initial commit

src/passphrase.nim

@@ -0,0 +1,83 @@
+import std/[os, strutils]
+import nimcrypto/sysrand
+
+
+type Dictionary = object
+  words: string
+  offsets: seq[uint32]
+
+
+proc `[]`(d: Dictionary, i: Natural): string =
+  # last word has no following start index, so we have to fake it
+  # also strings are indexed with ints
+  let slice = if i == d.offsets.high:
+    d.offsets[i].int .. d.words.high
+  else:
+    d.offsets[i].int ..< d.offsets[i + 1].int
+
+  result = d.words[slice]
+
+
+proc len(d: Dictionary): int =
+  result = d.offsets.len
+
+
+proc loadWords(): Dictionary =
+  for word in staticRead("dictionary.txt").strip().splitLines():
+    let startIdx = result.words.len.uint32
+    result.offsets.add(startIdx)
+    result.words.add(word)
+
+
+const dict = loadWords()
+
+
+proc genPassphrase(length, dictSize: int): string =
+  if dictSize < 100 or dictSize > dict.len:
+    quit("Dictionary size must be between 100 and " & $dict.len, 1)
+
+  var rands = newSeq[uint64](length)
+  discard randomBytes(rands)
+
+  var words: seq[string]
+  for r in rands:
+    let i = r mod dictSize.uint64
+    words.add(dict[i])
+  result = words.join(" ")
+
+
+const help = """Usage:
+  passphrase [LENGTH] [DICTSIZE]
+
+Defaults to length of 4 and dictionary size of 25,000."""
+
+proc parseInput(): (int, int) =
+  let params = commandLineParams()
+  if "-h" in params or "--help" in params:
+    echo help
+    quit(0)
+
+  var
+    length = 4
+    dictSize = 25_000
+
+  if params.len > 0:
+    try:
+      length = parseInt(params[0])
+    except ValueError:
+      quit(params[0] & " is not a valid passphrase length.", 1)
+
+  if params.len > 1:
+    try:
+      dictSize = parseInt(params[1])
+      if dictSize < 100 or dictSize > dict.len:
+        quit("Dictionary size must be between 100 and " & $dict.len, 1)
+    except ValueError:
+      quit(params[1] & " is not a valid dictionary size.", 1)
+
+  result = (length, dictSize)
+
+
+when isMainModule:
+  let (length, dictSize) = parseInput()
+  echo genPassphrase(length, dictSize)