change prng, add warning against encrypting multiple secrets (#4649)

* substitute python prng generator with hmac_drbg

* add warning, change version

* brick cards version 0

* separate python-drbg module, include tests and license

* import to match PEP 8

* fix line break, minor changes in wording

* fixes noise_seed formatting errors

* fix import, include license exclude tests drbg module

electrum/plugins/revealer/hmac_drbg.py

@@ -0,0 +1,51 @@
+'''
+Copyright (c) 2014 David Lazar <lazard@mit.edu>
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.
+'''
+
+import hashlib
+import hmac
+
+class DRBG(object):
+    def __init__(self, seed):
+        self.key = b'\x00' * 64
+        self.val = b'\x01' * 64
+        self.reseed(seed)
+
+    def hmac(self, key, val):
+        return hmac.new(key, val, hashlib.sha512).digest()
+
+    def reseed(self, data=b''):
+        self.key = self.hmac(self.key, self.val + b'\x00' + data)
+        self.val = self.hmac(self.key, self.val)
+
+        if data:
+            self.key = self.hmac(self.key, self.val + b'\x01' + data)
+            self.val = self.hmac(self.key, self.val)
+
+    def generate(self, n):
+        xs = b''
+        while len(xs) < n:
+            self.val = self.hmac(self.key, self.val)
+            xs += self.val
+
+        self.reseed()
+
+        return xs[:n]

electrum/plugins/revealer/qt.py

@@ -22,16 +22,17 @@ import qrcode
 import traceback
 from hashlib import sha256
 from decimal import Decimal
+import binascii
 
 from PyQt5.QtPrintSupport import QPrinter
 
 from electrum.plugin import BasePlugin, hook
 from electrum.i18n import _
 from electrum.util import to_bytes, make_dir
-
 from electrum.gui.qt.util import *
 from electrum.gui.qt.qrtextedit import ScanQRTextEdit
 
+from .hmac_drbg import DRBG
 
 class Plugin(BasePlugin):
 
@@ -47,7 +48,7 @@ class Plugin(BasePlugin):
         self.calibration_h = self.config.get('calibration_h')
         self.calibration_v = self.config.get('calibration_v')
 
-        self.version = '0'
+        self.version = '1'
         self.size = (159, 97)
         self.f_size = QSize(1014*2, 642*2)
         self.abstand_h = 21
@@ -130,7 +131,7 @@ class Plugin(BasePlugin):
         s = self.get_noise()
         b = self.is_noise(s)
         if b:
-            self.noise_seed = s[:-3]
+            self.noise_seed = s[1:-3]
             self.user_input = True
         self.next_button.setEnabled(b)
 
@@ -155,6 +156,9 @@ class Plugin(BasePlugin):
                 else:
                     return False
         else:
+
+            if (len(txt)>0 and txt[0]=='0'):
+                self.d.show_message(''.join(["<b>",_("Warning: "), "</b>", _("Revealers starting with 0 had a vulnerability and are not supported.")]))
             self.user_input = False
             return False
 
@@ -211,12 +215,12 @@ class Plugin(BasePlugin):
         grid = QGridLayout()
         self.vbox.addLayout(grid)
 
-        cprint = QPushButton(_("Generate encrypted seed PDF"))
+        cprint = QPushButton(_("Generate encrypted seed backup"))
         cprint.clicked.connect(partial(self.seed_img, True))
         self.vbox.addWidget(cprint)
         self.vbox.addSpacing(14)
 
-        self.vbox.addWidget(WWLabel(_("and/or type any secret below:")))
+        self.vbox.addWidget(WWLabel(_("OR type any secret below:")))
         self.text = ScanQRTextEdit()
         self.text.setTabChangesFocus(True)
         self.text.setMaximumHeight(70)
@@ -231,12 +235,19 @@ class Plugin(BasePlugin):
         self.vbox.addWidget(self.max_chars)
         self.max_chars.setVisible(False)
 
-        self.ctext = QPushButton(_("Generate custom secret encrypted PDF"))
+        self.ctext = QPushButton(_("Generate custom secret encrypted backup"))
         self.ctext.clicked.connect(self.t)
 
         self.vbox.addWidget(self.ctext)
         self.ctext.setEnabled(False)
 
+        self.vbox.addSpacing(11)
+        self.vbox.addWidget(
+                            QLabel(''.join(["<b>" + _("WARNING") + "</b>: " + _("Revealer is a one-time-pad and should be used only once."), '<br/>',
+                            _("Multiple secrets encrypted for the same Revealer can be attacked."), '<br/>',
+                            ])))
+        self.vbox.addSpacing(11)
+
         self.vbox.addSpacing(21)
         self.vbox.addLayout(Buttons(CloseButton(d)))
         return bool(d.exec_())
@@ -305,21 +316,27 @@ class Plugin(BasePlugin):
 
         if(self.noise_seed == False):
             self.noise_seed = random.SystemRandom().getrandbits(128)
-            self.hex_noise = format(self.noise_seed, '02x')
+            self.hex_noise = format(self.noise_seed, '032x')
             self.hex_noise = self.version + str(self.hex_noise)
 
         if (self.user_input == True):
             self.noise_seed = int(self.noise_seed, 16)
-            self.hex_noise = self.version + str(format(self.noise_seed, '02x'))
-
+            self.hex_noise = self.version + str(format(self.noise_seed, '032x'))
 
         self.code_id = self.code_hashid(self.hex_noise)
         self.hex_noise = ' '.join(self.hex_noise[i:i+4] for i in range(0,len(self.hex_noise),4))
-        random.seed(self.noise_seed)
 
+        entropy = binascii.unhexlify(str(format(self.noise_seed, '032x')))
+        code_id = binascii.unhexlify(self.version + self.code_id)
+
+        drbg = DRBG(entropy + code_id)
+        noise_array=bin(int.from_bytes(drbg.generate(1929), 'big'))[2:]
+
+        i=0
         for x in range(w):
             for y in range(h):
-                rawnoise.setPixel(x,y,random.randint(0, 1))
+                rawnoise.setPixel(x,y,int(noise_array[i]))
+                i+=1
 
         self.rawnoise = rawnoise
         if create_revealer==True: