From 8175af4e844474bb8139a546776013d281e86ded Mon Sep 17 00:00:00 2001
From: Kyle Spearrin <kyle.spearrin@gmail.com>
Date: Thu, 29 Nov 2018 17:10:51 -0500
Subject: [PATCH] add steam support for otp generation

---
 src/App/Models/OtpAuth.cs   |  7 +++++++
 src/App/Utilities/Crypto.cs | 20 ++++++++++++++++++--
 2 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/src/App/Models/OtpAuth.cs b/src/App/Models/OtpAuth.cs
index 01f2e0b5d..971587788 100644
--- a/src/App/Models/OtpAuth.cs
+++ b/src/App/Models/OtpAuth.cs
@@ -44,6 +44,12 @@ namespace Bit.App.Models
                     }
                 }
             }
+            else if (key?.ToLowerInvariant().StartsWith("steam://") ?? false)
+            {
+                Steam = true;
+                Digits = 5;
+                Secret = key.Substring(8);
+            }
             else
             {
                 Secret = key;
@@ -54,5 +60,6 @@ namespace Bit.App.Models
         public int Digits { get; set; } = 6;
         public MacAlgorithm Algorithm { get; set; } = MacAlgorithm.HmacSha1;
         public string Secret { get; set; }
+        public bool Steam { get; set; }
     }
 }
diff --git a/src/App/Utilities/Crypto.cs b/src/App/Utilities/Crypto.cs
index 3e2b748cc..81dc30fd5 100644
--- a/src/App/Utilities/Crypto.cs
+++ b/src/App/Utilities/Crypto.cs
@@ -9,6 +9,8 @@ namespace Bit.App.Utilities
 {
     public static class Crypto
     {
+        private static string SteamChars = "23456789BCDFGHJKMNPQRTVWXY";
+
         public static CipherString AesCbcEncrypt(byte[] plainBytes, SymmetricCryptoKey key)
         {
             var parts = AesCbcEncryptToParts(plainBytes, key);
@@ -203,9 +205,23 @@ namespace Bit.App.Utilities
             var offset = (hash[hash.Length - 1] & 0xf);
             var binary = ((hash[offset] & 0x7f) << 24) | ((hash[offset + 1] & 0xff) << 16) |
                 ((hash[offset + 2] & 0xff) << 8) | (hash[offset + 3] & 0xff);
-            var otp = binary % (int)Math.Pow(10, otpParams.Digits);
 
-            return otp.ToString().PadLeft(otpParams.Digits, '0');
+            string otp = string.Empty;
+            if(otpParams.Steam)
+            {
+                var fullCode = binary & 0x7fffffff;
+                for(var i = 0; i < otpParams.Digits; i++)
+                {
+                    otp += SteamChars[fullCode % SteamChars.Length];
+                    fullCode = (int)Math.Truncate(fullCode / (double)SteamChars.Length);
+                }
+            }
+            else
+            {
+                var rawOtp = binary % (int)Math.Pow(10, otpParams.Digits);
+                otp = rawOtp.ToString().PadLeft(otpParams.Digits, '0');
+            }
+            return otp;
         }
 
         // ref: https://tools.ietf.org/html/rfc5869