Added support for compact encryption/decryption with caller-provided nonce in SymmetricKey and accompanying tests. Bumped version to 0.9.1-SNAPSHOT.

build.gradle.kts

@@ -20,7 +20,7 @@ plugins {
 }
 
 group = "net.sergeych"
-version = "0.9.0"
+version = "0.9.1-SNAPSHOT"
 
 repositories {
     mavenCentral()

src/commonMain/kotlin/net/sergeych/crypto2/SymmetricKey.kt

@@ -46,13 +46,54 @@ class SymmetricKey(
     data class WithNonce(
         val cipherData: UByteArray,
         val nonce: UByteArray,
-    )
+    ) {
+        override fun equals(other: Any?): Boolean {
+            if (this === other) return true
+            if (other == null || this::class != other::class) return false
+
+            other as WithNonce
+
+            if (!cipherData.contentEquals(other.cipherData)) return false
+            if (!nonce.contentEquals(other.nonce)) return false
+
+            return true
+        }
+
+        override fun hashCode(): Int {
+            var result = cipherData.contentHashCode()
+            result = 31 * result + nonce.contentHashCode()
+            return result
+        }
+    }
 
     override fun encryptWithNonce(plainData: UByteArray, nonce: UByteArray, randomFill: IntRange?): UByteArray {
         require(nonce.size == nonceLength)
         return SecretBox.easy(WithFill.encode(plainData, randomFill), nonce, keyBytes)
     }
 
+    /**
+     * Compact authenticated encryption with a caller-provided nonce.
+     *
+     * This method is meant for storage formats where the nonce is derived or stored elsewhere
+     * and every byte of encoded output matters, for example short encrypted file names.
+     * The output is the raw SecretBox ciphertext only: [plainData] size plus 16 authentication
+     * bytes. The nonce is not stored in the output and must be reproduced exactly for
+     * [decryptCompactWithNonce].
+     *
+     * Unlike [encryptWithNonce], this method does not wrap [plainData] with [WithFill]. For
+     * short payloads this usually saves only 1 byte over [encryptWithNonce], because both
+     * methods already require the caller to manage the nonce separately. Use it only when this
+     * small size gain is important or when the surrounding format explicitly requires raw
+     * SecretBox output.
+     *
+     * Never reuse the same nonce with the same key for different plaintext. Reusing a
+     * `(key, nonce)` pair with SecretBox breaks the security of the stream cipher.
+     */
+    fun encryptCompactWithNonce(plainData: UByteArray, nonce: UByteArray): UByteArray {
+        require(nonce.size == nonceLength)
+        return SecretBox.easy(plainData, nonce, keyBytes)
+    }
+
     override val nonceBytesLength: Int = nonceLength
 
     override val id by lazy {
@@ -64,6 +105,22 @@ class SymmetricKey(
             WithFill.decode(SecretBox.openEasy(cipherData, nonce, keyBytes))
         }
 
+    /**
+     * Compact authenticated decryption with a caller-provided nonce.
+     *
+     * Decrypts data produced by [encryptCompactWithNonce]. The nonce is not read from
+     * [cipherData] and must be the exact same nonce that was used for encryption. Use this
+     * method only for compact formats that intentionally omit both the nonce and the [WithFill]
+     * wrapper.
+     *
+     * @throws DecryptionFailedException if the key, nonce, or cipher data is invalid.
+     */
+    fun decryptCompactWithNonce(cipherData: UByteArray, nonce: UByteArray): UByteArray =
+        protectDecryption {
+            require(nonce.size == nonceLength)
+            SecretBox.openEasy(cipherData, nonce, keyBytes)
+        }
+
     override fun equals(other: Any?): Boolean {
         if (this === other) return true
         if (other !is SymmetricKey) return false
@@ -85,4 +142,4 @@ class SymmetricKey(
         val keyLength = crypto_secretbox_KEYBYTES
     }
 
-}
+}

src/commonTest/kotlin/KeysTest.kt

@@ -11,7 +11,6 @@
 import com.ionspin.kotlin.crypto.util.decodeFromUByteArray
 import com.ionspin.kotlin.crypto.util.encodeToUByteArray
 import kotlinx.coroutines.test.runTest
-import kotlinx.serialization.encodeToString
 import kotlinx.serialization.json.Json
 import net.sergeych.bipack.BipackDecoder
 import net.sergeych.bipack.BipackEncoder
@@ -118,6 +117,44 @@ class KeysTest {
         assertContentEquals(src, k1.decrypt(k1.encrypt(src, 7..117)))
     }
 
+    @Test
+    fun symmetricKeyCompactTest() = runTest {
+        initCrypto()
+        val key = SymmetricKey.new()
+        val otherKey = SymmetricKey.new()
+        val src = "readme.md".encodeToUByteArray()
+        val nonce = key.randomNonce()
+        val cipher = key.encryptCompactWithNonce(src, nonce)
+
+        assertEquals(src.size + 16, cipher.size)
+        assertTrue(cipher.size < key.encryptWithNonce(src, nonce).size)
+        assertTrue(cipher.size < key.encrypt(src).size)
+        assertContentEquals(src, key.decryptCompactWithNonce(cipher, nonce))
+
+        assertThrows<DecryptionFailedException> {
+            otherKey.decryptCompactWithNonce(cipher, nonce)
+        }
+
+        assertThrows<DecryptionFailedException> {
+            val n2 = nonce.copyOf()
+            n2[4] = n2[4].inv()
+            key.decryptCompactWithNonce(cipher, n2)
+        }
+
+        assertThrows<DecryptionFailedException> {
+            val c2 = cipher.copyOf()
+            c2[3] = c2[3].inv()
+            key.decryptCompactWithNonce(c2, nonce)
+        }
+
+        assertThrows<IllegalArgumentException> {
+            key.encryptCompactWithNonce(src, nonce.dropLast(1).toUByteArray())
+        }
+        assertThrows<DecryptionFailedException> {
+            key.decryptCompactWithNonce(cipher, nonce.dropLast(1).toUByteArray())
+        }
+    }
+
     @Test
     fun keyExchangeTest() = runTest {
         initCrypto()