5-improve-encrypted-storage (#6)

Added the use of DEK's for encryption of secrets. Both the KEK's and DEK's are stored in a way that you can have multiple key of which one is active. But the others are still available for decrypting. This allows for implementing key rotation.

Co-authored-by: eelke <eelke@eelkeklein.nl>
Co-authored-by: Eelke76 <31384324+Eelke76@users.noreply.github.com>
Reviewed-on: #6

IdentityShroud.Core/Security/AesGcmHelper.cs

@@ -1,71 +0,0 @@
-using System.Security.Cryptography;
-
-namespace IdentityShroud.Core.Security;
-
-public static class AesGcmHelper
-{
-    
-    public static byte[] EncryptAesGcm(byte[] plaintext, byte[] key)
-    {
-        int tagSize = AesGcm.TagByteSizes.MaxSize;
-        using var aes = new AesGcm(key, tagSize);
-        
-        Span<byte> nonce = stackalloc byte[AesGcm.NonceByteSizes.MaxSize];
-        RandomNumberGenerator.Fill(nonce);
-        Span<byte> ciphertext = stackalloc byte[plaintext.Length];
-        Span<byte> tag = stackalloc byte[tagSize];
-
-        aes.Encrypt(nonce, plaintext, ciphertext, tag);
-
-        // Return concatenated nonce|ciphertext|tag
-        var result = new byte[nonce.Length + ciphertext.Length + tag.Length];
-        nonce.CopyTo(result.AsSpan(0, nonce.Length));
-        ciphertext.CopyTo(result.AsSpan(nonce.Length, ciphertext.Length));
-        tag.CopyTo(result.AsSpan(nonce.Length + ciphertext.Length, tag.Length));
-        return result;
-    }
-    
-    // --------------------------------------------------------------------
-    // DecryptAesGcm
-    //   • key      – 32‑byte (256‑bit) secret key (same key used for encryption)
-    //   • payload  – byte[] containing nonce‖ciphertext‖tag
-    //   • returns  – the original plaintext bytes
-    // --------------------------------------------------------------------
-    public static byte[] DecryptAesGcm(byte[] payload, byte[] key)
-    {
-        if (payload == null) throw new ArgumentNullException(nameof(payload));
-        if (key == null)     throw new ArgumentNullException(nameof(key));
-        if (key.Length != 32) // 256‑bit key
-            throw new ArgumentException("Key must be 256 bits (32 bytes) for AES‑256‑GCM.", nameof(key));
-
-        // ----------------------------------------------------------------
-        // 1️⃣ Extract the three components.
-        // ----------------------------------------------------------------
-        // AesGcm.NonceByteSizes.MaxSize = 12 bytes (standard GCM nonce length)
-        // AesGcm.TagByteSizes.MaxSize   = 16 bytes (128‑bit authentication tag)
-        int nonceSize = AesGcm.NonceByteSizes.MaxSize; // 12
-        int tagSize   = AesGcm.TagByteSizes.MaxSize;   // 16
-
-        if (payload.Length < nonceSize + tagSize)
-            throw new ArgumentException("Payload is too short to contain nonce, ciphertext, and tag.", nameof(payload));
-
-        ReadOnlySpan<byte> nonce = new(payload, 0, nonceSize);
-        ReadOnlySpan<byte> ciphertext = new(payload, nonceSize, payload.Length - nonceSize - tagSize);
-        ReadOnlySpan<byte> tag = new(payload, payload.Length - tagSize, tagSize);
-
-        byte[] plaintext = new byte[ciphertext.Length];
-
-        using var aes = new AesGcm(key, tagSize);
-        try
-        {
-            aes.Decrypt(nonce, ciphertext, tag, plaintext);
-        }
-        catch (CryptographicException ex)
-        {
-            // Tag verification failed → tampering or wrong key/nonce.
-            throw new InvalidOperationException("Decryption failed – authentication tag mismatch.", ex);
-        }
-
-        return plaintext;
-    }
-}

IdentityShroud.Core/Security/ConfigurationSecretProvider.cs

@@ -14,4 +14,9 @@ public class ConfigurationSecretProvider(IConfiguration configuration) : ISecret
     {
         return secrets.GetValue<string>(name) ?? "";
     }
+
+    public KeyEncryptionKey[] GetKeys(string name)
+    {
+        return secrets.GetSection(name).Get<KeyEncryptionKey[]>() ?? [];
+    }
 }

