fix key agreement on lower android versions for SW keys

a-sit-plus · Jan 14, 2025 · b6a44a9 · b6a44a9
1 parent f77d295
commit b6a44a9
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Showing 4 changed files with 36 additions and 14 deletions.
diff --git a/demoapp/composeApp/src/commonMain/kotlin/at/asitplus/cryptotest/App.kt b/demoapp/composeApp/src/commonMain/kotlin/at/asitplus/cryptotest/App.kt
@@ -54,8 +54,10 @@ import at.asitplus.signum.supreme.sign.makeVerifier
 import at.asitplus.signum.supreme.sign.verify
 import at.asitplus.cryptotest.theme.AppTheme
 import at.asitplus.cryptotest.theme.LocalThemeIsDark
+import at.asitplus.signum.indispensable.CryptoPrivateKey
 import at.asitplus.signum.indispensable.CryptoPublicKey
 import at.asitplus.signum.indispensable.jsonEncoded
+import at.asitplus.signum.supreme.SecretExposure
 import at.asitplus.signum.supreme.agreement.keyAgreement
 import at.asitplus.signum.supreme.asKmmResult
 import at.asitplus.signum.supreme.os.PlatformSignerConfigurationBase
@@ -460,22 +462,37 @@ internal fun App() {
                         Napier.w { "input: $inputData" }
                         Napier.w { "signingKey: $currentKey" }
                         CoroutineScope(context).launch {
-                            val alg= keyAlgorithm.algorithm as SignatureAlgorithm.ECDSA
-                            val eph= Signer.Ephemeral {
-                               ec {
-                                            curve = alg.requiredCurve
-                                                ?: ECCurve.entries.find { it.nativeDigest == alg.digest }!!
-                                            digests = setOf(alg.digest)
+                            val alg = keyAlgorithm.algorithm as SignatureAlgorithm.ECDSA
+                            val eph = Signer.Ephemeral {
+                                ec {
+                                    curve = alg.requiredCurve
+                                        ?: ECCurve.entries.find { it.nativeDigest == alg.digest }!!
+                                    digests = setOf(alg.digest)
 
                                 }
                             }.getOrThrow()
                             val pub = eph.publicKey as CryptoPublicKey.EC
                             Napier.i { "Got Pubkey: $pub" }
-                            val agreed= pub.keyAgreement( currentSigner!!.getOrThrow() as Signer.ECDSA).getOrThrow()
+
+                            val agreed3 =
+                                (currentSigner!!.getOrThrow().publicKey as CryptoPublicKey.EC).keyAgreement(
+                                    @OptIn(SecretExposure::class)
+                                    eph.exportPrivateKey()
+                                        .getOrThrow() as CryptoPrivateKey.WithPublicKey<CryptoPublicKey.EC>
+                                ).getOrThrow()
+                            Napier.i { "AGREED3: ${agreed3.encodeBase64()}" }
+
+
+                            val agreed =
+                                pub.keyAgreement(currentSigner!!.getOrThrow() as Signer.ECDSA)
+                                    .getOrThrow()
                             Napier.i { "AGREED1: ${agreed.encodeBase64()}" }
-                            val agreed2 = ( currentSigner!!.getOrThrow() as Signer.ECDSA).keyAgreement(pub).getOrThrow()
+                            val agreed2 =
+                                (currentSigner!!.getOrThrow() as Signer.ECDSA).keyAgreement(pub)
+                                    .getOrThrow()
                             Napier.i { "AGREED2: ${agreed2.encodeBase64()}" }
-                        }
+
+                             }
 
                     },
 

diff --git a/docs/docs/features.md b/docs/docs/features.md
@@ -52,7 +52,12 @@ from certain (otherwise) hard requirements for Devices launched with later Andro
 Hence, a device launched with Android&nbsp;10, and later updated to Android&nbsp;12 may still not support key agreement in
 hardware.
 The Supreme crypto provider will return a failure, in if key agreement is not supported in hardware.
-TODO: will fail for auth on every use! Bug in Android; fix hidden behind a feature flag
+
+In addition, all Android versions supporting key agreement contain a bug, which makes it impossible
+to perform key agreement using an auth-on-every-use key. The bugfix is hidden behind a disabled-by-default
+feature flag in the Android source code. 
+**Hence, either don't require biometric authentication for key you want to use for key agreement or
+use a timeout of at leas one second!**
 
 ## Supported Algorithms
 

diff --git a/supreme/src/androidMain/kotlin/at/asitplus/signum/supreme/agreement/KeyAgreement.android.kt b/supreme/src/androidMain/kotlin/at/asitplus/signum/supreme/agreement/KeyAgreement.android.kt
@@ -42,7 +42,7 @@ actual suspend fun Signer.ECDSA.performAgreement(
         agreement.doPhase(publicKey.toJcaPublicKey().getOrThrow(), true)
         agreement.generateSecret()
     } else {
-        javax.crypto.KeyAgreement.getInstance("ECDH", "AndroidKeyStore").also {
+        javax.crypto.KeyAgreement.getInstance("ECDH").also {
             @OptIn(HazardousMaterials::class)
             it.init(jcaPrivateKey)
             it.doPhase(publicKey.toJcaPublicKey().getOrThrow(), true)

diff --git a/supreme/src/commonMain/kotlin/at/asitplus/signum/supreme/agreement/KeyAgreement.kt b/supreme/src/commonMain/kotlin/at/asitplus/signum/supreme/agreement/KeyAgreement.kt
@@ -42,12 +42,12 @@ suspend fun CryptoPublicKey.EC.keyAgreement(
  * Elliptic-curve Diffie-Hellman key agreement.
  * Curves of public key and signer need to match!
  */
-suspend fun CryptoPrivateKey.WithPublicKey<CryptoPublicKey.EC>.keyAgreement(publicKey: CryptoPublicKey.EC) = catching {
-    (SignatureAlgorithm.ECDSA(this.publicKey.curve.nativeDigest, this.publicKey.curve).signerFor(this)
+suspend fun CryptoPrivateKey.WithPublicKey<CryptoPublicKey.EC>.keyAgreement(publicKey: CryptoPublicKey.EC) =
+    (SignatureAlgorithm.ECDSA(this.publicKey.curve.nativeDigest, this.publicKey.curve)
+        .signerFor(this)
         .getOrThrow() as Signer.ECDSA).keyAgreement(
         publicKey
     )
-}
 
 /**
  * Elliptic-curve Diffie-Hellman key agreement.