[WIP]: Managed HPKE

docs/project/list-of-diagnostics.md

@@ -333,3 +333,4 @@ Diagnostic id values for experimental APIs must not be recycled, as that could s
 |  __`SYSLIB5006`__ |    .NET 10 |     TBD | Types for Post-Quantum Cryptography (PQC) are experimental. |
 |  __`SYSLIB5007`__ |    .NET 11 |     TBD | Low-level TLS engine types (`TlsContext`, `TlsSession`) in `System.Net.Security` are experimental. |
 |  __`SYSLIB5008`__ |    .NET 11 |     TBD | `SocketsHttpHandler` connection eviction control and `HttpRequestMessage.ConnectionId` APIs are experimental. |
+|  __`SYSLIB5009`__ |    .NET 11 |     TBD | Types for HPKE (Hybrid Public Key Encryption) are experimental. |

src/libraries/Common/src/System/Experimentals.cs

@@ -39,6 +39,9 @@ internal static class Experimentals
         // SocketsHttpHandler connection eviction control and HttpRequestMessage.ConnectionId APIs are experimental.
         internal const string SocketsHttpHandlerExperimentalDiagId = "SYSLIB5008";
 
+        // Types for HPKE (Hybrid Public Key Encryption) are experimental.
+        internal const string HpkeExperimentalDiagId = "SYSLIB5009";
+
         // When adding a new diagnostic ID, add it to the table in docs\project\list-of-diagnostics.md as well.
         // Keep new const identifiers above this comment.
     }

src/libraries/Common/src/System/Security/Cryptography/HpkeAead.cs

@@ -0,0 +1,30 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Diagnostics.CodeAnalysis;
+
+namespace System.Security.Cryptography
+{
+    /// <summary>
+    ///   Specifies an authenticated encryption with associated data (AEAD) algorithm for an HPKE cipher suite.
+    /// </summary>
+    /// <seealso cref="HpkeSuite" />
+    [Experimental(Experimentals.HpkeExperimentalDiagId, UrlFormat = Experimentals.SharedUrlFormat)]
+    public enum HpkeAead
+    {
+        /// <summary>
+        ///   Indicates that authenticated encryption uses AES-GCM with a 128-bit key.
+        /// </summary>
+        AES_128_GCM = 1,
+
+        /// <summary>
+        ///   Indicates that authenticated encryption uses AES-GCM with a 256-bit key.
+        /// </summary>
+        AES_256_GCM = 2,
+
+        /// <summary>
+        ///   Indicates that authenticated encryption uses ChaCha20-Poly1305.
+        /// </summary>
+        ChaCha20Poly1305 = 3,
+    }
+}

src/libraries/Common/src/System/Security/Cryptography/HpkeAeadMetadata.cs

@@ -0,0 +1,39 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+namespace System.Security.Cryptography
+{
+    internal sealed partial class HpkeAeadMetadata
+    {
+        internal HpkeAead Aead { get; }
+        internal int Nk { get; }
+        internal int Nn { get; }
+        internal int Nt { get; }
+        internal string Name { get; }
+
+        private HpkeAeadMetadata(HpkeAead aead, int nk, int nn, int nt, string name)
+        {
+            Aead = aead;
+            Nk = nk;
+            Nn = nn;
+            Nt = nt;
+            Name = name;
+        }
+
+        internal static HpkeAeadMetadata? Create(HpkeAead aead)
+        {
+            // https://datatracker.ietf.org/doc/html/draft-ietf-hpke-hpke-04#section-7.3
+            switch (aead)
+            {
+                case HpkeAead.AES_128_GCM:
+                    return new HpkeAeadMetadata(aead, nk: 16, nn: 12, nt: 16, name: "AES-128-GCM");
+                case HpkeAead.AES_256_GCM:
+                    return new HpkeAeadMetadata(aead, nk: 32, nn: 12, nt: 16, name: "AES-256-GCM");
+                case HpkeAead.ChaCha20Poly1305:
+                    return new HpkeAeadMetadata(aead, nk: 32, nn: 12, nt: 16, name: "ChaCha20Poly1305");
+                default:
+                    return null;
+            }
+        }
+    }
+}

