Add calculation for password entropy

Remove default password length, calculate it instead based on ENTROPY_BITS_MIN.
Warn when password is too short.

README.md

@@ -12,17 +12,19 @@ It also makes use of the [EFF Large Wordlist](https://www.eff.org/es/document/pa
 
 A secure passphrase must be of at least 6 words, but 7 is better, and maybe you can add a random number to the list. If you need a password, make it bigger than 8 characters (NIST's latest recommendation), and preffer more than 12 (I recommend 16 or more). Passwords are comprised of digits, upper and lower case letters and punctuation symbols - more specifically: `ascii_letters`, `digits` and `punctuation` from [Lib/string](https://docs.python.org/3.6/library/string.html#string-constants) -.
 
-If you specify a list different than the EFF Large Wordlist, the minimum amount of words for a passphrase to be secure changes: for shorter lists, the amount increases. **Passphrase** calculates the minimum secure amount of words automatically and warns if the chosen number is low.
+If you specify a list different than the EFF Large Wordlist, the minimum amount of words for a passphrase to be secure changes: for shorter lists, the amount increases. **Passphrase** calculates the minimum secure amount of words automatically and warns if the chosen number is low. It does the same for a password if it is too short.
 
 ## Requirements
 
 For **Python 3.6+**:
 
+* numpy 1.13+ [optional] for faster entropy computation
 * flake8 [optional] for linting
 
 For **Python 3.2+**:
 
 * LibNaCl 1.5+
+* numpy 1.13+ [optional] for faster entropy computation
 * flake8 [optional] for linting
 
 [passphrase.py](/src/passphrase.py) is a stand-alone, self contained script (the word list is embedded in it). It detects whether you have Python 3.6+ or lower, and acts accordingly. For Python 3.6+, it uses `Lib/secrets` (and is preferred); for Python 3.2+, `libnacl.randombytes_uniform`.
@@ -63,10 +65,10 @@ E`31nDL0^$oYu5='
 #### Use an external wordlist to generate a passphrase
 
 ```
-:~$ passphrase -i my-wordlist.txt
-anguished estate placard deceptive entity
-:~$ passphrase -d -i my-dicewarelike-wordlist.txt
-unnamed unmanned appendix fineness riverside
+:~$ passphrase -i eff_short_wordlist_1_1column.txt
+wimp broke dash pasta zebra viral outer clasp
+:~$ passphrase -d -i eff_short_wordlist_1.txt 
+mouse trend coach stain shut rhyme baggy scale
 ```
 
 #### Save the output to a file

man/passphrase.1

@@ -12,7 +12,7 @@ password, and prints it to standard output.
 By default, it uses an embedded EFF Large Wordlist for passphrases.
 Passphrases with less than 6 words are considered insecure. A safe bet is
 between 6 and 7 words, plus at least a number.
-For passwords, use at least 8 characters, but prefer 12 or more.
+For passwords, use at least 12 characters, but prefer 16 or more.
 .PP
 Instead of words and numbers, a password (random string of printable
 characters from Python String standard) can be generated by

man/passphrase.md

@@ -16,8 +16,8 @@ Generates a cryptographically secure passphrase, based on a wordlist, or
 a password, and prints it to standard output. By default, it uses an
 embedded EFF Large Wordlist for passphrases. Passphrases with less than
 6 words are considered insecure. A safe bet is between 6 and 7 words,
-plus at least a number. For passwords, use at least 8 characters, but
-prefer 12 or more.
+plus at least a number. For passwords, use at least 12 characters, but
+prefer 16 or more.
 
