问题
OpenSSL provides a popular (but insecure – see below!) command line interface for AES encryption:
openssl aes-256-cbc -salt -in filename -out filename.enc
Python has support for AES in the shape of the PyCrypto package, but it only provides the tools. How to use Python/PyCrypto to decrypt files that have been encrypted using OpenSSL?
Notice
This question used to also concern encryption in Python using the same scheme. I have since removed that part to discourage anyone from using it. Do NOT encrypt any more data in this way, because it is NOT secure by today\'s standards. You should ONLY use decryption, for no other reasons than BACKWARD COMPATIBILITY, i.e. when you have no other choice. Want to encrypt? Use NaCl/libsodium if you possibly can.
回答1:
Given the popularity of Python, at first I was disappointed that there was no complete answer to this question to be found. It took me a fair amount of reading different answers on this board, as well as other resources, to get it right. I thought I might share the result for future reference and perhaps review; I'm by no means a cryptography expert! However, the code below appears to work seamlessly:
from hashlib import md5
from Crypto.Cipher import AES
from Crypto import Random
def derive_key_and_iv(password, salt, key_length, iv_length):
d = d_i = ''
while len(d) < key_length + iv_length:
d_i = md5(d_i + password + salt).digest()
d += d_i
return d[:key_length], d[key_length:key_length+iv_length]
def decrypt(in_file, out_file, password, key_length=32):
bs = AES.block_size
salt = in_file.read(bs)[len('Salted__'):]
key, iv = derive_key_and_iv(password, salt, key_length, bs)
cipher = AES.new(key, AES.MODE_CBC, iv)
next_chunk = ''
finished = False
while not finished:
chunk, next_chunk = next_chunk, cipher.decrypt(in_file.read(1024 * bs))
if len(next_chunk) == 0:
padding_length = ord(chunk[-1])
chunk = chunk[:-padding_length]
finished = True
out_file.write(chunk)
Usage:
with open(in_filename, 'rb') as in_file, open(out_filename, 'wb') as out_file:
decrypt(in_file, out_file, password)
If you see a chance to improve on this or extend it to be more flexible (e.g. make it work without salt, or provide Python 3 compatibility), please feel free to do so.
Notice
This answer used to also concern encryption in Python using the same scheme. I have since removed that part to discourage anyone from using it. Do NOT encrypt any more data in this way, because it is NOT secure by today's standards. You should ONLY use decryption, for no other reasons than BACKWARD COMPATIBILITY, i.e. when you have no other choice. Want to encrypt? Use NaCl/libsodium if you possibly can.
回答2:
I am re-posting your code with a couple of corrections (I didn't want to obscure your version). While your code works, it does not detect some errors around padding. In particular, if the decryption key provided is incorrect, your padding logic may do something odd. If you agree with my change, you may update your solution.
from hashlib import md5
from Crypto.Cipher import AES
from Crypto import Random
def derive_key_and_iv(password, salt, key_length, iv_length):
d = d_i = ''
while len(d) < key_length + iv_length:
d_i = md5(d_i + password + salt).digest()
d += d_i
return d[:key_length], d[key_length:key_length+iv_length]
# This encryption mode is no longer secure by today's standards.
# See note in original question above.
def obsolete_encrypt(in_file, out_file, password, key_length=32):
bs = AES.block_size
salt = Random.new().read(bs - len('Salted__'))
key, iv = derive_key_and_iv(password, salt, key_length, bs)
cipher = AES.new(key, AES.MODE_CBC, iv)
out_file.write('Salted__' + salt)
finished = False
while not finished:
chunk = in_file.read(1024 * bs)
if len(chunk) == 0 or len(chunk) % bs != 0:
padding_length = bs - (len(chunk) % bs)
chunk += padding_length * chr(padding_length)
finished = True
out_file.write(cipher.encrypt(chunk))
def decrypt(in_file, out_file, password, key_length=32):
bs = AES.block_size
salt = in_file.read(bs)[len('Salted__'):]
key, iv = derive_key_and_iv(password, salt, key_length, bs)
cipher = AES.new(key, AES.MODE_CBC, iv)
next_chunk = ''
finished = False
while not finished:
chunk, next_chunk = next_chunk, cipher.decrypt(in_file.read(1024 * bs))
if len(next_chunk) == 0:
padding_length = ord(chunk[-1])
if padding_length < 1 or padding_length > bs:
raise ValueError("bad decrypt pad (%d)" % padding_length)
# all the pad-bytes must be the same
if chunk[-padding_length:] != (padding_length * chr(padding_length)):
# this is similar to the bad decrypt:evp_enc.c from openssl program
raise ValueError("bad decrypt")
chunk = chunk[:-padding_length]
finished = True
out_file.write(chunk)
回答3:
The code below should be Python 3 compatible with the small changes documented in the code. Also wanted to use os.urandom instead of Crypto.Random. 'Salted__' is replaced with salt_header that can be tailored or left empty if needed.
