[libcamera-devel] [PATCH 5/5] libcamera: pub_key: Support openssl as an alternative to gnutls

[Laurent Pinchart]

Support verify IPA signatures with openssl as an alternative to gnutls,
to offer more flexibility in the selection of dependencies. Use gnutls
by default, for no specific reason as both are equally well supported.

Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
---
 README.rst                           |  2 +-
 include/libcamera/internal/pub_key.h |  8 +++++--
 src/libcamera/meson.build            | 16 +++++++++----
 src/libcamera/pub_key.cpp            | 35 ++++++++++++++++++++++++----
 4 files changed, 50 insertions(+), 11 deletions(-)

diff --git a/README.rst b/README.rst
index 3606057ff706..e9dd4207ae55 100644
--- a/README.rst
+++ b/README.rst
@@ -61,7 +61,7 @@ for the libcamera core: [required]
         libyaml-dev python3-yaml python3-ply python3-jinja2
 
 for IPA module signing: [recommended]
-        libgnutls28-dev openssl
+        Either libgnutls28-dev or libssl-dev, openssl
 
         Without IPA module signing, all IPA modules will be isolated in a
         separate process. This adds an unnecessary extra overhead at runtime.
diff --git a/include/libcamera/internal/pub_key.h b/include/libcamera/internal/pub_key.h
index a22ba037cff6..ea7d9af84515 100644
--- a/include/libcamera/internal/pub_key.h
+++ b/include/libcamera/internal/pub_key.h
@@ -11,7 +11,9 @@
 
 #include <libcamera/base/span.h>
 
-#if HAVE_GNUTLS
+#if HAVE_CRYPTO
+struct rsa_st;
+#elif HAVE_GNUTLS
 struct gnutls_pubkey_st;
 #endif
 
@@ -28,7 +30,9 @@ public:
 
 private:
 	bool valid_;
-#if HAVE_GNUTLS
+#if HAVE_CRYPTO
+	struct rsa_st *pubkey_;
+#elif HAVE_GNUTLS
 	struct gnutls_pubkey_st *pubkey_;
 #endif
 };
diff --git a/src/libcamera/meson.build b/src/libcamera/meson.build
index e144d4f9ae70..ce1f0f2f3ef6 100644
--- a/src/libcamera/meson.build
+++ b/src/libcamera/meson.build
@@ -65,14 +65,22 @@ subdir('pipeline')
 subdir('proxy')
 
 libdl = cc.find_library('dl')
-libgnutls = dependency('gnutls', required : false)
 libudev = dependency('libudev', required : false)
 libyaml = dependency('yaml-0.1', required : false)
 
-if libgnutls.found()
+# Use one of gnutls or libcrypto (provided by OpenSSL), trying gnutls first.
+libcrypto = dependency('gnutls', required : false)
+if libcrypto.found()
     config_h.set('HAVE_GNUTLS', 1)
 else
-    warning('gnutls not found, all IPA modules will be isolated')
+    libcrypto = dependency('libcrypto', required : false)
+    if libcrypto.found()
+        config_h.set('HAVE_CRYPTO', 1)
+    endif
+endif
+
+if not libcrypto.found()
+    warning('Neither gnutls nor libcrypto found, all IPA modules will be isolated')
 endif
 
 if liblttng.found()
@@ -137,8 +145,8 @@ libcamera_deps = [
     libatomic,
     libcamera_base,
     libcamera_base_private,
+    libcrypto,
     libdl,
-    libgnutls,
     liblttng,
     libudev,
     libyaml,
diff --git a/src/libcamera/pub_key.cpp b/src/libcamera/pub_key.cpp
index b2045a103bc0..723f311b91a2 100644
--- a/src/libcamera/pub_key.cpp
+++ b/src/libcamera/pub_key.cpp
@@ -7,7 +7,12 @@
 
 #include "libcamera/internal/pub_key.h"
 
-#if HAVE_GNUTLS
+#if HAVE_CRYPTO
+#include <openssl/bio.h>
+#include <openssl/rsa.h>
+#include <openssl/ssl.h>
+#include <openssl/x509.h>
+#elif HAVE_GNUTLS
 #include <gnutls/abstract.h>
 #endif
 
@@ -33,7 +38,14 @@ namespace libcamera {
 PubKey::PubKey([[maybe_unused]] Span<const uint8_t> key)
 	: valid_(false)
 {
-#if HAVE_GNUTLS
+#if HAVE_CRYPTO
+	const uint8_t *data = key.data();
+	pubkey_ = d2i_RSA_PUBKEY(nullptr, &data, key.size());
+	if (!pubkey_)
+		return;
+
+	valid_ = true;
+#elif HAVE_GNUTLS
 	int ret = gnutls_pubkey_init(&pubkey_);
 	if (ret < 0)
 		return;
@@ -52,7 +64,9 @@ PubKey::PubKey([[maybe_unused]] Span<const uint8_t> key)
 
 PubKey::~PubKey()
 {
-#if HAVE_GNUTLS
+#if HAVE_CRYPTO
+	RSA_free(pubkey_);
+#elif HAVE_GNUTLS
 	gnutls_pubkey_deinit(pubkey_);
 #endif
 }
@@ -79,7 +93,20 @@ bool PubKey::verify([[maybe_unused]] Span<const uint8_t> data,
 	if (!valid_)
 		return false;
 
-#if HAVE_GNUTLS
+#if HAVE_CRYPTO
+	/* Calculate the SHA256 digest of the data. */
+	SHA256_CTX ctx;
+	SHA256_Init(&ctx);
+	SHA256_Update(&ctx, data.data(), data.size());
+
+	uint8_t digest[SHA256_DIGEST_LENGTH];
+	SHA256_Final(digest, &ctx);
+
+	/* Decrypt the signature and verify it matches the digest. */
+	int ret = RSA_verify(NID_sha256, digest, SHA256_DIGEST_LENGTH,
+			     sig.data(), sig.size(), pubkey_);
+	return ret == 1;
+#elif HAVE_GNUTLS
 	const gnutls_datum_t gnuTlsData{
 		const_cast<unsigned char *>(data.data()),
 		static_cast<unsigned int>(data.size())
-- 
Regards,

Laurent Pinchart