 Instead of words and numbers, a password (random string of printable
 characters from Python String standard) can be generated by **-p** |

src/passphrase.py

@@ -7796,13 +7796,12 @@
     'zoom'
 )
 
-VERSION = '0.2.4'
+VERSION = '0.2.5'
 
 MAX_NUM = 999999
 MIN_NUM = 100000
 WORDS_AMOUNT_MIN_DEFAULT = 6  # Just for EFF's Large Wordlist
 NUMS_AMOUNT_MIN_DEFAULT = 0
-PASSWD_LEN_MIN_DEFAULT = 8  # From NIST's recomendation: http://bit.ly/2bpkyBc
 ENTROPY_BITS_MIN = 77  # From EFF's post: http://bit.ly/2p96a2a
 
 
@@ -7928,6 +7927,9 @@ def generate_password(length: int) -> str:
     import argparse
     from sys import exit
 
+    # entropy_bits(list(characters)) = 6.554588
+    PASSWD_LEN_MIN_GOOD = ceil(ENTROPY_BITS_MIN / 6.554588)
+
     parser = argparse.ArgumentParser(
         formatter_class=argparse.RawDescriptionHelpFormatter,
         description='Passphrase v{version} - Copyright HacKan '
@@ -7963,8 +7965,8 @@ def generate_password(length: int) -> str:
             maxnum=MAX_NUM,
             wordsamountmin=WORDS_AMOUNT_MIN_DEFAULT,
             numsamountmin=NUMS_AMOUNT_MIN_DEFAULT,
-            passwdmin=PASSWD_LEN_MIN_DEFAULT,
-            passwdpref=PASSWD_LEN_MIN_DEFAULT + 4,
+            passwdmin=PASSWD_LEN_MIN_GOOD,
+            passwdpref=PASSWD_LEN_MIN_GOOD + 4,
             version=VERSION
         )
     )
@@ -7986,7 +7988,7 @@ def generate_password(length: int) -> str:
         "-p",
         "--password",
         type=bigger_than_zero,
-        const=PASSWD_LEN_MIN_DEFAULT,
+        const=PASSWD_LEN_MIN_GOOD,
         nargs='?',
         help="generate a password of specified lenght from all printable "
              "characters"
@@ -8060,6 +8062,12 @@ def generate_password(length: int) -> str:
         exit()
 
     if passwordlen is not None:
+        if passwordlen < PASSWD_LEN_MIN_GOOD:
+            print_stderr(
+                "Warning: Insecure password length chosen! Should be bigger "
+                "than or equal to {}".format(PASSWD_LEN_MIN_GOOD)
+            )
+
         passphrase = generate_password(passwordlen)
         separator = ''
     else:
@@ -8070,21 +8078,23 @@ def generate_password(length: int) -> str:
         # Then: entropy_w * amount_w + entropy_n * amount_n >= ENTROPY_BITS_MIN
         entropy_n = entropy_bits_nrange(MIN_NUM, MAX_NUM)
         entropy_w = entropy_bits(words)
-        amount_w_e = (ENTROPY_BITS_MIN - entropy_n * amount_n) / entropy_w
+        amount_w_good_e = (ENTROPY_BITS_MIN - entropy_n * amount_n) / entropy_w
         # print("entropy_n={}".format(entropy_n))
         # print("entropy_w={}".format(entropy_w))
-        # print("amount_w_e={}".format(amount_w_e))
+        # print("amount_w_good_e={}".format(amount_w_good_e))
 
-        if amount_w_e > -1:
-            amount_w_default = ceil(abs(amount_w_e))
+        if amount_w_good_e > -1:
+            amount_w_good = ceil(abs(amount_w_good_e))
         else:
-            amount_w_default = 0
+            amount_w_good = 0
 
         if amount_w is None:
-            amount_w = amount_w_default
-        elif amount_w < amount_w_default:
-            print_stderr("Warning: Insecure amount of words chosen! Should be "
-                         "bigger than or equal to {}".format(amount_w_default))
+            amount_w = amount_w_good
+        elif amount_w < amount_w_good:
+            print_stderr(
+                "Warning: Insecure amount of words chosen! Should be "
+                "bigger than or equal to {}".format(amount_w_good)
+            )
 
         passphrase = generate(wordlist=words, amount_w=amount_w,
                               amount_n=amount_n)