Fix getCiphertextPath for Windows again.

src/main/java/org/cryptomator/common/vaults/Vault.java

@@ -316,18 +316,29 @@ public class Vault {
 
 	/**
 	 * Gets from the cleartext path its ciphertext counterpart.
-	 * The cleartext path has to start from the vault root (by starting with "/").
 	 *
 	 * @return Local os path to the ciphertext resource
 	 * @throws IOException if an I/O error occurs
+	 * @throws IllegalStateException if the vault is not unlocked
 	 */
-	public Path getCiphertextPath(String cleartextPath) throws IOException {
-		if (!cleartextPath.startsWith("/")) {
-			throw new IllegalArgumentException("Input path must be absolute from vault root by starting with \"/\".");
+	public Path getCiphertextPath(Path cleartextPath) throws IOException {
+		if (!state.getValue().equals(VaultState.Value.UNLOCKED)) {
+			throw new IllegalStateException("Vault is not unlocked");
 		}
 		var fs = cryptoFileSystem.get();
-		var cryptoPath = fs.getPath(cleartextPath);
-		return fs.getCiphertextPath(cryptoPath);
+		var osPathSeparator = cleartextPath.getFileSystem().getSeparator();
+		var cryptoFsPathSeparator = fs.getSeparator();
+
+		if (getMountPoint() instanceof Mountpoint.WithPath mp) {
+			var absoluteCryptoFsPath = cryptoFsPathSeparator + mp.path().relativize(cleartextPath).toString();
+			if (!cryptoFsPathSeparator.equals(osPathSeparator)) {
+				absoluteCryptoFsPath = absoluteCryptoFsPath.replace(osPathSeparator, cryptoFsPathSeparator);
+			}
+			var cryptoPath = fs.getPath(absoluteCryptoFsPath);
+			return fs.getCiphertextPath(cryptoPath);
+		} else {
+			throw new UnsupportedOperationException("URI mount points not supported.");
+		}
 	}
 
 	public VaultConfigCache getVaultConfigCache() {

src/main/java/org/cryptomator/ui/mainwindow/VaultDetailUnlockedController.java

@@ -166,12 +166,7 @@ public class VaultDetailUnlockedController implements FxController {
 			return Optional.empty();
 		}
 		try {
-			var accessPoint = mountPoint.getValue();
-			var cleartextPath = path.toString().substring(accessPoint.length());
-			if (!cleartextPath.startsWith("/")) {
-				cleartextPath = "/" + cleartextPath;
-			}
-			return Optional.of(vault.get().getCiphertextPath(cleartextPath));
+			return Optional.of(vault.get().getCiphertextPath(path));
 		} catch (IOException e) {
 			LOG.warn("Unable to get ciphertext path from path: {}", path, e);
 			return Optional.empty();