libcamera: Add PubKey class

Add a new PubKey class to handle public key signature verification. The
implementation is based on the gnutls library, which is added as an
optional dependency. If gnutls is not found, signature verification will
unconditionally fail.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>

4 files changed, 143 insertions, 0 deletions

diff --git a/src/libcamera/include/meson.build b/src/libcamera/include/meson.build
index 921ed5a0..5aaa9947 100644
--- a/src/libcamera/include/meson.build
+++ b/src/libcamera/include/meson.build
@@ -21,6 +21,7 @@ libcamera_headers = files([
     'message.h',
     'pipeline_handler.h',
     'process.h',
+    'pub_key.h',
     'semaphore.h',
     'thread.h',
     'utils.h',
diff --git a/src/libcamera/include/pub_key.h b/src/libcamera/include/pub_key.h
new file mode 100644
index 00000000..f35bf373
--- /dev/null
+++ b/src/libcamera/include/pub_key.h
@@ -0,0 +1,38 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2020, Google Inc.
+ *
+ * pub_key.h - Public key signature verification
+ */
+#ifndef __LIBCAMERA_PUB_KEY_H__
+#define __LIBCAMERA_PUB_KEY_H__
+
+#include <stdint.h>
+
+#include <libcamera/span.h>
+
+#if HAVE_GNUTLS
+struct gnutls_pubkey_st;
+#endif
+
+namespace libcamera {
+
+class PubKey
+{
+public:
+	PubKey(Span<const uint8_t> key);
+	~PubKey();
+
+	bool isValid() const { return valid_; }
+	bool verify(Span<const uint8_t> data, Span<const uint8_t> sig) const;
+
+private:
+	bool valid_;
+#if HAVE_GNUTLS
+	struct gnutls_pubkey_st *pubkey_;
+#endif
+};
+
+} /* namespace libcamera */
+
+#endif /* __LIBCAMERA_PUB_KEY_H__ */
diff --git a/src/libcamera/meson.build b/src/libcamera/meson.build
index 4f5c4167..c2a657e4 100644
--- a/src/libcamera/meson.build
+++ b/src/libcamera/meson.build
@@ -34,6 +34,7 @@ libcamera_sources = files([
     'pipeline_handler.cpp',
     'pixelformats.cpp',
     'process.cpp',
+    'pub_key.cpp',
     'request.cpp',
     'semaphore.cpp',
     'signal.cpp',
@@ -61,8 +62,13 @@ subdir('proxy')
 
 libatomic = cc.find_library('atomic', required : false)
 libdl = cc.find_library('dl')
+libgnutls = cc.find_library('gnutls', required : false)
 libudev = dependency('libudev', required : false)
 
+if libgnutls.found()
+    config_h.set('HAVE_GNUTLS', 1)
+endif
+
 if libudev.found()
     config_h.set('HAVE_LIBUDEV', 1)
     libcamera_sources += files([
@@ -98,6 +104,7 @@ libcamera_sources += version_cpp
 libcamera_deps = [
     libatomic,
     libdl,
+    libgnutls,
     libudev,
     dependency('threads'),
 ]
diff --git a/src/libcamera/pub_key.cpp b/src/libcamera/pub_key.cpp
new file mode 100644
index 00000000..064d2dd2
--- /dev/null
+++ b/src/libcamera/pub_key.cpp
@@ -0,0 +1,97 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2020, Google Inc.
+ *
+ * pub_key.cpp - Public key signature verification
+ */
+
+#include "pub_key.h"
+
+#if HAVE_GNUTLS
+#include <gnutls/abstract.h>
+#endif
+
+/**
+ * \file pub_key.h
+ * \brief Public key signature verification
+ */
+
+namespace libcamera {
+
+/**
+ * \class PubKey
+ * \brief Public key wrapper for signature verification
+ *
+ * The PubKey class wraps a public key and implements signature verification. It
+ * only supports RSA keys and the RSA-SHA256 signature algorithm.
+ */
+
+/**
+ * \brief Construct a PubKey from key data
+ * \param[in] key Key data encoded in DER format
+ */
+PubKey::PubKey(Span<const uint8_t> key)
+	: valid_(false)
+{
+#if HAVE_GNUTLS
+	int ret = gnutls_pubkey_init(&pubkey_);
+	if (ret < 0)
+		return;
+
+	const gnutls_datum_t gnuTlsKey{
+		const_cast<unsigned char *>(key.data()),
+		static_cast<unsigned int>(key.size())
+	};
+	ret = gnutls_pubkey_import(pubkey_, &gnuTlsKey, GNUTLS_X509_FMT_DER);
+	if (ret < 0)
+		return;
+
+	valid_ = true;
+#endif
+}
+
+PubKey::~PubKey()
+{
+#if HAVE_GNUTLS
+	gnutls_pubkey_deinit(pubkey_);
+#endif
+}
+
+/**
+ * \fn bool PubKey::isValid() const
+ * \brief Check is the public key is valid
+ * \return True if the public key is valid, false otherwise
+ */
+
+/**
+ * \brief Verify signature on data
+ * \param[in] data The signed data
+ * \param[in] sig The signature
+ *
+ * Verify that the signature \a sig matches the signed \a data for the public
+ * key. The signture algorithm is hardcoded to RSA-SHA256.
+ *
+ * \return True if the signature is valid, false otherwise
+ */
+bool PubKey::verify(Span<const uint8_t> data, Span<const uint8_t> sig) const
+{
+#if HAVE_GNUTLS
+	const gnutls_datum_t gnuTlsData{
+		const_cast<unsigned char *>(data.data()),
+		static_cast<unsigned int>(data.size())
+	};
+
+	const gnutls_datum_t gnuTlsSig{
+		const_cast<unsigned char *>(sig.data()),
+		static_cast<unsigned int>(sig.size())
+	};
+
+	int ret = gnutls_pubkey_verify_data2(pubkey_, GNUTLS_SIGN_RSA_SHA256, 0,
+					     &gnuTlsData, &gnuTlsSig);
+	return ret >= 0;
+#else
+	return false;
+#endif
+}
+
+} /* namespace libcamera */