format-common: initial API for PasswordEntry

Signed-off-by: Harsh Shandilya <me@msfjarvis.dev>

4 files changed, 337 insertions, 0 deletions

diff --git a/format-common/src/main/kotlin/dev/msfjarvis/aps/data/passfile/PasswordEntry.kt b/format-common/src/main/kotlin/dev/msfjarvis/aps/data/passfile/PasswordEntry.kt
new file mode 100644
index 00000000..9b7fc8f3
--- /dev/null
+++ b/format-common/src/main/kotlin/dev/msfjarvis/aps/data/passfile/PasswordEntry.kt
@@ -0,0 +1,211 @@
+/*
+ * Copyright © 2014-2021 The Android Password Store Authors. All Rights Reserved.
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+package dev.msfjarvis.aps.data.passfile
+
+import androidx.annotation.VisibleForTesting
+import com.github.michaelbull.result.mapBoth
+import dagger.assisted.Assisted
+import dagger.assisted.AssistedInject
+import dev.msfjarvis.aps.util.time.UserClock
+import dev.msfjarvis.aps.util.totp.Otp
+import dev.msfjarvis.aps.util.totp.TotpFinder
+import kotlin.collections.set
+import kotlin.time.ExperimentalTime
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.delay
+import kotlinx.coroutines.flow.MutableStateFlow
+import kotlinx.coroutines.flow.StateFlow
+import kotlinx.coroutines.flow.asStateFlow
+import kotlinx.coroutines.launch
+
+/** Represents a single entry in the password store. */
+@OptIn(ExperimentalTime::class)
+public class PasswordEntry
+@AssistedInject
+constructor(
+  /** A time source used to calculate the TOTP */
+  clock: UserClock,
+  /** [TotpFinder] implementation to extract data from a TOTP URI */
+  totpFinder: TotpFinder,
+  /**
+   * A cancellable [CoroutineScope] inside which we constantly emit new TOTP values as time elapses
+   */
+  @Assisted scope: CoroutineScope,
+  /** The content of this entry, as an array of bytes. */
+  @Assisted bytes: ByteArray,
+) {
+
+  private val _totp = MutableStateFlow("")
+  private val content = bytes.decodeToString()
+
+  /** The password text for this entry. Can be null. */
+  public val password: String?
+
+  /** The username for this entry. Can be null. */
+  public val username: String?
+
+  /** A [String] to [String] [Map] of the extra content of this entry, in a key:value fashion. */
+  public val extraContent: Map<String, String>
+
+  /**
+   * A [StateFlow] providing the current TOTP. It will emit a single empty string on initialization
+   * which is replaced with a real TOTP if applicable. Call [hasTotp] to verify whether or not you
+   * need to observe this value.
+   */
+  public val totp: StateFlow<String> = _totp.asStateFlow()
+
+  /**
+   * String representation of [extraContent] but with authentication related data such as TOTP URIs
+   * and usernames stripped.
+   */
+  public val extraContentWithoutAuthData: String
+  private val digits: String
+  private val totpSecret: String?
+  private val totpPeriod: Long
+  private val totpAlgorithm: String
+  @VisibleForTesting(otherwise = VisibleForTesting.PRIVATE) internal val extraContentString: String
+
+  init {
+    val (foundPassword, passContent) = findAndStripPassword(content.split("\n".toRegex()))
+    password = foundPassword
+    extraContentString = passContent.joinToString("\n")
+    extraContentWithoutAuthData = generateExtraContentWithoutAuthData()
+    extraContent = generateExtraContentPairs()
+    username = findUsername()
+    digits = totpFinder.findDigits(content)
+    totpSecret = totpFinder.findSecret(content)
+    totpPeriod = totpFinder.findPeriod(content)
+    totpAlgorithm = totpFinder.findAlgorithm(content)
+    if (totpSecret != null) {
+      scope.launch {
+        updateTotp(clock.millis())
+        val remainingTime = totpPeriod - (System.currentTimeMillis() % totpPeriod)
+        delay(remainingTime)
+        repeat(Int.MAX_VALUE) {
+          updateTotp(clock.millis())
+          delay(totpPeriod)
+        }
+      }
+    }
+  }
+
+  public fun hasTotp(): Boolean {
+    return totpSecret != null
+  }
+
+  private fun findAndStripPassword(passContent: List<String>): Pair<String?, List<String>> {
+    if (TotpFinder.TOTP_FIELDS.any { passContent[0].startsWith(it) }) return Pair(null, passContent)
+    for (line in passContent) {
+      for (prefix in PASSWORD_FIELDS) {
