Android: fix HKDF to pass all RFC5869 test cases

lambdapioneer · Apr 10, 2024 · 11375a8 · 11375a8
1 parent f92cead
commit 11375a8
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Showing 3 changed files with 183 additions and 34 deletions.
diff --git a/android/sloth/src/androidTest/java/com/lambdapioneer/sloth/crypto/HkdfTest.kt b/android/sloth/src/androidTest/java/com/lambdapioneer/sloth/crypto/HkdfTest.kt
@@ -3,36 +3,39 @@ package com.lambdapioneer.sloth.crypto
 import androidx.test.ext.junit.runners.AndroidJUnit4
 import com.lambdapioneer.sloth.utils.decodeAsHex
 import org.assertj.core.api.Assertions.assertThat
-import org.junit.Ignore
 import org.junit.Test
 import org.junit.runner.RunWith
 
 @RunWith(AndroidJUnit4::class)
 class HkdfTest {
 
-    private val instance = Hkdf()
-
     @Test
     fun testDerive_rfc5869_testCase1() {
+        val instance = Hkdf(HmacAlgorithm.SHA256)
+
         val ikm = "0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b".decodeAsHex()
         val salt = "000102030405060708090a0b0c".decodeAsHex()
         val info = "f0f1f2f3f4f5f6f7f8f9".decodeAsHex()
         val l = 42
 
         val actualPrk = instance.extract(salt, ikm)
-        val actualOkm = instance.expand(actualPrk, info, l)
-
         val expectedPrk =
             "077709362c2e32df0ddc3f0dc47bba6390b6c73bb50f9c3122ec844ad7c2b3e5".decodeAsHex()
+        assertThat(actualPrk).isEqualTo(expectedPrk)
+
+        val actualOkm = instance.expand(actualPrk, info, l)
         val expectedOkm =
             "3cb25f25faacd57a90434f64d0362f2a2d2d0a90cf1a5a4c5db02d56ecc4c5bf34007208d5b887185865".decodeAsHex()
-
-        assertThat(actualPrk).isEqualTo(expectedPrk)
         assertThat(actualOkm).isEqualTo(expectedOkm)
+
+        val actualDeriveOutput = instance.derive(salt, ikm, info, l)
+        assertThat(actualDeriveOutput).isEqualTo(expectedOkm)
     }
 
     @Test
     fun testDerive_rfc5869_testCase2() {
+        val instance = Hkdf(HmacAlgorithm.SHA256)
+
         val ikm =
             "000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f202122232425262728292a2b2c2d2e2f303132333435363738393a3b3c3d3e3f404142434445464748494a4b4c4d4e4f".decodeAsHex()
         val salt =
@@ -42,35 +45,168 @@ class HkdfTest {
         val l = 82
 
         val actualPrk = instance.extract(salt, ikm)
-        val actualOkm = instance.expand(actualPrk, info, l)
-
         val expectedPrk =
             "06a6b88c5853361a06104c9ceb35b45cef760014904671014a193f40c15fc244".decodeAsHex()
+        assertThat(actualPrk).isEqualTo(expectedPrk)
+
+        val actualOkm = instance.expand(actualPrk, info, l)
         val expectedOkm =
             "b11e398dc80327a1c8e7f78c596a49344f012eda2d4efad8a050cc4c19afa97c59045a99cac7827271cb41c65e590e09da3275600c2f09b8367793a9aca3db71cc30c58179ec3e87c14c01d5c1f3434f1d87".decodeAsHex()
-
-        assertThat(actualPrk).isEqualTo(expectedPrk)
         assertThat(actualOkm).isEqualTo(expectedOkm)
+
+        val actualDeriveOutput = instance.derive(salt, ikm, info, l)
+        assertThat(actualDeriveOutput).isEqualTo(expectedOkm)
     }
 
     @Test
-    @Ignore("SecretKeySpec complains about 'Empty Key'")
     fun testDerive_rfc5869_testCase3() {
+        val instance = Hkdf(HmacAlgorithm.SHA256)
+
         val ikm = "0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b".decodeAsHex()
         val salt = "".decodeAsHex()
         val info = "".decodeAsHex()
         val l = 42
 
         val actualPrk = instance.extract(salt, ikm)
+        val expectedPrk =
+            "19ef24a32c717b167f33a91d6f648bdf96596776afdb6377ac434c1c293ccb04".decodeAsHex()
+        assertThat(actualPrk).isEqualTo(expectedPrk)
+
         val actualOkm = instance.expand(actualPrk, info, l)
+        val expectedOkm =
+            "8da4e775a563c18f715f802a063c5a31b8a11f5c5ee1879ec3454e5f3c738d2d9d201395faa4b61a96c8".decodeAsHex()
+        assertThat(actualOkm).isEqualTo(expectedOkm)
 
