From e87e1c57f929708d78d2f9a171d837765f757149 Mon Sep 17 00:00:00 2001
From: max <max.holleman@hotmail.nl>
Date: Thu, 23 Oct 2025 19:45:36 +0200
Subject: [PATCH] [CHANGE] Updated cipher implementation and added decipher
 function

---
 Manager.YouTube/Util/Cipher/CipherDecoder.cs | 40 ++++++++++++++++++--
 Manager.YouTube/Util/Cipher/CipherManager.cs |  2 +-
 2 files changed, 37 insertions(+), 5 deletions(-)

diff --git a/Manager.YouTube/Util/Cipher/CipherDecoder.cs b/Manager.YouTube/Util/Cipher/CipherDecoder.cs
index a61a932..c917354 100644
--- a/Manager.YouTube/Util/Cipher/CipherDecoder.cs
+++ b/Manager.YouTube/Util/Cipher/CipherDecoder.cs
@@ -1,3 +1,4 @@
+using System.Collections.Frozen;
 using System.Text;
 using System.Text.RegularExpressions;
 using Manager.YouTube.Util.Cipher.Operations;
@@ -8,11 +9,11 @@ public partial class CipherDecoder
 {
     public required string Version { get; init; }
     public required string OriginalRelativeUrl { get; init; }
-    public readonly IReadOnlyCollection<ICipherOperation> Operations;
+    public readonly IReadOnlySet<ICipherOperation> Operations;
 
     private CipherDecoder(IEnumerable<ICipherOperation> operations)
     {
-        Operations = operations.ToList();
+        Operations = operations.ToFrozenSet();
         if (Operations.Count == 0)
         {
             throw new ArgumentNullException(nameof(operations), "No decipher operations given.");
@@ -30,6 +31,37 @@ public partial class CipherDecoder
         return decoder;
     }
 
+    public string Decipher(string signatureCipher)
+    {
+        var urlBuilder = new StringBuilder();
+
+        var indexStart = signatureCipher.IndexOf("s=", StringComparison.Ordinal);
+        var indexEnd = signatureCipher.IndexOf("&", StringComparison.Ordinal);
+        var signature = signatureCipher.Substring(indexStart, indexEnd);
+
+        indexStart = signatureCipher.IndexOf("&sp", StringComparison.Ordinal);
+        indexEnd = signatureCipher.IndexOf("&url", StringComparison.Ordinal);
+        var spParam = signatureCipher.Substring(indexStart, indexEnd - indexStart);
+
+        indexStart = signatureCipher.IndexOf("&url", StringComparison.Ordinal);
+        var videoUrl = signatureCipher[indexStart..];
+
+
+        signature = signature[(signature.IndexOf('=') + 1)..];
+        spParam = spParam[(spParam.IndexOf('=') + 1)..];
+        videoUrl = videoUrl[(videoUrl.IndexOf('=') + 1)..];
+        if (string.IsNullOrWhiteSpace(signature))
+        {
+            throw new InvalidOperationException("Invalid signature.");
+        }
+        var signatureDeciphered = Operations.Aggregate(signature, (acc, op) => op.Decipher(acc));
+
+        urlBuilder.Append(videoUrl);
+        urlBuilder.Append($"&{spParam}=");
+        urlBuilder.Append(signatureDeciphered);
+        return urlBuilder.ToString();
+    }
+
     private static async Task<IEnumerable<ICipherOperation>> GetCipherOperations(string relativeUrl, YouTubeClient? client = null)
     {
         var downloadRequest = new HttpRequestMessage(HttpMethod.Get, new Uri($"{NetworkService.Origin}/{relativeUrl}"));
@@ -49,7 +81,7 @@ public partial class CipherDecoder
         var definitionBody = DefinitionBodyRegex().Match(functionBody).Groups[1].Value;
         var decipherDefinition = Regex.Match(playerJs, $@"var\s+{definitionBody}=\{{(\w+:function\(\w+(,\w+)?\)\{{(.*?)\}}),?\}};", RegexOptions.Singleline).Groups[0].ToString();
 
-        List<ICipherOperation> operations = [];
+        SortedSet<ICipherOperation> operations = [];
         foreach (var statement in functionBody.Split(';'))
         {
             // Get the name of the function called in this statement
@@ -73,7 +105,7 @@ public partial class CipherDecoder
             }
         }
 
-        return [];
+        return operations;
     }
 
     
diff --git a/Manager.YouTube/Util/Cipher/CipherManager.cs b/Manager.YouTube/Util/Cipher/CipherManager.cs
index fb06919..9900788 100644
--- a/Manager.YouTube/Util/Cipher/CipherManager.cs
+++ b/Manager.YouTube/Util/Cipher/CipherManager.cs
@@ -8,7 +8,7 @@ public static class CipherManager
     private static readonly CipherDecoderCollection LoadedCiphers = [];
     private static readonly ILogger Logger = LogService.RegisterLogger(typeof(CipherManager));
 
-    public static async Task<Result<CipherDecoder>> GetDecoder(YouTubeClient client)
+    public static async Task<Result<CipherDecoder>> GetDecoderAsync(YouTubeClient client)
     {
         var relativePlayerJsUrl = client.State?.PlayerJsUrl;
         if (string.IsNullOrEmpty(relativePlayerJsUrl))