netutils/dropbear: back SHA-256 and HMAC-SHA256 with NuttX crypto

Swap the libtomcrypt sha256/hmac state for the kernel SHA2/HMAC-SHA256 contexts and provide adapters.

Fix format

Signed-off-by: Felipe Moura <moura.fmo@gmail.com>

netutils/dropbear/CMakeLists.txt

@@ -63,6 +63,11 @@ if(CONFIG_NETUTILS_DROPBEAR)
           patch -s -N -l -p1 -d "${DROPBEAR_UNPACKNAME}" -i
           "${CMAKE_CURRENT_SOURCE_DIR}/patch/0004-use-nuttx-unused-macro.patch"
         WORKING_DIRECTORY "${CMAKE_CURRENT_SOURCE_DIR}")
+      execute_process(
+        COMMAND
+          patch -s -N -l -p1 -d "${DROPBEAR_UNPACKNAME}" -i
+          "${CMAKE_CURRENT_SOURCE_DIR}/patch/0005-use-nuttx-sha256-hmac.patch"
+        WORKING_DIRECTORY "${CMAKE_CURRENT_SOURCE_DIR}")
       message(STATUS "Generating default_options_guard.h")
       execute_process(
         COMMAND
@@ -135,6 +140,17 @@ if(CONFIG_NETUTILS_DROPBEAR)
   file(GLOB_RECURSE LIBTOMCRYPT_SRCS CONFIGURE_DEPENDS
        "${CMAKE_CURRENT_SOURCE_DIR}/dropbear/libtomcrypt/src/*.c")
   list(FILTER LIBTOMCRYPT_SRCS EXCLUDE REGEX ".*/prngs/sober128tab\\.c$")
+
+  if(CONFIG_NETUTILS_DROPBEAR_NUTTX_CRYPTO)
+    # Drop the bundled libtomcrypt modules replaced by the NuttX adapters.
+    list(FILTER LIBTOMCRYPT_SRCS EXCLUDE REGEX ".*/hashes/sha2/sha256\\.c$")
+    list(FILTER LIBTOMCRYPT_SRCS EXCLUDE REGEX ".*/mac/hmac/hmac_init\\.c$")
+    list(FILTER LIBTOMCRYPT_SRCS EXCLUDE REGEX ".*/mac/hmac/hmac_process\\.c$")
+    list(FILTER LIBTOMCRYPT_SRCS EXCLUDE REGEX ".*/mac/hmac/hmac_done\\.c$")
+    list(APPEND DROPBEAR_SRCS port/dropbear_ltc_sha256.c
+         port/dropbear_ltc_hmac_sha256.c)
+  endif()
+
   list(APPEND DROPBEAR_SRCS ${LIBTOMCRYPT_SRCS})
 
   if(CONFIG_NETUTILS_DROPBEAR_SCP)
@@ -195,6 +211,11 @@ if(CONFIG_NETUTILS_DROPBEAR)
     ${PROGNAME} PRIVATE LOCALOPTIONS_H_EXISTS=1 DROPBEAR_NUTTX=1
                         DROPBEAR_NUTTX_PASSWD=1)
 
+  if(CONFIG_NETUTILS_DROPBEAR_NUTTX_CRYPTO)
+    target_compile_definitions(${PROGNAME} PRIVATE DROPBEAR_NUTTX_SHA256=1
+                                                   DROPBEAR_NUTTX_HMAC_SHA256=1)
+  endif()
+
   if(CONFIG_NETUTILS_DROPBEAR_SCP)
     target_compile_definitions(
       scp PRIVATE LOCALOPTIONS_H_EXISTS=1 DROPBEAR_NUTTX=1

netutils/dropbear/Kconfig

@@ -90,6 +90,16 @@ config NETUTILS_DROPBEAR_SCP_PRIORITY
 	default 100
 	depends on NETUTILS_DROPBEAR_SCP
 
