Trusted entitlements: Use new signature verification format (#1111)

### Description
Third PR for SDK-3200

- Adds support to the new signature format (salt + nonce + TS + etag +
content)
- Adds support for intermediate signatures verification
- Makes nonce optional in preparation of static endpoint signing.

Based on #1109 and #1110.

purchases/src/main/kotlin/com/revenuecat/purchases/common/HTTPClient.kt

@@ -175,10 +175,9 @@ internal class HTTPClient(
         }
 
         val verificationResult = if (shouldSignResponse &&
-            nonce != null &&
             RCHTTPStatusCodes.isSuccessful(responseCode)
         ) {
-            verifyResponse(path, responseCode, connection, payload, nonce)
+            verifyResponse(path, connection, payload, nonce)
         } else {
             VerificationResult.NOT_REQUESTED
         }
@@ -278,15 +277,13 @@ internal class HTTPClient(
 
     private fun verifyResponse(
         urlPath: String,
-        responseCode: Int,
         connection: URLConnection,
         payload: String?,
-        nonce: String,
+        nonce: String?,
     ): VerificationResult {
         return signingManager.verifyResponse(
             urlPath = urlPath,
-            responseCode = responseCode,
-            signature = connection.getHeaderField(HTTPResult.SIGNATURE_HEADER_NAME),
+            signatureString = connection.getHeaderField(HTTPResult.SIGNATURE_HEADER_NAME),
             nonce = nonce,
             body = payload,
             requestTime = getRequestTimeHeader(connection),

purchases/src/main/kotlin/com/revenuecat/purchases/common/verification/SignatureVerificationMode.kt

@@ -6,21 +6,29 @@ internal sealed class SignatureVerificationMode {
     companion object {
         fun fromEntitlementVerificationMode(
             verificationMode: EntitlementVerificationMode,
-            signatureVerifier: SignatureVerifier? = null,
+            rootVerifier: SignatureVerifier? = null,
         ): SignatureVerificationMode {
             return when (verificationMode) {
                 EntitlementVerificationMode.DISABLED -> Disabled
                 EntitlementVerificationMode.INFORMATIONAL ->
-                    Informational(signatureVerifier ?: DefaultSignatureVerifier())
+                    Informational(IntermediateSignatureHelper(rootVerifier ?: DefaultSignatureVerifier()))
                 // Hidden ENFORCED mode during feature beta
                 // EntitlementVerificationMode.ENFORCED ->
                 //     Enforced(signatureVerifier ?: DefaultSignatureVerifier())
             }
         }
+
+        private fun createIntermediateSignatureHelper(): IntermediateSignatureHelper {
+            return IntermediateSignatureHelper(DefaultSignatureVerifier())
+        }
     }
     object Disabled : SignatureVerificationMode()
-    data class Informational(val signatureVerifier: SignatureVerifier) : SignatureVerificationMode()
-    data class Enforced(val signatureVerifier: SignatureVerifier) : SignatureVerificationMode()
+    data class Informational(
+        override val intermediateSignatureHelper: IntermediateSignatureHelper = createIntermediateSignatureHelper(),
+    ) : SignatureVerificationMode()
+    data class Enforced(
+        override val intermediateSignatureHelper: IntermediateSignatureHelper = createIntermediateSignatureHelper(),
+    ) : SignatureVerificationMode()
 
     val shouldVerify: Boolean
         get() = when (this) {
@@ -32,10 +40,10 @@ internal sealed class SignatureVerificationMode {
                 true
         }
 
-    val verifier: SignatureVerifier?
+    open val intermediateSignatureHelper: IntermediateSignatureHelper?
         get() = when (this) {
             is Disabled -> null
-            is Informational -> signatureVerifier
-            is Enforced -> signatureVerifier
+            is Informational -> intermediateSignatureHelper
+            is Enforced -> intermediateSignatureHelper
         }
 }

purchases/src/main/kotlin/com/revenuecat/purchases/common/verification/SigningManager.kt

