feat(kmp): DerivePath as KMP module + utils portable helpers in commonMain

build.gradle.kts

@@ -66,14 +66,18 @@ dependencies {
 // Isolated Projects forbids. The module lists come from `settings.gradle.kts`; the
 // task depends on each module's test task by *path* — a lazy, cross-project-safe
 // dependency that never configures the other project at configuration time.
-// Android modules expose `testDebugUnitTest`; pure-JVM modules expose `test`.
+// Android modules expose `testDebugUnitTest`; KMP modules expose `testAndroidHostTest`;
+// pure-JVM modules expose `test`.
 @Suppress("UNCHECKED_CAST")
 val androidUnitTestModules = rootProject.extra["flipcash.androidUnitTestModules"] as List<String>
 @Suppress("UNCHECKED_CAST")
 val jvmUnitTestModules = rootProject.extra["flipcash.jvmUnitTestModules"] as List<String>
+@Suppress("UNCHECKED_CAST")
+val kmpUnitTestModules = rootProject.extra["flipcash.kmpUnitTestModules"] as List<String>
 
 tasks.register("flipcashTestDebug") {
     description = "Run testDebug for all Flipcash modules"
     dependsOn(androidUnitTestModules.map { "$it:testDebugUnitTest" })
     dependsOn(jvmUnitTestModules.map { "$it:test" })
+    dependsOn(kmpUnitTestModules.map { "$it:testAndroidHostTest" })
 }

kmp/shared-core/build.gradle.kts

@@ -21,13 +21,15 @@ kotlin {
             baseName = "SharedCore"
             isStatic = true
             export(project(":libs:encryption:base58"))
+            export(project(":libs:encryption:derivepath"))
         }
     }
 
     sourceSets {
         commonMain {
             dependencies {
                 api(project(":libs:encryption:base58"))
+                api(project(":libs:encryption:derivepath"))
             }
         }
     }

libs/encryption/derivepath/build.gradle.kts

@@ -0,0 +1,28 @@
+plugins {
+    kotlin("multiplatform")
+    id("com.android.kotlin.multiplatform.library")
+}
+
+kotlin {
+    android {
+        namespace = "com.getcode.encryption.derivepath"
+        compileSdk = 37
+        minSdk = 29
+        withHostTest {}
+    }
+
+    iosArm64()
+    iosSimulatorArm64()
+    iosX64()
+
+    sourceSets {
+        commonMain {
+            // Pure Kotlin — no external dependencies needed.
+        }
+        commonTest {
+            dependencies {
+                implementation(kotlin("test"))
+            }
+        }
+    }
+}

libs/encryption/derivepath/src/commonMain/kotlin/com/getcode/crypt/DerivePath.kt

@@ -0,0 +1,97 @@
+package com.getcode.crypt
+
+/// Represents a BIP-44/SLIP-10 hierarchical derivation path (e.g. `m/44'/501'/0'/0'`).
+class DerivePath(val indexes: List<Index>, val password: String? = null) {
+    /// Returns the canonical string form of the path (e.g. `m/44'/501'/0'/0'`).
+    fun stringRepresentation(): String {
+        val components = indexes.joinToString(separator) { it.stringRepresentation() }
+        return "$identifier$separator$components"
+    }
+
+    override fun equals(other: Any?): Boolean {
+        if (this === other) return true
+        if (other !is DerivePath) return false
+        if (indexes != other.indexes) return false
+        return true
+    }
+
+    override fun hashCode(): Int {
+        return indexes.hashCode()
+    }
+
+    /// A single index component of a derivation path, optionally hardened.
+    data class Index(val value: Int, val hardened: Boolean) {
+        /// Returns the string form of this index (e.g. `0'` for a hardened index, `0` otherwise).
+        fun stringRepresentation(): String =
+            value.toString().let { if (hardened) "$it$hardener" else it }
+    }
+
+    companion object {
+        /// Parses a derivation path string (e.g. `m/44'/501'/0'/0'`) into a `DerivePath`, or returns `null` if invalid.
+        fun newInstance(string: String, password: String? = null): DerivePath? {
+            val strings = string.split(separator)
+            if (strings.firstOrNull() != identifier) return null
+            val indexStrings = strings.drop(1)
+
+            val indexes: List<Index> = indexStrings.map { s ->
+                val hardened = s.contains(hardener)
+                val value = s.replace(hardener, "").toIntOrNull() ?: return@map null
+                Index(value, hardened)
+            }.filterNotNull()
+
+            if (indexes.size != indexStrings.count()) return null
+
+            return DerivePath(indexes, password)
+        }
+
+        // Primary      - m/44'/501'/0'/0'
+        //
+        // Incoming     - m/44'/501'/0'/0'/i'/2
+        // Outgoing     - m/44'/501'/0'/0'/i'/3
+        //
+        // Relationship - m/44'/501'/0'/0'/0'/0
+        // Swap         - m/44'/501'/0'/0'/1'/0
+        //
+        // Bucket1      - m/44'/501'/0'/0'/0'/1
+        // Bucket10     - m/44'/501'/0'/0'/0'/10
+        // Bucket100    - m/44'/501'/0'/0'/0'/100
+        // Bucket1k     - m/44'/501'/0'/0'/0'/1000
+        // Bucket10k    - m/44'/501'/0'/0'/0'/10000
+        // Bucket100k   - m/44'/501'/0'/0'/0'/100000
+        // Bucket1m     - m/44'/501'/0'/0'/0'/1000000
+
+        val bucket1    = newInstance("m/44'/501'/0'/0'/0'/1")!!
+        val bucket10   = newInstance("m/44'/501'/0'/0'/0'/10")!!
+        val bucket100  = newInstance("m/44'/501'/0'/0'/0'/100")!!
+        val bucket1k   = newInstance("m/44'/501'/0'/0'/0'/1000")!!
+        val bucket10k  = newInstance("m/44'/501'/0'/0'/0'/10000")!!
+        val bucket100k = newInstance("m/44'/501'/0'/0'/0'/100000")!!
+        val bucket1m   = newInstance("m/44'/501'/0'/0'/0'/1000000")!!
+        val primary    = newInstance("m/44'/501'/0'/0'")!!
+        val swap       = newInstance("m/44'/501'/0'/0'/1'/0")!!
+
+        /// Returns the derivation path for an incoming bucket at the given index.
+        fun getBucketIncoming(index: Int): DerivePath =
+            newInstance("m/44'/501'/0'/0'/$index'/2")!!
+
+        /// Returns the derivation path for an outgoing bucket at the given index.
+        fun getBucketOutgoing(index: Int): DerivePath =
+            newInstance("m/44'/501'/0'/0'/$index'/3")!!
+
+        /// Returns the derivation path for a pool at the given index.
+        fun getPool(index: Long): DerivePath =
+            newInstance("m/44'/501'/0'/0'/7665'/$index'")!!
+
+        /// Returns the derivation path for a pool rendezvous key at the given index.
+        fun getPoolRendezvous(index: Long): DerivePath =
+            newInstance("m/44'/501'/0'/0'/2335'/$index'")!!
+
+        /// Returns the relationship derivation path using the given domain host string as the password.
+        fun relationship(host: String): DerivePath =
+            newInstance("m/44'/501'/0'/0'/0'/0", password = host)!!
+
+        private const val identifier = "m"
+        private const val separator = "/"
+        private const val hardener = "'"
+    }
+}

