LibCrypto: Implement ECPrivateKey and ECPublicKey

Added basic EC private and public key definitions as well as ASN.1
encoding and decoding.

A lot of refactoring can be made around the ASN.1 processing (here and
in other parts of the codebase) by utilizing what is available
in `LibCrypto::Certificate` as macros, but I think it's outside the
scope of implementing ECDH support for WebCryptoAPI.

Libraries/LibCrypto/PK/EC.h

@@ -0,0 +1,87 @@
+/*
+ * Copyright (c) 2024, Altomani Gianluca <altomanigianluca@gmail.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/ByteBuffer.h>
+#include <AK/StringView.h>
+#include <LibCrypto/ASN1/DER.h>
+#include <LibCrypto/PK/PK.h>
+
+namespace Crypto::PK {
+
+template<typename Integer = UnsignedBigInteger>
+class ECPublicKey {
+public:
+    ECPublicKey(Integer x, Integer y)
+        : m_x(move(x))
+        , m_y(move(y))
+    {
+    }
+
+    ECPublicKey()
+        : m_x(0)
+        , m_y(0)
+    {
+    }
+
+    Integer const& x() const { return m_x; }
+    Integer const& y() const { return m_y; }
+
+    ErrorOr<ByteBuffer> to_uncompressed() const
+    {
+        auto bytes = TRY(ByteBuffer::create_uninitialized(1 + m_x.byte_length() + m_y.byte_length()));
+        bytes[0] = 0x04; // uncompressed
+        auto x_size = m_x.export_data(bytes.span().slice(1));
+        auto y_size = m_y.export_data(bytes.span().slice(1 + x_size));
+        return bytes.slice(0, 1 + x_size + y_size);
+    }
+
+private:
+    Integer m_x;
+    Integer m_y;
+};
+
+// https://www.rfc-editor.org/rfc/rfc5915#section-3
+template<typename Integer = UnsignedBigInteger>
+class ECPrivateKey {
+public:
+    ECPrivateKey(Integer d, Optional<Vector<int>> parameters, Optional<ECPublicKey<Integer>> public_key)
+        : m_d(move(d))
+        , m_parameters(parameters)
+        , m_public_key(public_key)
+    {
+    }
+
+    ECPrivateKey() = default;
+
+    Integer const& d() const { return m_d; }
+    Optional<Vector<int> const&> parameters() const { return m_parameters; }
+    Optional<ECPublicKey<Integer> const&> public_key() const { return m_public_key; }
+
+    ErrorOr<ByteBuffer> export_as_der() const;
+
+private:
+    Integer m_d;
+    Optional<Vector<int>> m_parameters;
+    Optional<ECPublicKey<Integer>> m_public_key;
+};
+
+template<typename PubKey, typename PrivKey>
+struct ECKeyPair {
+    PubKey public_key;
+    PrivKey private_key;
+};
+
+using IntegerType = UnsignedBigInteger;
+class EC : public PKSystem<ECPrivateKey<IntegerType>, ECPublicKey<IntegerType>> {
+public:
+    using KeyPairType = ECKeyPair<PublicKeyType, PrivateKeyType>;
+
+    static ErrorOr<KeyPairType> parse_ec_key(ReadonlyBytes der);
+};
+
+}