha512
+import logging
+import os
+import getopt
+import sys
+from Crypto.Cipher import AES
+from functools import reduce
+
+
+# Defaults
+DBLOCK_SIZE = (32 * 1024)   # Data block size
+
+# Pick a multiple of 2 here to achive 8-byte alignment!  We also
+# probably want DBlocks to have (roughly) the same size as IBlocks.
+# With SHA-512, the optimal value is 32768 byte / 128 byte = 256 (128
+# byte = 2 * 512 bits).  DO NOT CHANGE!
+CHK_PER_INODE = 256
+
+CHK_HASH_SIZE = 64              # SHA-512 hash = 512 bits = 64 bytes
+
+CHK_QUERY_SIZE = CHK_HASH_SIZE  # Again a SHA-512 hash
+
+GNUNET_FS_URI_PREFIX = "gnunet://fs/"  # FS CHK URI prefix
+
+GNUNET_FS_URI_CHK_INFIX = "chk/"  # FS CHK URI infix
+
+
+def encode_data_to_string(data):
+    """Returns an ASCII encoding of the given data block like
+    GNUNET_STRINGS_data_to_string() function.
+
+    data: A bytearray representing the block of data which has to be encoded
+    """
+    echart = "0123456789ABCDEFGHIJKLMNOPQRSTUV"
+    assert (None != data)
+    assert (bytearray == type(data))
+    size = len(data)
+    assert (0 != size)
+    vbit = 0
+    wpos = 0
+    rpos = 0
+    bits = 0
+    out = ""
+    while (rpos < size) or (vbit > 0):
+        if (rpos < size) and (vbit < 5):
+            bits = (bits << 8) | data[rpos]  # eat 8 more bits
+            rpos += 1
+            vbit += 8
+        if (vbit < 5):
+            bits <<= (5 - vbit)  # zero-padding
+            assert (vbit == ((size * 8) % 5))
+            vbit = 5
+        out += echart[(bits >> (vbit - 5)) & 31]
+        wpos += 1
+        vbit -= 5
+    assert (0 == vbit)
+    return out
+
+
+def sha512_hash(data):
+    """ Returns the sha512 hash of the given data.
+
+    data: string to hash
+    """
+    hash_obj = sha512()
+    hash_obj.update(data)
+    return hash_obj.digest()
+
+
+class AESKey:
+    """Class for AES Keys. Contains the main key and the initialization
+    vector. """
+
+    key = None                  # The actual AES key
+    iv = None                   # The initialization vector
+    cipher = None               # The cipher object
+    KEY_SIZE = 32               # AES 256-bit key = 32 bytes
+    IV_SIZE = AES.block_size    # Initialization vector size (= AES block size)
+
+    def __init__(self, passphrase):
+        """Creates a new AES key.
+
+        passphrase: string containing the passphrase to get the AES key and
+        initialization vector
+        """
+        passphrase = bytearray(passphrase)
+        self.key = bytearray(self.KEY_SIZE)
+        self.iv = bytearray(self.IV_SIZE)
+        if (len(passphrase) > self.KEY_SIZE):
+            self.key = passphrase[:self.KEY_SIZE]
+            passphrase = passphrase[self.KEY_SIZE:]
+            if (len(passphrase) > self.IV_SIZE):
+                self.iv = passphrase[:self.IV_SIZE]
+            else:
+                self.iv[0:len(passphrase)] = passphrase
+        else:
+            self.key[0:len(passphrase)] = passphrase
+        self.key = str(self.key)
+        self.iv = str(self.iv)
+        assert (len(self.key) == self.KEY_SIZE)
+        assert (len(self.iv) == self.IV_SIZE)
+
+
+def setup_aes_cipher_(aes_key):
+    """Initializes the AES object with settings similar to those in GNUnet.
+
+    aes_key: the AESKey object
+    Returns the newly initialized AES object
+    """
+    return AES.new(aes_key.key, AES.MODE_CFB, aes_key.iv, segment_size=128)
+
+
+def aes_pad_(data):
+    """Adds padding to the data such that the size of the data is a multiple of
+    16 bytes
+
+    data: the data string
+    Returns a tuple:(pad_len, data). pad_len denotes the number of bytes added
+    as padding; data is the new data string with padded bytes at the end
+    """
+    pad_len = len(data) % 16
+    if (0 != pad_len):
+        pad_len = 16 - pad_len
+        pad_bytes = bytearray(15)
+        data += str(pad_bytes[:pad_len])
+    return (pad_len, data)
+
+
+def aes_encrypt(aes_key, data):
+    """Encrypts the given data using AES.