libs/encryption/mnemonic/src/test/kotlin/com/getcode/crypt/DerivePathTest.kt → libs/encryption/derivepath/src/commonTest/kotlin/com/getcode/crypt/DerivePathTest.kt

@@ -132,5 +132,18 @@ class DerivePathTest {
         assertEquals(a, b)
     }
 
+    @Test
+    fun relationshipUsesHostAsPassword() {
+        val path = DerivePath.relationship("example.com")
+        assertNotNull(path)
+        assertEquals("m/44'/501'/0'/0'/0'/0", path.stringRepresentation())
+        assertEquals("example.com", path.password)
+    }
+
+    @Test
+    fun primaryPathString() {
+        assertEquals("m/44'/501'/0'/0'", DerivePath.primary.stringRepresentation())
+    }
+
     private fun assertFalse(value: Boolean) = kotlin.test.assertFalse(value)
 }

libs/encryption/mnemonic/build.gradle.kts

@@ -9,6 +9,7 @@ android {
 
 dependencies {
     implementation(project(":libs:encryption:base58"))
+    api(project(":libs:encryption:derivepath"))
     implementation(project(":libs:encryption:ed25519"))
     implementation(project(":libs:encryption:hmac"))
     implementation(project(":libs:encryption:sha256"))

libs/encryption/utils/build.gradle.kts

@@ -1,17 +1,44 @@
 plugins {
-    alias(libs.plugins.flipcash.android.library)
+    kotlin("multiplatform")
+    id("com.android.kotlin.multiplatform.library")
 }
 
-android {
-    namespace = "${Gradle.codeNamespace}.encryption.utils"
-}
+kotlin {
+    android {
+        namespace = "com.getcode.encryption.utils"
+        compileSdk = 37
+        minSdk = 29
+        withHostTest {}
+    }
 
-dependencies {
-    implementation(project(":libs:encryption:base58"))
-    implementation(libs.protobuf.kotlin.lite)
-    implementation(project(":libs:encryption:ed25519"))
-    implementation(libs.bundles.kotlinx.serialization)
+    iosArm64()
+    iosSimulatorArm64()
+    iosX64()
 
-    testImplementation(kotlin("test"))
-    testImplementation(libs.robolectric)
+    sourceSets {
+        commonMain {
+            dependencies {
+                implementation(project(":libs:encryption:base58"))
+            }
+        }
+        androidMain {
+            dependencies {
+                implementation(project(":libs:encryption:ed25519"))
+                implementation(project(":libs:logging"))
+                implementation(libs.protobuf.kotlin.lite)
+                implementation(libs.bundles.kotlinx.serialization)
+            }
+        }
+        commonTest {
+            dependencies {
+                implementation(kotlin("test"))
+            }
+        }
+        getByName("androidHostTest") {
+            dependencies {
+                implementation(kotlin("test"))
+                implementation(libs.robolectric)
+            }
+        }
+    }
 }