src/libraries/Common/src/System/Security/Cryptography/HpkeKdf.cs

@@ -0,0 +1,40 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Diagnostics.CodeAnalysis;
+
+namespace System.Security.Cryptography
+{
+    /// <summary>
+    ///   Specifies a key derivation function (KDF) for an HPKE cipher suite.
+    /// </summary>
+    /// <seealso cref="HpkeSuite" />
+    [Experimental(Experimentals.HpkeExperimentalDiagId, UrlFormat = Experimentals.SharedUrlFormat)]
+    public enum HpkeKdf
+    {
+        /// <summary>
+        ///   Indicates that key derivation uses HKDF with SHA-256.
+        /// </summary>
+        HKDF_SHA256 = 1,
+
+        /// <summary>
+        ///   Indicates that key derivation uses HKDF with SHA-384.
+        /// </summary>
+        HKDF_SHA384 = 2,
+
+        /// <summary>
+        ///   Indicates that key derivation uses HKDF with SHA-512.
+        /// </summary>
+        HKDF_SHA512 = 3,
+
+        /// <summary>
+        ///   Indicates that key derivation uses SHAKE128.
+        /// </summary>
+        SHAKE128 = 16,
+
+        /// <summary>
+        ///   Indicates that key derivation uses SHAKE256.
+        /// </summary>
+        SHAKE256 = 17
+    }
+}

src/libraries/Common/src/System/Security/Cryptography/HpkeKdfMetadata.cs

@@ -0,0 +1,61 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+namespace System.Security.Cryptography
+{
+    internal sealed partial class HpkeKdfMetadata
+    {
+        internal HpkeKdf Kdf { get; }
+        internal int Nh { get; }
+        internal bool IsTwoStage { get; }
+        internal string Name { get; }
+        internal int? MaximumInfoLength { get; }
+        internal int? MaximumPskLength { get; }
+        internal int? MaximumPskIdLength { get; }
+
+        // HKDF is limited to 255 hash blocks; HPKE encodes SHAKE output lengths in two bytes.
+        // https://datatracker.ietf.org/doc/html/draft-ietf-hpke-hpke-04#section-4.4
+        internal int MaximumExportLength => IsTwoStage ? 255 * Nh : ushort.MaxValue;
+
+        private HpkeKdfMetadata(HpkeKdf kdf, int nh, bool isTwoStage, string name)
+        {
+            Kdf = kdf;
+            Nh = nh;
+            IsTwoStage = isTwoStage;
+            Name = name;
+
+            if (!IsTwoStage)
+            {
+                // One-stage KDFs length-prefix each of these inputs with a 16-bit length.
+                // HKDF input limits exceed the length representable by a span.
+                // https://datatracker.ietf.org/doc/html/draft-ietf-hpke-hpke-04#section-5.1
+                MaximumInfoLength = ushort.MaxValue;
+                MaximumPskLength = ushort.MaxValue;
+                MaximumPskIdLength = ushort.MaxValue;
+            }
+        }
+
+        internal static HpkeKdfMetadata? Create(HpkeKdf kdf)
+        {
+            switch (kdf)
+            {
+                // HKDF SHAs have limits on their info size, 2^61 - 91 and 2^125 - 155. Since this is well above
+                // A Span's possible length we'll treat it as unlimited.
+                // https://datatracker.ietf.org/doc/html/draft-ietf-hpke-hpke-04#section-7.2
+                case HpkeKdf.HKDF_SHA256:
+                    return new HpkeKdfMetadata(kdf, nh: 32, isTwoStage: true, name: "HKDF-SHA256");
+                case HpkeKdf.HKDF_SHA384:
+                    return new HpkeKdfMetadata(kdf, nh: 48, isTwoStage: true, name: "HKDF-SHA384");
+                case HpkeKdf.HKDF_SHA512:
+                    return new HpkeKdfMetadata(kdf, nh: 64, isTwoStage: true, name: "HKDF-SHA512");
+                case HpkeKdf.SHAKE128:
+                    return new HpkeKdfMetadata(kdf, nh: 32, isTwoStage: false, name: "SHAKE128");
+                case HpkeKdf.SHAKE256:
+                    return new HpkeKdfMetadata(kdf, nh: 64, isTwoStage: false, name: "SHAKE256");
+
+                default:
+                    return null;
+            }
+        }
+    }
+}