+
+    aes_key: the AESKey object to use for AES encryption
+    data: the data string to encrypt
+    """
+    (pad_len, data) = aes_pad_(data)
+    cipher = setup_aes_cipher_(aes_key)
+    enc_data = cipher.encrypt(data)
+    if (0 != pad_len):
+        enc_data = enc_data[:-pad_len]
+    return enc_data
+
+
+def aes_decrypt(aes_key, data):
+    """Decrypts the given data using AES
+
+    aes_key: the AESKey object to use for AES decryption
+    data: the data string to decrypt
+    """
+    (pad_len, data) = aes_pad_(data)
+    cipher = setup_aes_cipher_(aes_key)
+    ptext = cipher.decrypt(data)
+    if (0 != pad_len):
+        ptext = ptext[:-pad_len]
+    return ptext
+
+
+class Chk:
+    """Class for the content hash key."""
+    key = None
+    query = None
+    fsize = None
+
+    def __init__(self, key, query):
+        assert (len(key) == CHK_HASH_SIZE)
+        assert (len(query) == CHK_QUERY_SIZE)
+        self.key = key
+        self.query = query
+
+    def setSize(self, size):
+        self.fsize = size
+
+    def uri(self):
+        sizestr = repr(self.fsize)
+        if isinstance(self.fsize, int):
+            sizestr = sizestr[:-1]
+        return GNUNET_FS_URI_PREFIX + GNUNET_FS_URI_CHK_INFIX + \
+            encode_data_to_string(bytearray(self.key)) + "." + \
+            encode_data_to_string(bytearray(self.query)) + "." + \
+            sizestr
+
+
+def compute_depth_(size):
+    """Computes the depth of the hash tree.
+
+    size: the size of the file whose tree's depth has to be computed
+    Returns the depth of the tree. Always > 0.
+    """
+    depth = 1
+    fl = DBLOCK_SIZE
+    while (fl < size):
+        depth += 1
+        if ((fl * CHK_PER_INODE) < fl):
+            return depth
+        fl = fl * CHK_PER_INODE
+    return depth
+
+
+def compute_tree_size_(depth):
+    """Calculate how many bytes of payload a block tree of the given depth MAY
+     correspond to at most (this function ignores the fact that some blocks will
+     only be present partially due to the total file size cutting some blocks
+     off at the end).
+
+     depth: depth of the block.  depth==0 is a DBLOCK.
+     Returns the number of bytes of payload a subtree of this depth may
+     correspond to.
+     """
+    rsize = DBLOCK_SIZE
+    for cnt in range(0, depth):
+        rsize *= CHK_PER_INODE
+    return rsize
+
+
+def compute_chk_offset_(depth, end_offset):
+    """Compute the offset of the CHK for the current block in the IBlock
+    above
+
+    depth: depth of the IBlock in the tree (aka overall number of tree levels
+             minus depth); 0 == DBLOCK
+    end_offset: current offset in the overall file, at the *beginning* of the
+                  block for DBLOCK (depth == 0), otherwise at the *end* of the
+                  block (exclusive)
+    Returns the offset in the list of CHKs in the above IBlock
+    """
+    bds = compute_tree_size_(depth)
+    if (depth > 0):
+        end_offset -= 1
+    ret = end_offset / bds
+    return ret % CHK_PER_INODE
+
+
+def compute_iblock_size_(depth, offset):
+    """Compute the size of the current IBLOCK.  The encoder is triggering the
+    calculation of the size of an IBLOCK at the *end* (hence end_offset) of its
+    construction.  The IBLOCK maybe a full or a partial IBLOCK, and this
+    function is to calculate how long it should be.
+
+    depth: depth of the IBlock in the tree, 0 would be a DBLOCK, must be > 0
+             (this function is for IBLOCKs only!)
+    offset: current offset in the payload (!) of the overall file, must be > 0
+              (since this function is called at the end of a block).
