remade into 1 project

RelayCore/E2EeHelper.cs

@@ -0,0 +1,82 @@
+using System.Security.Cryptography;
+using System.Text;
+
+namespace RelayCore;
+
+public static class E2EeHelper
+{
+    public static (string publicKey, string privateKey) GenerateRsaKeyPair()
+    {
+        using var rsa = RSA.Create(2048);
+
+        var publicKey = Convert.ToBase64String(rsa.ExportSubjectPublicKeyInfo());
+        var privateKey = Convert.ToBase64String(rsa.ExportPkcs8PrivateKey());
+
+        return (publicKey, privateKey);
+    }
+
+    public static EncryptedMessagePayload EncryptForRecipient(string plainText, string recipientPublicKeyBase64)
+    {
+        var aesKey = RandomNumberGenerator.GetBytes(32);
+        var nonce = RandomNumberGenerator.GetBytes(12);
+        var plainBytes = Encoding.UTF8.GetBytes(plainText);
+        var cipherBytes = new byte[plainBytes.Length];
+        var tag = new byte[16];
+
+        using (var aes = new AesGcm(aesKey, 16))
+        {
+            aes.Encrypt(nonce, plainBytes, cipherBytes, tag);
+        }
+
+        var recipientPublicKey = Convert.FromBase64String(recipientPublicKeyBase64);
+        byte[] encryptedKey;
+
+        using (var rsa = RSA.Create())
+        {
+            rsa.ImportSubjectPublicKeyInfo(recipientPublicKey, out _);
+            encryptedKey = rsa.Encrypt(aesKey, RSAEncryptionPadding.OaepSHA256);
+        }
+
+        return new EncryptedMessagePayload
+        {
+            CipherText = Convert.ToBase64String(cipherBytes),
+            Nonce = Convert.ToBase64String(nonce),
+            Tag = Convert.ToBase64String(tag),
+            EncryptedKey = Convert.ToBase64String(encryptedKey)
+        };
+    }
+
+    public static string DecryptForRecipient(EncryptedMessagePayload payload, string recipientPrivateKeyBase64)
+    {
+        var encryptedKey = Convert.FromBase64String(payload.EncryptedKey);
+        var privateKey = Convert.FromBase64String(recipientPrivateKeyBase64);
+
+        byte[] aesKey;
+
+        using (var rsa = RSA.Create())
+        {
+            rsa.ImportPkcs8PrivateKey(privateKey, out _);
+            aesKey = rsa.Decrypt(encryptedKey, RSAEncryptionPadding.OaepSHA256);
+        }
+
+        var nonce = Convert.FromBase64String(payload.Nonce);
+        var tag = Convert.FromBase64String(payload.Tag);
+        var cipherBytes = Convert.FromBase64String(payload.CipherText);
+        var plainBytes = new byte[cipherBytes.Length];
+
+        using (var aes = new AesGcm(aesKey, 16))
+        {
+            aes.Decrypt(nonce, cipherBytes, tag, plainBytes);
+        }
+
+        return Encoding.UTF8.GetString(plainBytes);
+    }
+}
+
+public class EncryptedMessagePayload
+{
+    public required string CipherText { get; set; }
+    public required string Nonce { get; set; }
+    public required string Tag { get; set; }
+    public required string EncryptedKey { get; set; }
+}