from os import urandom
from hashlib import md5
from Crypto.Cipher import AES
def derive_key_and_iv(password, salt, key_length, iv_length):
d = d_i = b'' # changed '' to b''
while len(d) < key_length + iv_length:
# changed password to str.encode(password)
d_i = md5(d_i + str.encode(password) + salt).digest()
d += d_i
return d[:key_length], d[key_length:key_length+iv_length]
def encrypt(in_file, out_file, password, salt_header='', key_length=32):
# added salt_header=''
bs = AES.block_size
# replaced Crypt.Random with os.urandom
salt = urandom(bs - len(salt_header))
key, iv = derive_key_and_iv(password, salt, key_length, bs)
cipher = AES.new(key, AES.MODE_CBC, iv)
# changed 'Salted__' to str.encode(salt_header)
out_file.write(str.encode(salt_header) + salt)
finished = False
while not finished:
chunk = in_file.read(1024 * bs)
if len(chunk) == 0 or len(chunk) % bs != 0:
padding_length = (bs - len(chunk) % bs) or bs
# changed right side to str.encode(...)
chunk += str.encode(
padding_length * chr(padding_length))
finished = True
out_file.write(cipher.encrypt(chunk))
def decrypt(in_file, out_file, password, salt_header='', key_length=32):
# added salt_header=''
bs = AES.block_size
# changed 'Salted__' to salt_header
salt = in_file.read(bs)[len(salt_header):]
key, iv = derive_key_and_iv(password, salt, key_length, bs)
cipher = AES.new(key, AES.MODE_CBC, iv)
next_chunk = ''
finished = False
while not finished:
chunk, next_chunk = next_chunk, cipher.decrypt(
in_file.read(1024 * bs))
if len(next_chunk) == 0:
padding_length = chunk[-1] # removed ord(...) as unnecessary
chunk = chunk[:-padding_length]
finished = True
out_file.write(bytes(x for x in chunk)) # changed chunk to bytes(...)
回答4:
I know this is a bit late but here is a solution that I blogged in 2013 about how to use the python pycrypto package to encrypt/decrypt in an openssl compatible way. It has been tested on python2.7 and python3.x. The source code and a test script can be found here.
One of the key differences between this solution and the excellent solutions presented above is that it differentiates between pipe and file I/O which can cause problems in some applications.
The key functions from that blog are shown below.
# ================================================================
# get_key_and_iv
# ================================================================
def get_key_and_iv(password, salt, klen=32, ilen=16, msgdgst='md5'):
'''
Derive the key and the IV from the given password and salt.
This is a niftier implementation than my direct transliteration of
the C++ code although I modified to support different digests.
CITATION: http://stackoverflow.com/questions/13907841/implement-openssl-aes-encryption-in-python
@param password The password to use as the seed.
@param salt The salt.
@param klen The key length.
@param ilen The initialization vector length.
@param msgdgst The message digest algorithm to use.
'''
# equivalent to:
# from hashlib import <mdi> as mdf
# from hashlib import md5 as mdf
# from hashlib import sha512 as mdf
mdf = getattr(__import__('hashlib', fromlist=[msgdgst]), msgdgst)
password = password.encode('ascii', 'ignore') # convert to ASCII
try:
maxlen = klen + ilen
keyiv = mdf(password + salt).digest()
tmp = [keyiv]
while len(tmp) < maxlen:
tmp.append( mdf(tmp[-1] + password + salt).digest() )
keyiv += tmp[-1] # append the last byte
key = keyiv[:klen]
iv = keyiv[klen:klen+ilen]
return key, iv
except UnicodeDecodeError:
return None, None
# ================================================================
# encrypt
# ================================================================
def encrypt(password, plaintext, chunkit=True, msgdgst='md5'):
'''
Encrypt the plaintext using the password using an openssl
compatible encryption algorithm. It is the same as creating a file
with plaintext contents and running openssl like this:
$ cat plaintext
<plaintext>
$ openssl enc -e -aes-256-cbc -base64 -salt \\
-pass pass:<password> -n plaintext
@param password The password.
