expand readme - include custom formats

README.md

@@ -63,3 +63,17 @@ Tools for sharing secrets (like Bitcoin private keys), using shamir's secret sha
 
     >>> points_to_secret_int(shares[0:2])
     88985120633792790105905686761572077713049967498756747774697023364147812997770L
+
+### Custom formats
+
+#### Splitting into shares
+
+    >>> from secretsharing import SecretSharer, base64_chars, base16_chars
+    >>> sharer = SecretSharer(secret_charset=base16_chars, share_charset=base64_chars)
+    >>> shares = sharer.split_secret("c4bbcb1fbec99d65bf59d85c8cb62ee2db963f0fe106f483d9afa73bd4e39a8a", 2, 3)
+    ['B-JpxCTUQ9D+q93JglQM9yRinI2Cyxe92FTBSYa93ppfY', 'C-HAmR0pjHuHwL4rozXnFY05ysIJVqtf3pob1HCMaaZUm', 'D-EXbhV+1SYQ1Z6NxBfBM/YQ+PaP4j8B5N92X1pa9LJJ0']
+
+#### Recovering from shares
+
+    >>> sharer.recover_secret(shares[0:2])
+    'c4bbcb1fbec99d65bf59d85c8cb62ee2db963f0fe106f483d9afa73bd4e39a8a'

secretsharing/__init__.py

@@ -10,4 +10,4 @@
 __version__ = '0.2.0'
 
 from .sharing import *
-from .charset import charset_to_int, int_to_charset
+from .charset import *

secretsharing/charset.py

@@ -42,6 +42,11 @@ def change_charset(s, original_charset, target_charset):
     output_string = int_to_charset(intermediate_integer, target_charset)
     return output_string
 
+""" Base16 includes numeric digits and the letters a through f. Here,
+    we use the lowecase letters.
+"""
+base16_chars = string.hexdigits[0:16]
+
 """ The Base58 character set allows for strings that avoid visual ambiguity
     when typed. It consists of all the alphanumeric characters except for
     "0", "O", "I", and "l", which look similar in some fonts.