IdentityShroud.Core/Security/DekId.cs

@@ -0,0 +1,6 @@
+namespace IdentityShroud.Core.Security;
+
+public record struct DekId(Guid Id)
+{
+    public static DekId NewId() => new(Guid.NewGuid());
+}

IdentityShroud.Core/Security/EncryptedDek.cs

@@ -0,0 +1,6 @@
+using Microsoft.EntityFrameworkCore;
+
+namespace IdentityShroud.Core.Security;
+
+[Owned]
+public record EncryptedDek(KekId KekId, byte[] Value);

IdentityShroud.Core/Security/EncryptedValue.cs

@@ -0,0 +1,8 @@
+using Microsoft.EntityFrameworkCore;
+
+namespace IdentityShroud.Core.Security;
+
+[Owned]
+public record EncryptedValue(DekId DekId, byte[] Value);
+
+

IdentityShroud.Core/Security/Encryption.cs

@@ -0,0 +1,70 @@
+using System.Security.Cryptography;
+
+namespace IdentityShroud.Core.Security;
+
+public static class Encryption
+{
+    private record struct AlgVersion(int Version, int NonceSize, int TagSize);
+
+    private static AlgVersion[] _versions = 
+    [
+        new(0, 0, 0), // version 0 does not realy exist
+        new(1, 12, 16), // version 1
+    ];
+    
+    public static byte[] Encrypt(ReadOnlySpan<byte> plaintext, ReadOnlySpan<byte> key)
+    {
+        const int versionNumber = 1; 
+        AlgVersion versionParams = _versions[versionNumber];
+
+        int resultSize = 1 + versionParams.NonceSize + versionParams.TagSize + plaintext.Length;
+        // allocate buffer for complete response 
+        var result = new byte[resultSize];
+        
+        result[0] = (byte)versionParams.Version;
+
+        // make the spans that point to the parts of the result where their data is located
+        var nonce = result.AsSpan(1, versionParams.NonceSize); 
+        var tag = result.AsSpan(1 + versionParams.NonceSize, versionParams.TagSize);
+        var cipher = result.AsSpan(1 + versionParams.NonceSize + versionParams.TagSize);
+
+        // use the spans to place the data directly in its place
+        RandomNumberGenerator.Fill(nonce);
+        using var aes = new AesGcm(key, versionParams.TagSize);
+        aes.Encrypt(nonce, plaintext, cipher, tag);
+        return result;
+    }
+    
+    public static byte[] Decrypt(ReadOnlyMemory<byte> input, ReadOnlySpan<byte> key)
+    {
+        var payload = input.Span;
+        int versionNumber = (int)payload[0];
+        if (versionNumber != 1)
+            throw new ArgumentException("Invalid payload");
+        
+        AlgVersion versionParams = _versions[versionNumber];
+        
+        
+        if (payload.Length < 1 + versionParams.NonceSize + versionParams.TagSize)
+            throw new ArgumentException("Payload is too short to contain nonce, ciphertext, and tag.", nameof(payload));
+
+        ReadOnlySpan<byte> nonce = payload.Slice(1, versionParams.NonceSize);
+        ReadOnlySpan<byte> tag = payload.Slice(1 + versionParams.NonceSize, versionParams.TagSize);
+        ReadOnlySpan<byte> cipher = payload.Slice(1 + versionParams.NonceSize + versionParams.TagSize);
+
+        byte[] plaintext = new byte[cipher.Length];
+
+        using var aes = new AesGcm(key, versionParams.TagSize);
+        try
+        {
+            aes.Decrypt(nonce, cipher, tag, plaintext);
+        }
+        catch (CryptographicException ex)
+        {
+            // Tag verification failed → tampering or wrong key/nonce.
+            throw new InvalidOperationException("Decryption failed – authentication tag mismatch.", ex);
+        }
+
+        return plaintext;
+    }
+}

IdentityShroud.Core/Security/JsonWebAlgorithm.cs

@@ -1,5 +1,3 @@
-using System.Security.Cryptography;
-
 namespace IdentityShroud.Core.Security;
 
