diceware: add passphrase generator

1 files changed, 42 insertions, 0 deletions

diff --git a/passgen/diceware/src/main/kotlin/dev/msfjarvis/aps/passgen/diceware/DicewarePassphraseGenerator.kt b/passgen/diceware/src/main/kotlin/dev/msfjarvis/aps/passgen/diceware/DicewarePassphraseGenerator.kt
new file mode 100644
index 00000000..ee18352e
--- /dev/null
+++ b/passgen/diceware/src/main/kotlin/dev/msfjarvis/aps/passgen/diceware/DicewarePassphraseGenerator.kt
@@ -0,0 +1,42 @@
+/*
+ * Copyright © 2014-2021 The Android Password Store Authors. All Rights Reserved.
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+package dev.msfjarvis.aps.passgen.diceware
+
+import java.io.InputStream
+import javax.inject.Inject
+
+/**
+ * Password generator implementing the Diceware passphrase generation mechanism. For detailed
+ * information on how this works, see https://theworld.com/~reinhold/diceware.html.
+ */
+public class DicewarePassphraseGenerator
+@Inject
+constructor(
+  private val die: Die,
+  wordList: InputStream,
+) {
+
+  private val wordMap = WordListParser.parse(wordList)
+
+  /** Generates a passphrase with [wordCount] words. */
+  public fun generatePassphrase(wordCount: Int, separator: Char): String {
+    return StringBuilder()
+      .apply {
+        repeat(wordCount) { idx ->
+          append(wordMap[die.rollMultiple(DIGITS)])
+          if (idx < wordCount - 1) append(separator)
+        }
+      }
+      .toString()
+      .trimEnd()
+  }
+
+  private companion object {
+
+    /** Number of digits used by indices in the default wordlist. */
+    const val DIGITS: Int = 5
+  }
+}