@param plaintext The plaintext to encrypt.
@param chunkit Flag that tells encrypt to split the ciphertext
into 64 character (MIME encoded) lines.
This does not affect the decrypt operation.
@param msgdgst The message digest algorithm.
'''
salt = os.urandom(8)
key, iv = get_key_and_iv(password, salt, msgdgst=msgdgst)
if key is None:
return None
# PKCS#7 padding
padding_len = 16 - (len(plaintext) % 16)
if isinstance(plaintext, str):
padded_plaintext = plaintext + (chr(padding_len) * padding_len)
else: # assume bytes
padded_plaintext = plaintext + (bytearray([padding_len] * padding_len))
# Encrypt
cipher = AES.new(key, AES.MODE_CBC, iv)
ciphertext = cipher.encrypt(padded_plaintext)
# Make openssl compatible.
# I first discovered this when I wrote the C++ Cipher class.
# CITATION: http://projects.joelinoff.com/cipher-1.1/doxydocs/html/
openssl_ciphertext = b'Salted__' + salt + ciphertext
b64 = base64.b64encode(openssl_ciphertext)
if not chunkit:
return b64
LINELEN = 64
chunk = lambda s: b'\n'.join(s[i:min(i+LINELEN, len(s))]
for i in range(0, len(s), LINELEN))
return chunk(b64)
# ================================================================
# decrypt
# ================================================================
def decrypt(password, ciphertext, msgdgst='md5'):
'''
Decrypt the ciphertext using the password using an openssl
compatible decryption algorithm. It is the same as creating a file
with ciphertext contents and running openssl like this:
$ cat ciphertext
# ENCRYPTED
<ciphertext>
$ egrep -v '^#|^$' | \\
openssl enc -d -aes-256-cbc -base64 -salt -pass pass:<password> -in ciphertext
@param password The password.
@param ciphertext The ciphertext to decrypt.
@param msgdgst The message digest algorithm.
@returns the decrypted data.
'''
# unfilter -- ignore blank lines and comments
if isinstance(ciphertext, str):
filtered = ''
nl = '\n'
re1 = r'^\s*$'
re2 = r'^\s*#'
else:
filtered = b''
nl = b'\n'
re1 = b'^\\s*$'
re2 = b'^\\s*#'
for line in ciphertext.split(nl):
line = line.strip()
if re.search(re1,line) or re.search(re2, line):
continue
filtered += line + nl
# Base64 decode
raw = base64.b64decode(filtered)
assert(raw[:8] == b'Salted__' )
salt = raw[8:16] # get the salt
# Now create the key and iv.
key, iv = get_key_and_iv(password, salt, msgdgst=msgdgst)
if key is None:
return None
# The original ciphertext
ciphertext = raw[16:]
# Decrypt
cipher = AES.new(key, AES.MODE_CBC, iv)
padded_plaintext = cipher.decrypt(ciphertext)
if isinstance(padded_plaintext, str):
padding_len = ord(padded_plaintext[-1])
else:
padding_len = padded_plaintext[-1]
plaintext = padded_plaintext[:-padding_len]
return plaintext
回答5:
Note: this method is not OpenSSL compatible
But it is suitable if all you want to do is encrypt and decrypt files.
A self-answer I copied from here. I think this is, perhaps, a simpler and more secure option. Although I would be interested in some expert opinion on how secure it is.
I used Python 3.6 and SimpleCrypt to encrypt the file and then uploaded it.
I think this is the code I used to encrypt the file:
from simplecrypt import encrypt, decrypt
f = open('file.csv','r').read()
ciphertext = encrypt('USERPASSWORD',f.encode('utf8')) # I am not certain of whether I used the .encode('utf8')
e = open('file.enc','wb') # file.enc doesn't need to exist, python will create it
e.write(ciphertext)
e.close
This is the code I use to decrypt at runtime, I run getpass("password: ") as an argument so I don't have to store a password variable in memory
from simplecrypt import encrypt, decrypt
from getpass import getpass
# opens the file
f = open('file.enc','rb').read()
print('Please enter the password and press the enter key \n Decryption may take some time')
# Decrypts the data, requires a user-input password
plaintext = decrypt(getpass("password: "), f).decode('utf8')
print('Data have been Decrypted')
Note, the UTF-8 encoding behaviour is different in python 2.7 so the code will be slightly different.
来源：https://stackoverflow.com/questions/16761458/how-to-decrypt-openssl-aes-encrypted-files-in-python