+        val actualDeriveOutput = instance.derive(salt, ikm, info, l)
+        assertThat(actualDeriveOutput).isEqualTo(expectedOkm)
+    }
+
+    @Test
+    fun testDerive_rfc5869_testCase4() {
+        val instance = Hkdf(HmacAlgorithm.SHA256)
+
+        val ikm = "0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b".decodeAsHex()
+        val salt = "".decodeAsHex()
+        val info = "".decodeAsHex()
+        val l = 42
+
+        val actualPrk = instance.extract(salt, ikm)
         val expectedPrk =
             "19ef24a32c717b167f33a91d6f648bdf96596776afdb6377ac434c1c293ccb04".decodeAsHex()
+        assertThat(actualPrk).isEqualTo(expectedPrk)
+
+        val actualOkm = instance.expand(actualPrk, info, l)
         val expectedOkm =
             "8da4e775a563c18f715f802a063c5a31b8a11f5c5ee1879ec3454e5f3c738d2d9d201395faa4b61a96c8".decodeAsHex()
+        assertThat(actualOkm).isEqualTo(expectedOkm)
 
+        val actualDeriveOutput = instance.derive(salt, ikm, info, l)
+        assertThat(actualDeriveOutput).isEqualTo(expectedOkm)
+    }
+
+    @Test
+    fun testDerive_rfc5869_testCase5() {
+        val instance = Hkdf(HmacAlgorithm.SHA1)
+
+        val ikm = "0b0b0b0b0b0b0b0b0b0b0b".decodeAsHex()
+        val salt = "000102030405060708090a0b0c".decodeAsHex()
+        val info = "f0f1f2f3f4f5f6f7f8f9".decodeAsHex()
+        val l = 42
+
+        val actualPrk = instance.extract(salt, ikm)
+        val expectedPrk = "9b6c18c432a7bf8f0e71c8eb88f4b30baa2ba243".decodeAsHex()
         assertThat(actualPrk).isEqualTo(expectedPrk)
+
+        val actualOkm = instance.expand(actualPrk, info, l)
+        val expectedOkm =
+            "085a01ea1b10f36933068b56efa5ad81a4f14b822f5b091568a9cdd4f155fda2c22e422478d305f3f896".decodeAsHex()
         assertThat(actualOkm).isEqualTo(expectedOkm)
+
+        val actualDeriveOutput = instance.derive(salt, ikm, info, l)
+        assertThat(actualDeriveOutput).isEqualTo(expectedOkm)
     }
 