+config NETUTILS_DROPBEAR_NUTTX_CRYPTO
+	bool "Use NuttX kernel crypto primitives"
+	default y
+	depends on BUILD_FLAT
+	---help---
+		Back Dropbear's SHA-256 and HMAC-SHA256 primitives with the NuttX
+		kernel crypto implementation instead of the bundled libtomcrypt
+		modules, reducing flash usage.  This requires a flat build because
+		Dropbear calls the kernel crypto functions directly.
+
 config NETUTILS_DROPBEAR_PORT
 	int "Dropbear listen port"
 	default 2222

netutils/dropbear/Makefile

@@ -63,6 +63,11 @@ CFLAGS += ${DEFINE_PREFIX}DROPBEAR_NUTTX=1
 CFLAGS += ${DEFINE_PREFIX}DROPBEAR_NUTTX_PASSWD=1
 CFLAGS += -Wno-pointer-sign -Wno-format
 
+ifneq ($(CONFIG_NETUTILS_DROPBEAR_NUTTX_CRYPTO),)
+CFLAGS += ${DEFINE_PREFIX}DROPBEAR_NUTTX_SHA256=1
+CFLAGS += ${DEFINE_PREFIX}DROPBEAR_NUTTX_HMAC_SHA256=1
+endif
+
 dropbear_nshsession.c_CFLAGS += ${DEFINE_PREFIX}Channel=dropbear_channel
 dropbear_nshsession.c_CFLAGS += ${DEFINE_PREFIX}ChanType=dropbear_chantype
 
@@ -119,6 +124,20 @@ CSRCS += \
 TOMMATH_SRCS = $(shell if [ -d "$(DROPBEAR_UNPACKNAME)/libtommath" ]; then find "$(DROPBEAR_UNPACKNAME)/libtommath" -name "*.c"; fi)
 TOMCRYPT_SRCS = $(shell if [ -d "$(DROPBEAR_UNPACKNAME)/libtomcrypt/src" ]; then find "$(DROPBEAR_UNPACKNAME)/libtomcrypt/src" -name "*.c" ! -name "sober128tab.c"; fi)
 
+ifneq ($(CONFIG_NETUTILS_DROPBEAR_NUTTX_CRYPTO),)
+# Drop the bundled libtomcrypt modules replaced by the NuttX adapters.
+
+TOMCRYPT_SRCS := $(filter-out \
+	%/hashes/sha2/sha256.c \
+	%/mac/hmac/hmac_init.c \
+	%/mac/hmac/hmac_process.c \
+	%/mac/hmac/hmac_done.c, \
+	$(TOMCRYPT_SRCS))
+
+CSRCS += port/dropbear_ltc_sha256.c
+CSRCS += port/dropbear_ltc_hmac_sha256.c
+endif
+
 CSRCS += $(TOMMATH_SRCS)
 CSRCS += $(TOMCRYPT_SRCS)
 
@@ -161,6 +180,7 @@ $(DROPBEAR_UNPACKNAME): $(DROPBEAR_ZIP)
 	$(Q) $(PATCH) -s -N -l -p1 -d $(DROPBEAR_UNPACKNAME) -i $(APPDIR)$(DELIM)netutils$(DELIM)dropbear$(DELIM)patch$(DELIM)0002-use-nuttx-passwd-auth.patch; true
 	$(Q) $(PATCH) -s -N -l -p1 -d $(DROPBEAR_UNPACKNAME) -i $(APPDIR)$(DELIM)netutils$(DELIM)dropbear$(DELIM)patch$(DELIM)0003-allow-localoptions-to-override-tracking-malloc.patch; true
 	$(Q) $(PATCH) -s -N -l -p1 -d $(DROPBEAR_UNPACKNAME) -i $(APPDIR)$(DELIM)netutils$(DELIM)dropbear$(DELIM)patch$(DELIM)0004-use-nuttx-unused-macro.patch; true
+	$(Q) $(PATCH) -s -N -l -p1 -d $(DROPBEAR_UNPACKNAME) -i $(APPDIR)$(DELIM)netutils$(DELIM)dropbear$(DELIM)patch$(DELIM)0005-use-nuttx-sha256-hmac.patch; true
 	@echo "Generating default_options_guard.h"
 	$(Q) sh $(DROPBEAR_UNPACKNAME)$(DELIM)src$(DELIM)ifndef_wrapper.sh \
 		< $(DROPBEAR_UNPACKNAME)$(DELIM)src$(DELIM)default_options.h \