@@ -5,9 +5,9 @@ import com.revenuecat.purchases.VerificationResult
 import com.revenuecat.purchases.common.AppConfig
 import com.revenuecat.purchases.common.errorLog
 import com.revenuecat.purchases.common.networking.Endpoint
-import com.revenuecat.purchases.common.networking.RCHTTPStatusCodes
 import com.revenuecat.purchases.common.warnLog
 import com.revenuecat.purchases.strings.NetworkStrings
+import com.revenuecat.purchases.utils.Result
 import java.security.SecureRandom
 
 internal class SigningManager(
@@ -16,7 +16,6 @@ internal class SigningManager(
 ) {
     private companion object {
         const val NONCE_BYTES_SIZE = 12
-        const val SALT_BYTES_SIZE = 16
     }
 
     fun shouldVerifyEndpoint(endpoint: Endpoint): Boolean {
@@ -29,12 +28,11 @@ internal class SigningManager(
         return String(Base64.encode(bytes, Base64.DEFAULT))
     }
 
-    @Suppress("LongParameterList", "ReturnCount")
+    @Suppress("LongParameterList", "ReturnCount", "CyclomaticComplexMethod")
     fun verifyResponse(
         urlPath: String,
-        responseCode: Int,
-        signature: String?,
-        nonce: String,
+        signatureString: String?,
+        nonce: String?,
         body: String?,
         requestTime: String?,
         eTag: String?,
@@ -43,39 +41,56 @@ internal class SigningManager(
             warnLog("Forcing signing error for request with path: $urlPath")
             return VerificationResult.FAILED
         }
-        val signatureVerifier = signatureVerificationMode.verifier ?: return VerificationResult.NOT_REQUESTED
+        val intermediateSignatureHelper = signatureVerificationMode.intermediateSignatureHelper
+            ?: return VerificationResult.NOT_REQUESTED
 
-        if (signature == null) {
+        if (signatureString == null) {
             errorLog(NetworkStrings.VERIFICATION_MISSING_SIGNATURE.format(urlPath))
             return VerificationResult.FAILED
         }
         if (requestTime == null) {
             errorLog(NetworkStrings.VERIFICATION_MISSING_REQUEST_TIME.format(urlPath))
             return VerificationResult.FAILED
         }
-
-        val signatureMessage = getSignatureMessage(responseCode, body, eTag)
-        if (signatureMessage == null) {
+        if (body == null && eTag == null) {
             errorLog(NetworkStrings.VERIFICATION_MISSING_BODY_OR_ETAG.format(urlPath))
             return VerificationResult.FAILED
         }
 
-        val decodedNonce = Base64.decode(nonce, Base64.DEFAULT)
-        val decodedSignature = Base64.decode(signature, Base64.DEFAULT)
-        val saltBytes = decodedSignature.copyOfRange(0, SALT_BYTES_SIZE)
-        val signatureToVerify = decodedSignature.copyOfRange(SALT_BYTES_SIZE, decodedSignature.size)
-        val messageToVerify = saltBytes + decodedNonce + requestTime.toByteArray() + signatureMessage.toByteArray()
-        val verificationResult = signatureVerifier.verify(signatureToVerify, messageToVerify)
-
-        return if (verificationResult) {
-            VerificationResult.VERIFIED
-        } else {
-            errorLog(NetworkStrings.VERIFICATION_ERROR.format(urlPath))
-            VerificationResult.FAILED
+        val signature: Signature
+        try {
+            signature = Signature.fromString(signatureString)
+        } catch (e: InvalidSignatureSizeException) {
+            errorLog(NetworkStrings.VERIFICATION_INVALID_SIZE.format(urlPath, e.message))
+            return VerificationResult.FAILED
         }
-    }
 