+        if (line.startsWith(prefix, ignoreCase = true)) {
+          return Pair(line.substring(prefix.length).trimStart(), passContent.minus(line))
+        }
+      }
+    }
+    return Pair(passContent[0], passContent.minus(passContent[0]))
+  }
+
+  private fun generateExtraContentWithoutAuthData(): String {
+    var foundUsername = false
+    return extraContentString
+      .lineSequence()
+      .filter { line ->
+        return@filter when {
+          USERNAME_FIELDS.any { prefix -> line.startsWith(prefix, ignoreCase = true) } && !foundUsername -> {
+            foundUsername = true
+            false
+          }
+          line.startsWith("otpauth://", ignoreCase = true) || line.startsWith("totp:", ignoreCase = true) -> {
+            false
+          }
+          else -> {
+            true
+          }
+        }
+      }
+      .joinToString(separator = "\n")
+  }
+
+  private fun generateExtraContentPairs(): Map<String, String> {
+    fun MutableMap<String, String>.putOrAppend(key: String, value: String) {
+      if (value.isEmpty()) return
+      val existing = this[key]
+      this[key] =
+        if (existing == null) {
+          value
+        } else {
+          "$existing\n$value"
+        }
+    }
+
+    val items = mutableMapOf<String, String>()
+    // Take extraContentWithoutAuthData and onEach line perform the following tasks
+    extraContentWithoutAuthData.lines().forEach { line ->
+      // Split the line on ':' and save all the parts into an array
+      // "ABC : DEF:GHI" --> ["ABC", "DEF", "GHI"]
+      val splitArray = line.split(":")
+      // Take the first element of the array. This will be the key for the key-value pair.
+      // ["ABC ", " DEF", "GHI"] -> key = "ABC"
+      val key = splitArray.first().trimEnd()
+      // Remove the first element from the array and join the rest of the string again with
+      // ':' as separator.
+      // ["ABC ", " DEF", "GHI"] -> value = "DEF:GHI"
+      val value = splitArray.drop(1).joinToString(":").trimStart()
+
+      if (key.isNotEmpty() && value.isNotEmpty()) {
+        // If both key and value are not empty, we can form a pair with this so add it to
+        // the map.
+        // key = "ABC", value = "DEF:GHI"
+        items[key] = value
+      } else {
+        // If either key or value is empty, we were not able to form proper key-value pair.
+        // So append the original line into an "EXTRA CONTENT" map entry
+        items.putOrAppend(EXTRA_CONTENT, line)
+      }
+    }
+
+    return items
+  }
+
+  private fun findUsername(): String? {
+    extraContentString.splitToSequence("\n").forEach { line ->
+      for (prefix in USERNAME_FIELDS) {
+        if (line.startsWith(prefix, ignoreCase = true)) return line.substring(prefix.length).trimStart()
+      }
+    }
+    return null
+  }
+
+  private fun updateTotp(millis: Long) {
+    if (totpSecret != null) {
+      Otp.calculateCode(totpSecret, millis / (1000 * totpPeriod), totpAlgorithm, digits)
+        .mapBoth({ code -> _totp.value = code }, { throwable -> throw throwable })
+    }
+  }
+
+  internal companion object {
+
+    private const val EXTRA_CONTENT = "Extra Content"
+    internal val USERNAME_FIELDS =
+      arrayOf(
+        "login:",
+        "username:",
+        "user:",
+        "account:",
+        "email:",
+        "name:",
+        "handle:",
+        "id:",
+        "identity:",
+      )
+    internal val PASSWORD_FIELDS =
+      arrayOf(
+        "password:",
+        "secret:",
+        "pass:",
+      )
+  }
+}
diff --git a/format-common/src/main/kotlin/dev/msfjarvis/aps/util/time/Clocks.kt b/format-common/src/main/kotlin/dev/msfjarvis/aps/util/time/Clocks.kt
new file mode 100644
index 00000000..087a5028
--- /dev/null
+++ b/format-common/src/main/kotlin/dev/msfjarvis/aps/util/time/Clocks.kt
@@ -0,0 +1,26 @@
+/*
+ * Copyright © 2014-2021 The Android Password Store Authors. All Rights Reserved.
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+package dev.msfjarvis.aps.util.time
+
+import java.time.Clock
+import java.time.Instant
+import java.time.ZoneId
+import javax.inject.Inject
+
+/**
+ * A subclass of [Clock] that uses [Clock.systemDefaultZone] to get a clock that works for the
+ * user's current time zone.