netutils/dropbear/patch/0005-use-nuttx-sha256-hmac.patch

@@ -0,0 +1,45 @@
+--- a/libtomcrypt/src/headers/tomcrypt_hash.h
++++ b/libtomcrypt/src/headers/tomcrypt_hash.h
+@@ -30,11 +30,18 @@ struct sha512_state {
+ #endif
+ 
+ #ifdef LTC_SHA256
++#ifdef DROPBEAR_NUTTX_SHA256
++#include <crypto/sha2.h>
++struct sha256_state {
++    SHA2_CTX ctx;
++};
++#else
+ struct sha256_state {
+     ulong64 length;
+     ulong32 state[8], curlen;
+     unsigned char buf[64];
+ };
++#endif
+ #endif
+ 
+ #ifdef LTC_SHA1
+--- a/libtomcrypt/src/headers/tomcrypt_mac.h
++++ b/libtomcrypt/src/headers/tomcrypt_mac.h
+@@ -7,6 +7,13 @@
+  */
+ 
+ #ifdef LTC_HMAC
++#ifdef DROPBEAR_NUTTX_HMAC_SHA256
++#include <crypto/hmac.h>
++typedef struct Hmac_state {
++     HMAC_SHA256_CTX ctx;
++     int             hash;
++} hmac_state;
++#else
+ typedef struct Hmac_state {
+      hash_state     md;
+      int            hash;
+@@ -14,6 +21,7 @@ typedef struct Hmac_state {
+      unsigned char  *key;
+ } hmac_state;
+ 
++#endif
+ int hmac_init(hmac_state *hmac, int hash, const unsigned char *key, unsigned long keylen);
+ int hmac_process(hmac_state *hmac, const unsigned char *in, unsigned long inlen);
+ int hmac_done(hmac_state *hmac, unsigned char *out, unsigned long *outlen);