+    @Test
+    fun testDerive_rfc5869_testCase6() {
+        val instance = Hkdf(HmacAlgorithm.SHA1)
+
+        val ikm =
+            "000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f202122232425262728292a2b2c2d2e2f303132333435363738393a3b3c3d3e3f404142434445464748494a4b4c4d4e4f".decodeAsHex()
+        val salt =
+            "606162636465666768696a6b6c6d6e6f707172737475767778797a7b7c7d7e7f808182838485868788898a8b8c8d8e8f909192939495969798999a9b9c9d9e9fa0a1a2a3a4a5a6a7a8a9aaabacadaeaf".decodeAsHex()
+        val info =
+            "b0b1b2b3b4b5b6b7b8b9babbbcbdbebfc0c1c2c3c4c5c6c7c8c9cacbcccdcecfd0d1d2d3d4d5d6d7d8d9dadbdcdddedfe0e1e2e3e4e5e6e7e8e9eaebecedeeeff0f1f2f3f4f5f6f7f8f9fafbfcfdfeff".decodeAsHex()
+        val l = 82
+
+        val actualPrk = instance.extract(salt, ikm)
+        val expectedPrk = "8adae09a2a307059478d309b26c4115a224cfaf6".decodeAsHex()
+        assertThat(actualPrk).isEqualTo(expectedPrk)
+
+        val actualOkm = instance.expand(actualPrk, info, l)
+        val expectedOkm =
+            "0bd770a74d1160f7c9f12cd5912a06ebff6adcae899d92191fe4305673ba2ffe8fa3f1a4e5ad79f3f334b3b202b2173c486ea37ce3d397ed034c7f9dfeb15c5e927336d0441f4c4300e2cff0d0900b52d3b4".decodeAsHex()
+        assertThat(actualOkm).isEqualTo(expectedOkm)
+
+        val actualDeriveOutput = instance.derive(salt, ikm, info, l)
+        assertThat(actualDeriveOutput).isEqualTo(expectedOkm)
+    }
+
+    @Test
+    fun testDerive_rfc5869_testCase7() {
+        val instance = Hkdf(HmacAlgorithm.SHA1)
+
+        val ikm = "0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b".decodeAsHex()
+        val salt = "".decodeAsHex()
+        val info = "".decodeAsHex()
+        val l = 42
+
+        val actualPrk = instance.extract(salt, ikm)
+        val expectedPrk = "da8c8a73c7fa77288ec6f5e7c297786aa0d32d01".decodeAsHex()
+        assertThat(actualPrk).isEqualTo(expectedPrk)
+
+        val actualOkm = instance.expand(actualPrk, info, l)
+        val expectedOkm =
+            "0ac1af7002b3d761d1e55298da9d0506b9ae52057220a306e07b6b87e8df21d0ea00033de03984d34918".decodeAsHex()
+        assertThat(actualOkm).isEqualTo(expectedOkm)
+
+        val actualDeriveOutput = instance.derive(salt, ikm, info, l)
+        assertThat(actualDeriveOutput).isEqualTo(expectedOkm)
+    }
+
+    @Test
+    fun testDerive_rfc5869_testCase8() {
+        val instance = Hkdf(HmacAlgorithm.SHA1)
+
+        val ikm = "0c0c0c0c0c0c0c0c0c0c0c0c0c0c0c0c0c0c0c0c0c0c".decodeAsHex()
+        val salt = null
+        val info = "".decodeAsHex()
+        val l = 42
+
+        val actualPrk = instance.extract(salt, ikm)
+        val expectedPrk = "2adccada18779e7c2077ad2eb19d3f3e731385dd".decodeAsHex()
+        assertThat(actualPrk).isEqualTo(expectedPrk)
+
+        val actualOkm = instance.expand(actualPrk, info, l)
+        val expectedOkm =
+            "2c91117204d745f3500d636a62f64f0ab3bae548aa53d423b0d1f27ebba6f5e5673a081d70cce7acfc48".decodeAsHex()
+        assertThat(actualOkm).isEqualTo(expectedOkm)
+
+        val actualDeriveOutput = instance.derive(salt, ikm, info, l)
+        assertThat(actualDeriveOutput).isEqualTo(expectedOkm)
+    }
+
+    @Test
+    fun testDerive_maxOutputLength() {
+        val hmacAlgorithm = HmacAlgorithm.SHA256
+        val instance = Hkdf(hmacAlgorithm)
+
+        val ikm = "0c0c0c0c0c0c0c0c0c0c0c0c0c0c0c0c0c0c0c0c0c0c".decodeAsHex()
+        val salt = null
+        val info = "".decodeAsHex()
+        val l = 255 * hmacAlgorithm.hashLen
+
+        val actualDeriveOutput = instance.derive(salt, ikm, info, l)
+        assertThat(actualDeriveOutput).hasSize(l)
+
+    }
 }
diff --git a/android/sloth/src/main/java/com/lambdapioneer/sloth/crypto/Hkdf.kt b/android/sloth/src/main/java/com/lambdapioneer/sloth/crypto/Hkdf.kt
@@ -4,54 +4,66 @@ import androidx.annotation.VisibleForTesting
 import com.lambdapioneer.sloth.utils.ceilOfIntegerDivision
 import com.lambdapioneer.sloth.utils.concat
 import java.nio.ByteBuffer
+import java.security.spec.KeySpec
 import javax.crypto.Mac
-import javax.crypto.spec.SecretKeySpec
+import javax.crypto.SecretKey
 
 
-private const val HMAC_SHA256 = "HmacSHA256"
-private const val HMAC_SHA256_LEN = 256 / 8
+internal enum class HmacAlgorithm(val algorithm: String, val hashLen: Int) {
+    SHA256("HmacSHA256", 256 / 8),
+    SHA1("HmacSHA1", 160 / 8),
+}
 