-    private fun getSignatureMessage(responseCode: Int, body: String?, eTag: String?): String? {
-        return if (responseCode == RCHTTPStatusCodes.NOT_MODIFIED) eTag else body
+        when (val result = intermediateSignatureHelper.createIntermediateKeyVerifierIfVerified(signature)) {
+            is Result.Error -> {
+                errorLog(
+                    NetworkStrings.VERIFICATION_INTERMEDIATE_KEY_FAILED.format(
+                        urlPath,
+                        result.value.underlyingErrorMessage,
+                    ),
+                )
+                return VerificationResult.FAILED
+            }
+            is Result.Success -> {
+                val intermediateKeyVerifier = result.value
+                val decodedNonce = nonce?.let { Base64.decode(it, Base64.DEFAULT) } ?: byteArrayOf()
+                val requestTimeBytes = requestTime.toByteArray()
+                val eTagBytes = eTag?.toByteArray() ?: byteArrayOf()
+                val payloadBytes = body?.toByteArray() ?: byteArrayOf()
+                val messageToVerify = signature.salt + decodedNonce + requestTimeBytes + eTagBytes + payloadBytes
+                val verificationResult = intermediateKeyVerifier.verify(signature.payload, messageToVerify)
+
+                return if (verificationResult) {
+                    VerificationResult.VERIFIED
+                } else {
+                    errorLog(NetworkStrings.VERIFICATION_ERROR.format(urlPath))
+                    VerificationResult.FAILED
+                }
+            }
+        }
     }
 }

purchases/src/main/kotlin/com/revenuecat/purchases/strings/NetworkStrings.kt

@@ -11,9 +11,12 @@ internal object NetworkStrings {
     const val SAME_CALL_ALREADY_IN_PROGRESS = "Same call already in progress, adding to callbacks map with key: %s"
     const val PROBLEM_CONNECTING = "Unable to start a network connection due to a network configuration issue: %s"
     const val VERIFICATION_MISSING_SIGNATURE = "Verification: Request to '%s' requires a signature but none provided."
+    const val VERIFICATION_INTERMEDIATE_KEY_FAILED = "Verification: Request to '%s' provided an intermediate key that" +
+        " did not verify correctly. Reason %s"
     const val VERIFICATION_MISSING_REQUEST_TIME = "Verification: Request to '%s' requires a request time" +
         " but none provided."
     const val VERIFICATION_MISSING_BODY_OR_ETAG = "Verification: Request to '%s' requires a body or etag" +
         " but none provided."
+    const val VERIFICATION_INVALID_SIZE = "Verification: Request to '%s' has signature with wrong size. '%s'"
     const val VERIFICATION_ERROR = "Verification: Request to '%s' failed verification."
 }

purchases/src/test/java/com/revenuecat/purchases/common/HTTPClientVerificationTest.kt

@@ -41,7 +41,7 @@ internal class HTTPClientVerificationTest: BaseHTTPClientTest() {
         )
 
         every {
-            mockSigningManager.verifyResponse(any(), any(), any(), any(), any(), any(), any())
+            mockSigningManager.verifyResponse(any(), any(), any(), any(), any(), any())
         } returns VerificationResult.VERIFIED
 
         client.performRequest(
@@ -81,7 +81,7 @@ internal class HTTPClientVerificationTest: BaseHTTPClientTest() {
 
         assertThat(result.verificationResult).isEqualTo(VerificationResult.NOT_REQUESTED)
         verify(exactly = 0) {
-            mockSigningManager.verifyResponse(any(), any(), any(), any(), any(), any(), any())
+            mockSigningManager.verifyResponse(any(), any(), any(), any(), any(), any())
         }
     }
 
@@ -112,7 +112,7 @@ internal class HTTPClientVerificationTest: BaseHTTPClientTest() {
 
         assertThat(result.verificationResult).isEqualTo(VerificationResult.NOT_REQUESTED)
         verify(exactly = 0) {
-            mockSigningManager.verifyResponse(any(), any(), any(), any(), any(), any(), any())
+            mockSigningManager.verifyResponse(any(), any(), any(), any(), any(), any())
         }
     }
 
@@ -143,7 +143,7 @@ internal class HTTPClientVerificationTest: BaseHTTPClientTest() {
 
         assertThat(result.verificationResult).isEqualTo(VerificationResult.NOT_REQUESTED)
         verify(exactly = 0) {
-            mockSigningManager.verifyResponse(any(), any(), any(), any(), any(), any(), any())
+            mockSigningManager.verifyResponse(any(), any(), any(), any(), any(), any())
         }
     }
 