 public static class JsonWebAlgorithm

IdentityShroud.Core/Security/KekId.cs

@@ -0,0 +1,41 @@
+using System.ComponentModel;
+using System.Globalization;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace IdentityShroud.Core.Security;
+
+[JsonConverter(typeof(KekIdJsonConverter))]
+[TypeConverter(typeof(KekIdTypeConverter))]
+public readonly record struct KekId
+{
+    public Guid Id { get; } 
+
+    public KekId(Guid id)
+    {
+        Id = id;
+    }
+
+    public static KekId NewId()
+    {
+        return new KekId(Guid.NewGuid());
+    }
+}
+
+public class KekIdJsonConverter : JsonConverter<KekId>
+{
+    public override KekId Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+        => new KekId(reader.GetGuid());
+
+    public override void Write(Utf8JsonWriter writer, KekId value, JsonSerializerOptions options)
+        => writer.WriteStringValue(value.Id);
+}
+
+public class KekIdTypeConverter : TypeConverter
+{
+    public override bool CanConvertFrom(ITypeDescriptorContext? context, Type sourceType)
+        => sourceType == typeof(string) || base.CanConvertFrom(context, sourceType);
+
+    public override object? ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object value)
+        => value is string s ? new KekId(Guid.Parse(s)) : base.ConvertFrom(context, culture, value);
+}

IdentityShroud.Core/Security/KeyEncryptionKey.cs

@@ -0,0 +1,10 @@
+namespace IdentityShroud.Core.Security;
+
+/// <summary>
+/// Contains a KEK and associated relevant data. This structure
+/// </summary>
+/// <param name="Id"></param>
+/// <param name="Active"></param>
+/// <param name="Algorithm"></param>
+/// <param name="Key"></param>
+public record KeyEncryptionKey(KekId Id, bool Active, string Algorithm, byte[] Key);

IdentityShroud.Core/Security/Keys/IKeyProvider.cs

@@ -0,0 +1,19 @@
+using IdentityShroud.Core.Messages;
+
+namespace IdentityShroud.Core.Security.Keys;
+
+public abstract class KeyPolicy
+{
+    public abstract string KeyType { get; }
+}
+
+
+public interface IKeyProvider
+{
+    byte[] CreateKey(KeyPolicy policy);
+
+    void SetJwkParameters(byte[] key, JsonWebKey jwk);
+}
+
+
+

IdentityShroud.Core/Security/Keys/IKeyProviderFactory.cs

@@ -0,0 +1,7 @@
+namespace IdentityShroud.Core.Security.Keys;
+
+
+public interface IKeyProviderFactory
+{
+    public IKeyProvider CreateProvider(string keyType);
+}

IdentityShroud.Core/Security/Keys/KeyProviderFactory.cs

@@ -0,0 +1,17 @@
+using IdentityShroud.Core.Security.Keys.Rsa;
+
+namespace IdentityShroud.Core.Security.Keys;
+
+public class KeyProviderFactory : IKeyProviderFactory
+{
+    public IKeyProvider CreateProvider(string keyType)
+    {
+        switch (keyType)
+        {
+            case "RSA":
+                return new RsaProvider();
+            default:
+                throw new NotImplementedException();
+        }
+    }
+}

IdentityShroud.Core/Security/Keys/Rsa/RsaProvider.cs

@@ -0,0 +1,35 @@
+using System.Buffers.Text;
+using System.Security.Cryptography;
+using IdentityShroud.Core.Messages;
+
+namespace IdentityShroud.Core.Security.Keys.Rsa;
+
+public class RsaKeyPolicy : KeyPolicy
+{
+    public override string KeyType => "RSA";
+    public int KeySize { get; } = 2048;
+}
+
+public class RsaProvider : IKeyProvider
+{
+    public byte[] CreateKey(KeyPolicy policy)
+    {
+        if (policy is RsaKeyPolicy p)
+        {
+            using var rsa = RSA.Create(p.KeySize);
+            return rsa.ExportPkcs8PrivateKey();
+        }
+
+        throw new ArgumentException("Incorrect policy type", nameof(policy));
+    }
+
+    public void SetJwkParameters(byte[] key, JsonWebKey jwk)
+    {
+        using var rsa = RSA.Create();
+        rsa.ImportPkcs8PrivateKey(key, out _);
+        var parameters = rsa.ExportParameters(includePrivateParameters: false);
+
+        jwk.Exponent = Base64Url.EncodeToString(parameters.Exponent);
+        jwk.Modulus = Base64Url.EncodeToString(parameters.Modulus);
+    }
+}

IdentityShroud.Core/Security/RsaHelper.cs

@@ -1,16 +0,0 @@
-using System.Security.Cryptography;
-
-namespace IdentityShroud.Core.Security;
-
-public static class RsaHelper
-{
-    /// <summary>
-    /// Load RSA private key from PKCS#8 format
-    /// </summary>
-    public static RSA LoadFromPkcs8(byte[] pkcs8Key)
-    {
-        var rsa = RSA.Create();
-        rsa.ImportPkcs8PrivateKey(pkcs8Key, out _);
-        return rsa;
-    }
-}