biometricKeysExistAndSignatureValid / return error code with error message

android/src/main/java/com/rnbiometrics/CreateSignatureCallback.java

@@ -30,7 +30,7 @@ public void onAuthenticationError(int errorCode, @NonNull CharSequence errString
             resultMap.putString("error", "User cancellation");
             this.promise.resolve(resultMap);
         } else {
-            this.promise.reject(errString.toString(), errString.toString());
+            this.promise.reject(String.valueOf(errorCode), errString.toString());
         }
     }
 

android/src/main/java/com/rnbiometrics/ReactNativeBiometrics.java

@@ -270,4 +270,32 @@ protected boolean deleteBiometricKey() {
             return false;
         }
     }
+
+    @ReactMethod
+    public void biometricKeysExistAndSignatureValid(Promise promise) {
+        try {
+            boolean doesBiometricKeyExist = doesBiometricKeyExistAndSignatureValid();
+            WritableMap resultMap = new WritableNativeMap();
+            resultMap.putBoolean("keysExist", doesBiometricKeyExist);
+            promise.resolve(resultMap);
+        } catch (Exception e) {
+            promise.reject("Error checking if biometric key exists: " + e.getMessage(),
+                    "Error checking if biometric key exists: " + e.getMessage());
+        }
+    }
+
+    protected boolean doesBiometricKeyExistAndSignatureValid() {
+        try {
+            Signature signature = Signature.getInstance("SHA256withRSA");
+            KeyStore keyStore = KeyStore.getInstance("AndroidKeyStore");
+            keyStore.load(null);
+
+            PrivateKey privateKey = (PrivateKey) keyStore.getKey(biometricKeyAlias, null);
+            signature.initSign(privateKey);
+
+            return true;
+        } catch (Exception e) {
+            return false;
+        }
+    }
 }

index.ts

@@ -51,6 +51,9 @@ interface SimplePromptResult {
   success: boolean
   error?: string
 }
+interface BiometricKeysExistAndSignatureValidResult {
+  keysExist: boolean
+}
 
 /**
  * Enum for touch id sensor type
@@ -132,6 +135,15 @@ export module ReactNativeBiometricsLegacy {
   export function simplePrompt(simplePromptOptions: SimplePromptOptions): Promise<SimplePromptResult> {
     return new ReactNativeBiometrics().simplePrompt(simplePromptOptions)
   }
+
+  /**
+   * Returns promise that resolves to an object with object.keysExists = true | false
+   * indicating if the keys were found to exist or not and signature valid
+   * @returns {Promise<Object>} Promise that resolves to object with details aobut the existence of keys
+   */
+   export function biometricKeysExistAndSignatureValid(): Promise<BiometricKeysExistAndSignatureValidResult> {
+    return new ReactNativeBiometrics().biometricKeysExistAndSignatureValid();
+  }
 }
 
 export default class ReactNativeBiometrics {
@@ -221,4 +233,13 @@ export default class ReactNativeBiometrics {
         ...simplePromptOptions
       })
     }
+
+     /**
+     * Returns promise that resolves to an object with object.keysExists = true | false
+     * indicating if the keys were found to exist or not and signature valid
+     * @returns {Promise<Object>} Promise that resolves to object with details aobut the existence of keys
+     */
+    biometricKeysExistAndSignatureValid(): Promise<BiometricKeysExistAndSignatureValidResult> {
+      return bridge.biometricKeysExistAndSignatureValid();
+    }
   }

ios/ReactNativeBiometrics.m

@@ -223,6 +223,24 @@ @implementation ReactNativeBiometrics
   });
 }
 
+RCT_EXPORT_METHOD(biometricKeysExistAndSignatureValid: (RCTPromiseResolveBlock)resolve rejecter:(RCTPromiseRejectBlock)reject) {
+  dispatch_async(dispatch_get_global_queue( DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
+    BOOL biometricKeyExists = [self doesBiometricKeyExist];
+
+    if (biometricKeyExists) {
+      NSDictionary *result = @{
+        @"keysExist": @(YES)
+      };
+      resolve(result);
+    } else {
+      NSDictionary *result = @{
+        @"keysExist": @(NO)
+      };
+      resolve(result);
+    }
+  });
+}
+
 - (NSData *) getBiometricKeyTag {
   NSString *biometricKeyAlias = @"com.rnbiometrics.biometricKey";
   NSData *biometricKeyTag = [biometricKeyAlias dataUsingEncoding:NSUTF8StringEncoding];