@@ -157,7 +157,7 @@ internal class HTTPClientVerificationTest: BaseHTTPClientTest() {
         val responseCode = expectedResult.responseCode
 
         every {
-            mockSigningManager.verifyResponse(any(), any(), any(), any(), any(), any(), any())
+            mockSigningManager.verifyResponse(any(), any(), any(), any(), any(), any())
         } returns VerificationResult.VERIFIED
 
         every {
@@ -192,7 +192,6 @@ internal class HTTPClientVerificationTest: BaseHTTPClientTest() {
         verify(exactly = 1) {
             mockSigningManager.verifyResponse(
                 endpoint.getPath(),
-                responseCode,
                 "test-signature",
                 "test-nonce",
                 "{\"test-key\":\"test-value\"}",
@@ -222,7 +221,7 @@ internal class HTTPClientVerificationTest: BaseHTTPClientTest() {
         server.takeRequest()
         assertThat(result.verificationResult).isEqualTo(VerificationResult.NOT_REQUESTED)
         verify(exactly = 0) {
-            mockSigningManager.verifyResponse(any(), any(), any(), any(), any(), any(), any())
+            mockSigningManager.verifyResponse(any(), any(), any(), any(), any(), any())
         }
     }
 
@@ -236,7 +235,7 @@ internal class HTTPClientVerificationTest: BaseHTTPClientTest() {
         )
 
         every {
-            mockSigningManager.verifyResponse(any(), any(), any(), any(), any(), any(), any())
+            mockSigningManager.verifyResponse(any(), any(), any(), any(), any(), any())
         } returns VerificationResult.FAILED
 
         val result = client.performRequest(
@@ -261,7 +260,7 @@ internal class HTTPClientVerificationTest: BaseHTTPClientTest() {
         )
 
         every {
-            mockSigningManager.verifyResponse(any(), any(), any(), any(), any(), any(), any())
+            mockSigningManager.verifyResponse(any(), any(), any(), any(), any(), any())
         } returns VerificationResult.FAILED
 
         var thrownCorrectException = false
@@ -292,7 +291,7 @@ internal class HTTPClientVerificationTest: BaseHTTPClientTest() {
         )
 
         every {
-            mockSigningManager.verifyResponse(any(), any(), any(), any(), any(), any(), any())
+            mockSigningManager.verifyResponse(any(), any(), any(), any(), any(), any())
         } returns VerificationResult.VERIFIED
 
         val result = client.performRequest(

purchases/src/test/java/com/revenuecat/purchases/common/verification/SignatureVerificationModeTest.kt

@@ -27,9 +27,18 @@ class SignatureVerificationModeTest {
 
     @Test
     fun `shouldVerify has correct values for all the verification modes`() {
-        val signatureVerifier = DefaultSignatureVerifier()
         assertThat(SignatureVerificationMode.Disabled.shouldVerify).isFalse
-        assertThat(SignatureVerificationMode.Informational(signatureVerifier).shouldVerify).isTrue
-        assertThat(SignatureVerificationMode.Enforced(signatureVerifier).shouldVerify).isTrue
+        assertThat(SignatureVerificationMode.Informational().shouldVerify).isTrue
+        assertThat(SignatureVerificationMode.Enforced().shouldVerify).isTrue
+    }
+
+    @Test
+    fun `intermediateSignatureHelper has values in enabled verification modes`() {
+        var verificationMode: SignatureVerificationMode = SignatureVerificationMode.Disabled
+        assertThat(verificationMode.intermediateSignatureHelper).isNull()
+        verificationMode = SignatureVerificationMode.Informational()
+        assertThat(verificationMode.intermediateSignatureHelper).isNotNull
+        verificationMode = SignatureVerificationMode.Enforced()
+        assertThat(verificationMode.intermediateSignatureHelper).isNotNull
     }
 }