+    Returns the number of elements to be in the corresponding IBlock
+    """
+    assert (depth > 0)
+    assert (offset > 0)
+    bds = compute_tree_size_(depth)
+    mod = offset % bds
+    if mod is 0:
+        ret = CHK_PER_INODE
+    else:
+        bds /= CHK_PER_INODE
+        ret = mod / bds
+        if (mod % bds) is not 0:
+            ret += 1
+    return ret
+
+
+def compute_rootchk(readin, size):
+    """Returns the content hash key after generating the hash tree for the given
+    input stream.
+
+    readin: the stream where to read data from
+    size: the size of data to be read
+    """
+    depth = compute_depth_(size)
+    current_depth = 0
+    chks = [None] * (depth * CHK_PER_INODE)  # list buffer
+    read_offset = 0
+    logging.debug("Begining to calculate tree hash with depth: " + repr(depth))
+    while True:
+        if (depth == current_depth):
+            off = CHK_PER_INODE * (depth - 1)
+            assert (chks[off] is not None)
+            logging.debug("Encoding done, reading CHK `" + chks[off].query + \
+                          "' from " + repr(off) + "\n")
+            uri_chk = chks[off]
+            assert (size == read_offset)
+            uri_chk.setSize(size)
+            return uri_chk
+        if (0 == current_depth):
+            pt_size = min(DBLOCK_SIZE, size - read_offset)
+            try:
+                pt_block = readin.read(pt_size)
+            except IOError:
+                logging.warning("Error reading input file stream")
+                return None
+        else:
+            pt_elements = compute_iblock_size_(current_depth, read_offset)
+            pt_block = ""
+            pt_block = \
+                reduce((lambda ba, chk:
+                        ba + (chk.key + chk.query)),
+                       chks[(current_depth - 1) * CHK_PER_INODE:][:pt_elements],
+                       pt_block)
+            pt_size = pt_elements * (CHK_HASH_SIZE + CHK_QUERY_SIZE)
+        assert (len(pt_block) == pt_size)
+        assert (pt_size <= DBLOCK_SIZE)
+        off = compute_chk_offset_(current_depth, read_offset)
+        logging.debug("Encoding data at offset " + repr(read_offset) + \
+                      " and depth " + repr(current_depth) + " with block " \
+                      "size " + repr(pt_size) + " and target CHK offset " + \
+                      repr(current_depth * CHK_PER_INODE))
+        pt_hash = sha512_hash(pt_block)
+        pt_aes_key = AESKey(pt_hash)
+        pt_enc = aes_encrypt(pt_aes_key, pt_block)
+        pt_enc_hash = sha512_hash(pt_enc)
+        chk = Chk(pt_hash, pt_enc_hash)
+        chks[(current_depth * CHK_PER_INODE) + off] = chk
+        if (0 == current_depth):
+            read_offset += pt_size
+            if (read_offset == size) or \
+                    (0 == (read_offset % (CHK_PER_INODE * DBLOCK_SIZE))):
+                current_depth += 1
+        else:
+            if (CHK_PER_INODE == off) or (read_offset == size):
+                current_depth += 1
+            else:
+                current_depth = 0
+
+
+def chkuri_from_path(path):
+    """Returns the CHK URI of the file at the given path.
+
+    path: the path of the file whose CHK has to be calculated
+    """
+    size = os.path.getsize(path)
+    readin = open(path, "rb")
+    chk = compute_rootchk(readin, size)
+    readin.close()
+    return chk.uri()
+
+
+def usage():
+    """Prints help about using this script."""
+    print("""
+Usage: gnunet-chk.py [options] file
+Prints the Content Hash Key of given file in GNUNET-style URI.
+
+Options:
+    -h, --help                : prints this message
+""")
+
+
+if '__main__' == __name__:
+    try:
+        opts, args = getopt.getopt(sys.argv[1:], "h", ["help"])
+    except getopt.GetoptError as err:
+        print(err)
+        print("Exception occured")
+        usage()
+        sys.exit(2)
+    for option, value in opts:
+        if option in("-h", "--help"):
+            usage()
+            sys.exit(0)
+    if len(args) != 1:
+        print("Incorrect number of arguments passed")
+        usage()
+        sys.exit(1)
+    print(chkuri_from_path(args[0]))