netutils/dropbear/port/dropbear_ltc_hmac_sha256.c

@@ -0,0 +1,103 @@
+/****************************************************************************
+ * apps/netutils/dropbear/port/dropbear_ltc_hmac_sha256.c
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ ****************************************************************************/
+
+/* LibTomCrypt-compatible HMAC API backed by NuttX crypto/hmac.  The NuttX
+ * Dropbear configuration only enables hmac-sha2-256.
+ */
+
+/****************************************************************************
+ * Included Files
+ ****************************************************************************/
+
+#include "includes.h"
+
+#include <crypto/hmac.h>
+
+/****************************************************************************
+ * Private Functions
+ ****************************************************************************/
+
+static int dropbear_hmac_hash_is_sha256(int hash)
+{
+  int ret;
+
+  ret = hash_is_valid(hash);
+  if (ret != CRYPT_OK)
+    {
+      return ret;
+    }
+
+  if (hash_descriptor[hash].hashsize != SHA256_DIGEST_LENGTH ||
+      hash_descriptor[hash].blocksize != SHA256_BLOCK_LENGTH)
+    {
+      return CRYPT_INVALID_HASH;
+    }
+
+  return CRYPT_OK;
+}
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+int hmac_init(hmac_state *hmac, int hash, const unsigned char *key,
+              unsigned long keylen)
+{
+  int ret;
+
+  LTC_ARGCHK(hmac != NULL);
+  LTC_ARGCHK(key != NULL);
+
+  if (keylen == 0)
+    {
+      return CRYPT_INVALID_KEYSIZE;
+    }
+
+  ret = dropbear_hmac_hash_is_sha256(hash);
+  if (ret != CRYPT_OK)
+    {
+      return ret;
+    }
+
+  hmac->hash = hash;
+  hmac_sha256_init(&hmac->ctx, key, (u_int)keylen);
+  return CRYPT_OK;
+}
+
+int hmac_process(hmac_state *hmac, const unsigned char *in,
+                 unsigned long inlen)
+{
+  LTC_ARGCHK(hmac != NULL);
+  LTC_ARGCHK(in != NULL || inlen == 0);
+
+  hmac_sha256_update(&hmac->ctx, in, (u_int)inlen);
+  return CRYPT_OK;
+}
+
+int hmac_done(hmac_state *hmac, unsigned char *out, unsigned long *outlen)
+{
+  uint8_t digest[SHA256_DIGEST_LENGTH];
+  unsigned long copylen;
+
+  LTC_ARGCHK(hmac != NULL);
+  LTC_ARGCHK(out != NULL);
+  LTC_ARGCHK(outlen != NULL);
+
+  if (dropbear_hmac_hash_is_sha256(hmac->hash) != CRYPT_OK)
+    {
+      return CRYPT_INVALID_HASH;
+    }
+
+  hmac_sha256_final(digest, &hmac->ctx);
+
+  copylen = MIN(*outlen, SHA256_DIGEST_LENGTH);
+  memcpy(out, digest, copylen);
+  *outlen = copylen;
+
+  zeromem(digest, sizeof(digest));
+  zeromem(hmac, sizeof(*hmac));
+  return CRYPT_OK;
+}

netutils/dropbear/port/dropbear_ltc_sha256.c

@@ -0,0 +1,75 @@
+/****************************************************************************
+ * apps/netutils/dropbear/port/dropbear_ltc_sha256.c
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ ****************************************************************************/
+
+/* LibTomCrypt-compatible SHA256 descriptor backed by NuttX crypto/sha2.
+ * Dropbear still expects the libtomcrypt hash API for KEX and HMAC.  This
+ * adapter keeps that API while avoiding the bundled SHA256 implementation.
+ */
+
+/****************************************************************************
+ * Included Files
+ ****************************************************************************/
+
+#include "includes.h"
+
+#include <crypto/sha2.h>
+
+/****************************************************************************
+ * Public Data
+ ****************************************************************************/
+
+const struct ltc_hash_descriptor sha256_desc =
+{
+  "sha256",
+  0,
+  SHA256_DIGEST_LENGTH,
+  SHA256_BLOCK_LENGTH,
+  { 2, 16, 840, 1, 101, 3, 4, 2, 1 },
+  9,
+
+  sha256_init,
+  sha256_process,
+  sha256_done,
+  sha256_test,
+  NULL
+};
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+int sha256_init(hash_state *md)
+{
+  LTC_ARGCHK(md != NULL);
+
+  sha256init(&md->sha256.ctx);
+  return CRYPT_OK;
+}
+
+int sha256_process(hash_state *md, const unsigned char *in,
+                   unsigned long inlen)
+{
+  LTC_ARGCHK(md != NULL);
+  LTC_ARGCHK(in != NULL || inlen == 0);
+
+  sha256update(&md->sha256.ctx, in, inlen);
+  return CRYPT_OK;
+}
+
+int sha256_done(hash_state *md, unsigned char *out)
+{
+  LTC_ARGCHK(md != NULL);
+  LTC_ARGCHK(out != NULL);
+
+  sha256final(out, &md->sha256.ctx);
+  zeromem(md, sizeof(*md));
+  return CRYPT_OK;
+}
+
+int sha256_test(void)
+{
+  return CRYPT_NOP;
+}