src/libraries/Common/src/System/Security/Cryptography/HpkeKem.cs

@@ -0,0 +1,60 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Diagnostics.CodeAnalysis;
+
+namespace System.Security.Cryptography
+{
+    /// <summary>
+    ///   Specifies a key encapsulation mechanism (KEM) for an HPKE cipher suite.
+    /// </summary>
+    /// <seealso cref="HpkeSuite" />
+    [Experimental(Experimentals.HpkeExperimentalDiagId, UrlFormat = Experimentals.SharedUrlFormat)]
+    public enum HpkeKem
+    {
+        /// <summary>
+        ///   Indicates that key encapsulation uses DHKEM with the NIST P-256 curve and HKDF-SHA-256.
+        /// </summary>
+        DHKEM_P256_HKDF_SHA256 = 16,
+
+        /// <summary>
+        ///   Indicates that key encapsulation uses DHKEM with the NIST P-384 curve and HKDF-SHA-384.
+        /// </summary>
+        DHKEM_P384_HKDF_SHA384 = 17,
+
+        /// <summary>
+        ///   Indicates that key encapsulation uses DHKEM with the NIST P-521 curve and HKDF-SHA-512.
+        /// </summary>
+        DHKEM_P521_HKDF_SHA512 = 18,
+
+        /// <summary>
+        ///   Indicates that key encapsulation uses DHKEM with X25519 and HKDF-SHA-256.
+        /// </summary>
+        DHKEM_X25519_HKDF_SHA256 = 32,
+
+        /// <summary>
+        ///   Indicates that key encapsulation uses ML-KEM-512.
+        /// </summary>
+        MLKEM_512 = 64,
+
+        /// <summary>
+        ///   Indicates that key encapsulation uses ML-KEM-768.
+        /// </summary>
+        MLKEM_768 = 65,
+
+        /// <summary>
+        ///   Indicates that key encapsulation uses ML-KEM-1024.
+        /// </summary>
+        MLKEM_1024 = 66,
+
+        /// <summary>
+        ///   Indicates that key encapsulation combines ML-KEM-768 with ECDH using the NIST P-256 curve.
+        /// </summary>
+        MLKEM768_P256 = 80,
+
+        /// <summary>
+        ///   Indicates that key encapsulation combines ML-KEM-1024 with ECDH using the NIST P-384 curve.
+        /// </summary>
+        MLKEM1024_P384 = 81,
+    }
+}

src/libraries/Common/src/System/Security/Cryptography/HpkeKemMetadata.cs

@@ -0,0 +1,63 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+namespace System.Security.Cryptography
+{
+    internal sealed partial class HpkeKemMetadata
+    {
+        internal HpkeKem Kem { get; }
+        internal int Nsk { get; }
+        internal int Npk { get; }
+        internal int Nenc { get; }
+        internal int Nsecret { get; }
+        internal string Name { get; }
+
+        private HpkeKemMetadata(HpkeKem kem, int nsecret, int nenc, int npk, int nsk, string name)
+        {
+            Kem = kem;
+            Nsk = nsk;
+            Npk = npk;
+            Nenc = nenc;
+            Nsecret = nsecret;
+            Name = name;
+            Setup();
+        }
+
+        partial void Setup();
+
+        internal static HpkeKemMetadata? Create(HpkeKem kem)
+        {
+            switch (kem)
+            {
+                // https://datatracker.ietf.org/doc/html/draft-ietf-hpke-hpke-04#section-7.1
+                case HpkeKem.DHKEM_P256_HKDF_SHA256:
+                    return new HpkeKemMetadata(kem, nsecret: 32, nenc: 65, npk: 65, nsk: 32, name: "DHKEM(P-256, HKDF-SHA256)");
+                case HpkeKem.DHKEM_P384_HKDF_SHA384:
+                    return new HpkeKemMetadata(kem, nsecret: 48, nenc: 97, npk: 97, nsk: 48, name: "DHKEM(P-384, HKDF-SHA384)");
+                case HpkeKem.DHKEM_P521_HKDF_SHA512:
+                    return new HpkeKemMetadata(kem, nsecret: 64, nenc: 133, npk: 133, nsk: 66, name: "DHKEM(P-521, HKDF-SHA512)");
+                case HpkeKem.DHKEM_X25519_HKDF_SHA256:
+                    return new HpkeKemMetadata(kem, nsecret: 32, nenc: 32, npk: 32, nsk: 32, name: "DHKEM(X25519, HKDF-SHA256)");
+
+                // https://datatracker.ietf.org/doc/html/draft-ietf-hpke-pq-05#section-8.1
+                // Nsk is the 64-byte seed, not the expanded ML-KEM decapsulation key.
+                case HpkeKem.MLKEM_512:
+                    return new HpkeKemMetadata(kem, nsecret: 32, nenc: 768, npk: 800, nsk: 64, name: "ML-KEM-512");
+                case HpkeKem.MLKEM_768:
+                    return new HpkeKemMetadata(kem, nsecret: 32, nenc: 1088, npk: 1184, nsk: 64, name: "ML-KEM-768");
+                case HpkeKem.MLKEM_1024:
+                    return new HpkeKemMetadata(kem, nsecret: 32, nenc: 1568, npk: 1568, nsk: 64, name: "ML-KEM-1024");
+
+                // https://datatracker.ietf.org/doc/html/draft-ietf-hpke-pq-05#section-8.2
+                // Nsk is the 32-byte seed used to derive both component key pairs.
+                case HpkeKem.MLKEM768_P256:
+                    return new HpkeKemMetadata(kem, nsecret: 32, nenc: 1153, npk: 1249, nsk: 32, name: "MLKEM768-P256");
+                case HpkeKem.MLKEM1024_P384:
+                    return new HpkeKemMetadata(kem, nsecret: 32, nenc: 1665, npk: 1665, nsk: 32, name: "MLKEM1024-P384");
+
+                default:
+                    return null;
+            }
+        }
+    }
+}