python - PyCrypto AES suddenly stops decrypting after several lines of processing input -

i attempting encrypt , decrypt 5-14 mb text files 2 python files, 1 containing encrypt/decrypt methods , being runner methods.

here's class file:

from crypto.cipher import aes crypto import random import sys import codecs reload(sys) sys.setdefaultencoding('utf8') sys.stdout = codecs.getwriter('utf8')(sys.stdout)  class crypt:     def __init__(self, encrypted, key):         self.message = encrypted         self.key = key      def encrypt(self):         iv = random.new().read(aes.block_size)         if len(self.message) % aes.block_size != 0:             self.message += " " * (aes.block_size - (len(self.message) % aes.block_size))          lenkey = len(self.key)         if lenkey > 32:             self.key = self.key[:32]          cipher = aes.new(self.key, aes.mode_cfb, iv)         return iv + cipher.encrypt(self.message)      def decrypt(self):         iv, message = (self.message[:aes.block_size], self.message[aes.block_size:])         if len(message) % aes.block_size != 0:             message += " " * (aes.block_size - (len(message) % aes.block_size))          lenkey = len(self.key)         if lenkey > 32:             self.key = self.key[:32]          cipher = aes.new(self.key, aes.mode_cfb, iv)         return cipher.decrypt(message).strip() 

here's runner:

import crypt_classes crypto.hash import sha256 import sys reload(sys) sys.setdefaultencoding('utf8')  h = sha256.new() while true:     choice = raw_input("encrypt [1] or decrypt [2]? ").strip()     if choice != "1" , choice != "2":         print "invalid choice, please try again."         continue     key = ""     first = ""     confirm = ""     while true:         first = raw_input("enter passphrase (>= 32 chars): ").strip()         # confirm = raw_input("confirm passphrase: ").strip()         confirm = first         if first == confirm , len(confirm) >= 32:             h.update(first)             key = h.hexdigest()             break         else:             print "passphrases did not match or shorter 32 characters. try again."             continue     if choice == "1":         f = open("encrypted.txt", "w")         h = open("source.txt", "r")         message = h.read()         h.close()         encrypter = crypt_classes.crypt(message, key)         e = encrypter.encrypt()         f.write(e)         f.close()         break     elif choice == "2":         f = open("encrypted.txt", "r")         encrypted = f.read()         f.close()         decrypter = crypt_classes.crypt(encrypted, key)         w = open("decrypted.txt", "w")         o = decrypter.decrypt()         w.write(o)         w.close()         break 

encryption works fine, file decrypted , program ostensibly finishes, few lines shown in file along few miscellaneous characters, so:

# data file generated 23andme at: thu may 22 15:47:06 2008 # # below text version of data. fields tab-separated # each line corresponds single snp.  each snp, provide identifier  # (an rsid or internal id), lu� 

no errors thrown, , have no idea why whole file (several mb) isn't decrypting. appreciate help, , please forgive sloppy code or lack of explanation; i'm new here. please comment if further elaboration required.

thank you!

just use simple functions. see no need class here.

taking hex digest , truncating makes effective keylength 128 while seem want 256.

don't write encrypted data utf8. don't use padding cfb mode.

my try (which works on system); can put encrypt , decrypt functions imports in separate file (module), if like.

from crypto.hash import sha256 crypto.cipher import aes crypto import random import sys  def encrypt_data(data, key):     iv=random.new().read(aes.block_size)     aes=aes.new(key, aes.mode_cfb, iv)     return iv+aes.encrypt(data)  def decrypt_data(data, key):     iv = data[:16]     data = data[16:]     aes=aes.new(key, aes.mode_cfb, iv)     return aes.decrypt(data)  h = sha256.new() while true:     choice = raw_input("encrypt [1] or decrypt [2]? ").strip()     if choice != "1" , choice != "2":         print "invalid choice, please try again."         continue     key = ""     first = ""     confirm = ""     while true:         first = raw_input("enter passphrase (>= 32 chars): ").strip()         # confirm = raw_input("confirm passphrase: ").strip()         confirm = first         if first == confirm , len(confirm) >= 32:             h.update(first)             key = h.digest()             break         else:             print "passphrases did not match or shorter 32 characters. try again."             continue     if choice == "1":         f = open("encrypteddna.txt", "w")         h = open("genome_mikolaj_habryn_20080522154706.txt", "r")         message = h.read()        h.close()        encmessage = encrypt_data(message, key)        f.write(encmessage)        f.close()        break     elif choice == "2":         f = open("encrypteddna.txt", "r")         encrypted = f.read()         f.close()         decrypted = decrypt_data(encrypted,key)         w = open("decrypteddna.txt", "w")         w.write(decrypted)         w.close()         break 

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