diff --git a/modoboa/lib/cryptutils.py b/modoboa/lib/cryptutils.py
index 1cfcd5089..758a75052 100644
--- a/modoboa/lib/cryptutils.py
+++ b/modoboa/lib/cryptutils.py
@@ -9,7 +9,8 @@ import string
 
 from django.utils.encoding import force_bytes, force_text
 
-from Crypto.Cipher import AES
+from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
+from cryptography.hazmat.backends import default_backend
 
 from modoboa.parameters import tools as param_tools
 
@@ -29,27 +30,27 @@ def random_key(l=16):
 
 
 def encrypt(clear):
+    key = force_bytes(
+        param_tools.get_global_parameter("secret_key", app="core"))
+    backend = default_backend()
+    cipher = Cipher(algorithms.AES(key), modes.ECB(), backend=backend)
+    encryptor = cipher.encryptor()
+    block_size = algorithms.AES.block_size
+    if len(clear) % block_size:
+        clear += " " * (block_size - len(clear) % block_size)
+    ct = encryptor.update(force_bytes(clear)) + encryptor.finalize()
+    return force_text(base64.b64encode(ct))
+
+
+def decrypt(ct):
+    backend = default_backend()
     key = param_tools.get_global_parameter("secret_key", app="core")
-    obj = AES.new(key, AES.MODE_ECB)
-    if type(clear) is str:
-        clear = clear.encode("utf-8")
-    if len(clear) % AES.block_size:
-        clear += (
-            force_bytes(" ") * (AES.block_size - len(clear) % AES.block_size)
-        )
-    ciph = obj.encrypt(clear)
-    ciph = base64.b64encode(ciph)
-    return force_text(ciph)
-
-
-def decrypt(ciph):
-    obj = AES.new(
-        param_tools.get_global_parameter(
-            "secret_key", app="core"), AES.MODE_ECB
-    )
-    ciph = base64.b64decode(ciph)
-    clear = obj.decrypt(ciph)
-    return clear.rstrip(' ')
+    cipher = Cipher(
+        algorithms.AES(force_bytes(key)), modes.ECB(), backend=backend)
+    ct = base64.b64decode(force_bytes(ct))
+    decryptor = cipher.decryptor()
+    clear = decryptor.update(ct) + decryptor.finalize()
+    return force_text(clear.rstrip(b" "))
 
 
 def get_password(request):
diff --git a/modoboa/lib/email_utils.py b/modoboa/lib/email_utils.py
index a0a3aaa74..123478f1e 100644
--- a/modoboa/lib/email_utils.py
+++ b/modoboa/lib/email_utils.py
@@ -78,7 +78,7 @@ class Email(object):
         """
         fname = msg.get_filename()
         if fname is not None:
-            if type(fname) is six.text_type:
+            if isinstance(fname, six.text_type):
                 fname = fname.encode("utf-8")
             decoded = decode_header(fname)
             value = (
@@ -218,7 +218,9 @@ class Email(object):
             body = lxml.html.tostring(html)
         else:
             body = lxml.html.tostring(body)
-            body = re.sub("<(/?)body", lambda m: "<%sdiv" % m.group(1), body)
+            body = re.sub(
+                "<(/?)body", lambda m: "<%sdiv" % m.group(1),
+                body.decode())
         return body
 
 
@@ -284,7 +286,7 @@ def prepare_addresses(addresses, usage="header"):
             continue
         name, addr = parseaddr(address)
         if name and usage == "header":
-            result.append("%s <%s>" % (Header(name, 'utf8').encode(), addr))
+            result.append("%s <%s>" % (Header(name, 'utf8'), addr))
         else:
             result.append(addr)
     if usage == "header":
diff --git a/modoboa/lib/imap_utf7.py b/modoboa/lib/imap_utf7.py
index f90b13a51..f1a2af3bd 100644
--- a/modoboa/lib/imap_utf7.py
+++ b/modoboa/lib/imap_utf7.py
@@ -53,22 +53,21 @@ http://svn.plone.org/svn/collective/mxmImapClient/trunk/imapUTF7.py
 """
 from __future__ import print_function, unicode_literals
 
-from django.utils.encoding import force_text
-
-import binascii
 import codecs
 
 # encoding
 
+PRINTABLE = set(range(0x20, 0x26)) | set(range(0x27, 0x7f))
 
-def modified_base64(s):
-    s = s.encode('utf-16be')
-    return binascii.b2a_base64(s).rstrip('\n=').replace('/', ',')
+
+def modified_utf7(s):
+    s_utf7 = s.encode('utf-7')
+    return s_utf7[1:-1].replace(b'/', b',')
 
 
 def doB64(_in, r):
     if _in:
-        r.append('&%s-' % modified_base64(''.join(_in)))
+        r.extend([b'&', modified_utf7(''.join(_in)), b'-'])
         del _in[:]
 
 
@@ -76,44 +75,44 @@ def encoder(s):
     r = []
     _in = []
     for c in s:
-        ordC = ord(c)
-        if 0x20 <= ordC <= 0x25 or 0x27 <= ordC <= 0x7e:
+        if ord(c) in PRINTABLE:
             doB64(_in, r)
-            r.append(c)
+            r.append(c.encode())
         elif c == '&':
             doB64(_in, r)
-            r.append('&-')
+            r.append(b'&-')
         else:
             _in.append(c)
     doB64(_in, r)
-    return (str(''.join(r)), len(s))
+    return (b''.join(r), len(s))
 
 
 # decoding
 
-def modified_unbase64(s):
-    b = binascii.a2b_base64(s.replace(',', '/') + '===')
-    return force_text(b, encoding='utf-16be')
+
+def modified_unutf7(s):
+    s_utf7 = b'+' + s.replace(b',', b'/') + b'-'
+    return s_utf7.decode('utf-7')
 
 
 def decoder(s):
     r = []
-    decode = []
+    decoded = bytearray()
     for c in s:
-        if c == '&' and not decode:
-            decode.append('&')
-        elif c == '-' and decode:
-            if len(decode) == 1:
+        if c == ord('&') and not decoded:
+            decoded.append(ord('&'))
+        elif c == ord('-') and decoded:
+            if len(decoded) == 1:
                 r.append('&')
             else:
-                r.append(modified_unbase64(''.join(decode[1:])))
-            decode = []
-        elif decode:
-            decode.append(c)
+                r.append(modified_unutf7(decoded[1:]))
+            decoded = bytearray()
+        elif decoded:
+            decoded.append(c)
         else:
-            r.append(c)
-    if decode:
-        r.append(modified_unbase64(''.join(decode[1:])))
+            r.append(chr(c))
+    if decoded:
+        r.append(modified_unutf7(decoded[1:]))
     bin_str = ''.join(r)
     return (bin_str, len(s))
 
diff --git a/requirements.txt b/requirements.txt
index e8abbe4ee..8baddd8cf 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -22,7 +22,7 @@ jsonfield==1.0.3
 passlib==1.6.5
 progressbar33==2.4
 py-dateutil==2.2
-pycrypto
+cryptography
 pytz
 requests
 rfc6266