From c5436b543df466657a1d0dc3af40d4707fca9b9d Mon Sep 17 00:00:00 2001
From: Harsh Shandilya <me@msfjarvis.dev>
Date: Fri, 10 Dec 2021 13:59:32 +0530
Subject: [PATCH] diceware: add passphrase generator

---
 passgen/diceware/api/diceware.api             |  6 +++
 .../diceware/DicewarePassphraseGenerator.kt   | 42 +++++++++++++++++++
 .../DicewarePassphraseGeneratorTest.kt        | 29 +++++++++++++
 3 files changed, 77 insertions(+)
 create mode 100644 passgen/diceware/src/main/kotlin/dev/msfjarvis/aps/passgen/diceware/DicewarePassphraseGenerator.kt
 create mode 100644 passgen/diceware/src/test/kotlin/dev/msfjarvis/aps/passgen/diceware/DicewarePassphraseGeneratorTest.kt

diff --git a/passgen/diceware/api/diceware.api b/passgen/diceware/api/diceware.api
index 8d16ae8f..925d6739 100644
--- a/passgen/diceware/api/diceware.api
+++ b/passgen/diceware/api/diceware.api
@@ -1,3 +1,9 @@
+public final class dev/msfjarvis/aps/passgen/diceware/DicewarePassphraseGenerator {
+	public static final field DIGITS I
+	public fun <init> (Ldev/msfjarvis/aps/passgen/diceware/Die;Ljava/io/InputStream;)V
+	public final fun generatePassphrase (IC)Ljava/lang/String;
+}
+
 public final class dev/msfjarvis/aps/passgen/diceware/Die {
 	public fun <init> (ILdev/msfjarvis/aps/passgen/diceware/RandomIntGenerator;)V
 	public final fun roll ()I
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
+  }
+}
diff --git a/passgen/diceware/src/test/kotlin/dev/msfjarvis/aps/passgen/diceware/DicewarePassphraseGeneratorTest.kt b/passgen/diceware/src/test/kotlin/dev/msfjarvis/aps/passgen/diceware/DicewarePassphraseGeneratorTest.kt
new file mode 100644
index 00000000..7f22fdcc
--- /dev/null
+++ b/passgen/diceware/src/test/kotlin/dev/msfjarvis/aps/passgen/diceware/DicewarePassphraseGeneratorTest.kt
@@ -0,0 +1,29 @@
+/*
+ * 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 kotlin.random.Random
+import kotlin.test.assertEquals
+import org.junit.Test
+
+class DicewarePassphraseGeneratorTest {
+  /** Pre-seeded [Random] instance to ensure tests are deterministic. */
+  private val random = Random(1_00_000)
+
+  private val intGenerator = RandomIntGenerator { it.random(random) }
+  @Test
+  fun generate_passphrase() {
+    val die = Die(6, intGenerator)
+
+    val generator =
+      DicewarePassphraseGenerator(
+        die,
+        WordListParserTest.getDefaultWordList(),
+      )
+
+    assertEquals("salvation_cozily_croon_trustee_fidgety", generator.generatePassphrase(5, '_'))
+  }
+}