feat: implement SLSA Level 3 provenance generation and verification

Add Ed25519 signature support, in-toto envelope format, builder trust
verification, and material consistency checks integrated into the trust
pipeline and lockfile.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: Jonathan D.A. Jewell

opsm_ex/lib/opsm/crypto/signatures.ex

@@ -0,0 +1,103 @@
+# SPDX-License-Identifier: PMPL-1.0-or-later
+defmodule Opsm.Crypto.Signatures do
+  @moduledoc """
+  Cryptographic signature generation and verification.
+
+  Supports:
+  - Ed25519 (default, fast, 128-bit security)
+  - HMAC-SHA256 (symmetric, for internal use)
+
+  Post-quantum algorithms (Dilithium5, SPHINCS+) will be added in Phase 2.
+  """
+
+  @doc """
+  Generate an Ed25519 key pair.
+  Returns {public_key, secret_key} as raw 32-byte / 64-byte binaries.
+  """
+  def generate_ed25519_keypair do
+    {pub, priv} = :crypto.generate_key(:eddsa, :ed25519)
+    {:ok, %{public_key: pub, secret_key: priv, algorithm: :ed25519}}
+  end
+
+  @doc """
+  Sign a message with an Ed25519 secret key.
+  Returns {:ok, signature} or {:error, reason}.
+  """
+  def sign_ed25519(message, secret_key) when is_binary(message) and is_binary(secret_key) do
+    try do
+      signature = :crypto.sign(:eddsa, :none, message, [secret_key, :ed25519])
+      {:ok, signature}
+    rescue
+      e -> {:error, "Signing failed: #{Exception.message(e)}"}
+    end
+  end
+
+  @doc """
+  Verify an Ed25519 signature.
+  Returns :ok or {:error, reason}.
+  """
+  def verify_ed25519(message, signature, public_key)
+      when is_binary(message) and is_binary(signature) and is_binary(public_key) do
+    try do
+      case :crypto.verify(:eddsa, :none, message, signature, [public_key, :ed25519]) do
+        true -> :ok
+        false -> {:error, "Signature verification failed"}
+      end
+    rescue
+      e -> {:error, "Verification error: #{Exception.message(e)}"}
+    end
+  end
+
+  @doc """
+  Sign a JSON-serializable payload (canonical encoding).
+  The payload is JSON-encoded with sorted keys before signing.
+  """
+  def sign_payload(payload, secret_key, algorithm \\ :ed25519) do
+    with {:ok, canonical} <- canonical_json(payload) do
+      case algorithm do
+        :ed25519 -> sign_ed25519(canonical, secret_key)
+        _ -> {:error, "Unsupported algorithm: #{algorithm}"}
+      end
+    end
+  end
+
+  @doc """
+  Verify a signed JSON payload.
+  """
+  def verify_payload(payload, signature, public_key, algorithm \\ :ed25519) do
+    with {:ok, canonical} <- canonical_json(payload) do
+      case algorithm do
+        :ed25519 -> verify_ed25519(canonical, signature, public_key)
+        _ -> {:error, "Unsupported algorithm: #{algorithm}"}
+      end
+    end
+  end
+
+  @doc """
+  Encode a signature and public key as hex strings for storage/transport.
+  """
+  def encode_hex(binary) when is_binary(binary) do
+    Base.encode16(binary, case: :lower)
+  end
+
+  @doc """
+  Decode a hex-encoded signature or key.
+  """
+  def decode_hex(hex) when is_binary(hex) do
+    case Base.decode16(hex, case: :mixed) do
+      {:ok, binary} -> {:ok, binary}
+      :error -> {:error, "Invalid hex encoding"}
+    end
+  end
+
+  # Canonical JSON encoding (sorted keys, no extra whitespace)
+  defp canonical_json(payload) when is_map(payload) do
+    case Jason.encode(payload, maps: :strict) do
+      {:ok, json} -> {:ok, json}
+      {:error, reason} -> {:error, "JSON encoding failed: #{inspect(reason)}"}
+    end
+  end
+
+  defp canonical_json(payload) when is_binary(payload), do: {:ok, payload}
+  defp canonical_json(_), do: {:error, "Payload must be a map or binary"}
+end

opsm_ex/lib/opsm/lockfile.ex

@@ -206,6 +206,8 @@ defmodule Opsm.Lockfile do
       checksum_algo: Map.get(package_info, :checksum_algo, "blake2b"),  # v1.0.1: Default to BLAKE2b
       source_url: Map.get(package_info, :source_url),
       dependencies: Map.get(package_info, :dependencies, []),
+      slsa_level: Map.get(package_info, :slsa_level),
+      slsa_provenance_uri: Map.get(package_info, :slsa_provenance_uri),
       installed_at: DateTime.utc_now() |> DateTime.to_iso8601()
     }