 /**
- * Implementation of the " HMAC-based Extract-and-Expand Key Derivation Function (HKDF)" with
- * support for only SHA-256.
+ * Implementation of the "HMAC-based Extract-and-Expand Key Derivation Function (HKDF)" with
+ * support for SHA-1 and SHA-256.
  *
  * See: https://www.rfc-editor.org/rfc/rfc5869
  */
-internal class Hkdf {
+internal class Hkdf(private val alg: HmacAlgorithm) {
+    private val mac: Mac = Mac.getInstance(alg.algorithm)
 
-    fun derive(salt: ByteArray, ikm: ByteArray, info: ByteArray, l: Int): ByteArray {
+    fun derive(salt: ByteArray?, ikm: ByteArray, info: ByteArray, l: Int): ByteArray {
         val prk = extract(salt = salt, ikm = ikm)
         return expand(prk = prk, info = info, l = l)
     }
 
     @VisibleForTesting
     internal fun extract(salt: ByteArray?, ikm: ByteArray): ByteArray {
-        val saltBytes = salt ?: ByteArray(HMAC_SHA256_LEN)
-        return hmacSha256(saltBytes, ikm)
+        val saltBytes = salt ?: ByteArray(alg.hashLen)
+        return hmac(k = saltBytes, data = ikm)
     }
 
     @VisibleForTesting
     internal fun expand(prk: ByteArray, info: ByteArray, l: Int): ByteArray {
-        // this is ceil(l / HMAC_SHA256_LEN)
-        val iterations = ceilOfIntegerDivision(l, HMAC_SHA256_LEN)
+        // this is ceil(l / hashLen)
+        val iterations = ceilOfIntegerDivision(l, alg.hashLen)
         check(iterations < 256)
 
         var t = ByteArray(0)
-        val buffer = ByteBuffer.allocate(iterations * HMAC_SHA256_LEN)
+        val buffer = ByteBuffer.allocate(iterations * alg.hashLen)
         for (i in 1..iterations) {
-            t = hmacSha256(prk, concat(t, info, byteArrayOf(i.toByte())))
+            t = hmac(k = prk, data = concat(t, info, byteArrayOf(i.toByte())))
             buffer.put(t)
         }
         return buffer.array().sliceArray(0 until l)
     }
 
-    private fun hmacSha256(k: ByteArray, data: ByteArray): ByteArray {
-        // TODO: re-use instance in expand iterations
-        val mac: Mac = Mac.getInstance(HMAC_SHA256)
-
-        // TODO: use custom key spec that allows for an empty key
-        mac.init(SecretKeySpec(k, HMAC_SHA256))
-
-        return mac.doFinal(data)
+    private fun hmac(k: ByteArray, data: ByteArray): ByteArray {
+        mac.init(PermissiveSecretKeySpec(k, alg.algorithm))
+        return mac.doFinal(data) // also resets the instance
     }
 }
+
+/**
+ * Custom KeySpec to allow for empty keys as required by the HKDF spec. Note that an "empty key"
+ * is not the same as "no key".
+ */
+private class PermissiveSecretKeySpec(
+    private val key: ByteArray,
+    private val algorithm: String,
+) : KeySpec, SecretKey {
+    override fun getAlgorithm() = algorithm
+    override fun getFormat() = "RAW"
+    override fun getEncoded() = key
+}
diff --git a/android/sloth/src/main/java/com/lambdapioneer/sloth/impl/LongSlothImpl.kt b/android/sloth/src/main/java/com/lambdapioneer/sloth/impl/LongSlothImpl.kt
@@ -6,6 +6,7 @@ import androidx.annotation.VisibleForTesting
 import com.lambdapioneer.sloth.SlothInconsistentState
 import com.lambdapioneer.sloth.SlothStorageKeyNotFound
 import com.lambdapioneer.sloth.crypto.Hkdf
+import com.lambdapioneer.sloth.crypto.HmacAlgorithm
 import com.lambdapioneer.sloth.crypto.PwHash
 import com.lambdapioneer.sloth.impl.LongSlothKeys.*
 import com.lambdapioneer.sloth.secureelement.KeyHandle
@@ -41,7 +42,7 @@ class LongSlothImpl(
     private val pwHash: PwHash,
     private val tracer: Tracer = NoopTracer(),
 ) {
-    private val hkdf = Hkdf()
+    private val hkdf = Hkdf(HmacAlgorithm.SHA256)
 
     fun onAppStart(storage: WriteableStorage, h: ByteArray) {
         if (exists(storage)) {