zerobinpaste: use 48b keys (only 6 chars) by default

tools/zerobinpaste.coffee

@@ -5,7 +5,12 @@ program
     .option('-u, --url [url]', 'URL of a 0bin site.')
     .option('-e, --expire [period]',
         'Expiration period - one of: 1_view, 1_day (default), 1_month, never.', '1_day')
-    .option('-c, --config [path]', 'Path to zerobin configuration file (default: ~/.zerobinpasterc).\n'\
+    .option('-k, --entropy [bits]',
+        'Encryption key entropy (and hence length) to use,'\
+        + ' in bits, rounded up to multiple of 6 (default: 48).\n'\
+        + '   That key will be processed by 1000 pbkdf2-sha256 iterations, not used as-is.', 48)
+    .option('-c, --config [path]',
+        'Path to zerobin configuration file (default: ~/.zerobinpasterc).\n'\
         + '   Should be json-file with the same keys as can be specified on the command line.\n'\
         + '   Example contents: {"url": "http://some-0bin.com"}', '~/.zerobinpasterc')
     .parse(process.argv);
@@ -40,6 +45,17 @@ if program.expire not in expire_opts
         + ' must be one of: ' + expire_opts.join(', ') + "." )
     process.exit(1)
 
+program.entropy = parseInt(program.entropy)
+
+
+# Generated key will use base64 (6b per char) charset
+# Key is not decoded for pbkdf2, so it's generated via base64 here just for convenience
+generate_key = (entropy) ->
+    entropy = Math.ceil(entropy / 6) * 6 # non-6-multiple produces same-length base64
+    key = sjcl.bitArray.clamp(
+        sjcl.random.randomWords(Math.ceil(entropy / 32), 0), entropy )
+    return sjcl.codec.base64.fromBits(key, 0).replace(/\=+$/, '').replace(/\//, '-')
+
 
 # Paste one dump and print URL, optionally prefixed with name
 paste_file = (content, name) ->
@@ -48,7 +64,7 @@ paste_file = (content, name) ->
     content = sjcl.codec.base64.fromBits(content)
     # content = lzw.compress(content)
 
-    key = sjcl.codec.base64.fromBits(sjcl.random.randomWords(8, 0), 0)
+    key = generate_key(program.entropy)
     content = sjcl.encrypt(key, content)
     content = qs.stringify
         content: content