+ */
+public open class UserClock @Inject constructor() : Clock() {
+
+  private val clock = systemDefaultZone()
+
+  override fun withZone(zone: ZoneId): Clock = clock.withZone(zone)
+
+  override fun getZone(): ZoneId = clock.zone
+
+  override fun instant(): Instant = clock.instant()
+}
diff --git a/format-common/src/main/kotlin/dev/msfjarvis/aps/util/totp/Otp.kt b/format-common/src/main/kotlin/dev/msfjarvis/aps/util/totp/Otp.kt
new file mode 100644
index 00000000..e6efd794
--- /dev/null
+++ b/format-common/src/main/kotlin/dev/msfjarvis/aps/util/totp/Otp.kt
@@ -0,0 +1,74 @@
+/*
+ * Copyright © 2014-2021 The Android Password Store Authors. All Rights Reserved.
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+package dev.msfjarvis.aps.util.totp
+
+import com.github.michaelbull.result.Err
+import com.github.michaelbull.result.runCatching
+import java.nio.ByteBuffer
+import java.util.Locale
+import javax.crypto.Mac
+import javax.crypto.spec.SecretKeySpec
+import kotlin.experimental.and
+import org.apache.commons.codec.binary.Base32
+
+internal object Otp {
+
+  private val BASE_32 = Base32()
+  private val STEAM_ALPHABET = "23456789BCDFGHJKMNPQRTVWXY".toCharArray()
+
+  init {
+    check(STEAM_ALPHABET.size == 26)
+  }
+
+  fun calculateCode(secret: String, counter: Long, algorithm: String, digits: String) = runCatching {
+    val algo = "Hmac${algorithm.toUpperCase(Locale.ROOT)}"
+    val decodedSecret = BASE_32.decode(secret)
+    val secretKey = SecretKeySpec(decodedSecret, algo)
+    val digest =
+      Mac.getInstance(algo).run {
+        init(secretKey)
+        doFinal(ByteBuffer.allocate(8).putLong(counter).array())
+      }
+    // Least significant 4 bits are used as an offset into the digest.
+    val offset = (digest.last() and 0xf).toInt()
+    // Extract 32 bits at the offset and clear the most significant bit.
+    val code = digest.copyOfRange(offset, offset + 4)
+    code[0] = (0x7f and code[0].toInt()).toByte()
+    val codeInt = ByteBuffer.wrap(code).int
+    check(codeInt > 0)
+    if (digits == "s") {
+      // Steam
+      var remainingCodeInt = codeInt
+      buildString {
+        repeat(5) {
+          append(STEAM_ALPHABET[remainingCodeInt % 26])
+          remainingCodeInt /= 26
+        }
+      }
+    } else {
+      // Base 10, 6 to 10 digits
+      val numDigits = digits.toIntOrNull()
+      when {
+        numDigits == null -> {
+          return Err(IllegalArgumentException("Digits specifier has to be either 's' or numeric"))
+        }
+        numDigits < 6 -> {
+          return Err(IllegalArgumentException("TOTP codes have to be at least 6 digits long"))
+        }
+        numDigits > 10 -> {
+          return Err(IllegalArgumentException("TOTP codes can be at most 10 digits long"))
+        }
+        else -> {
+          // 2^31 = 2_147_483_648, so we can extract at most 10 digits with the first one
+          // always being 0, 1, or 2. Pad with leading zeroes.
+          val codeStringBase10 = codeInt.toString(10).padStart(10, '0')
+          check(codeStringBase10.length == 10)
+          codeStringBase10.takeLast(numDigits)
+        }
+      }
+    }
+  }
+}
diff --git a/format-common/src/main/kotlin/dev/msfjarvis/aps/util/totp/TotpFinder.kt b/format-common/src/main/kotlin/dev/msfjarvis/aps/util/totp/TotpFinder.kt
new file mode 100644
index 00000000..64f22065
--- /dev/null
+++ b/format-common/src/main/kotlin/dev/msfjarvis/aps/util/totp/TotpFinder.kt
@@ -0,0 +1,26 @@
+/*
+ * Copyright © 2014-2021 The Android Password Store Authors. All Rights Reserved.
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+package dev.msfjarvis.aps.util.totp
+
+/** Defines a class that can extract relevant parts of a TOTP URL for use by the app. */
+public interface TotpFinder {
+
+  /** Get the TOTP secret from the given extra content. */
+  public fun findSecret(content: String): String?
+
+  /** Get the number of digits required in the final OTP. */
+  public fun findDigits(content: String): String
+
+  /** Get the TOTP timeout period. */
+  public fun findPeriod(content: String): Long
+
+  /** Get the algorithm for the TOTP secret. */
+  public fun findAlgorithm(content: String): String
+
+  public companion object {
+    public val TOTP_FIELDS: Array<String> = arrayOf("otpauth://totp", "totp:")
+  }
+}