Mini sign, a tiny (<500 bytes) implementation of COSE_Sign1

CMakeLists.txt

@@ -67,6 +67,7 @@ set(T_COSE_SRC_COMMON
     src/t_cose_sign1_verify.c
     src/t_cose_util.c
     src/t_cose_short_circuit.c
+    src/t_cose_mini_sign1_sign.c
 )
 
 find_package(QCBOR REQUIRED)
@@ -110,6 +111,7 @@ if (BUILD_TESTS)
 
     if (NOT CRYPTO_PROVIDER STREQUAL "Test")
         list(APPEND TEST_SRC_COMMON test/t_cose_sign_verify_test.c)
+        list(APPEND TEST_SRC_COMMON test/t_cose_mini_sign1_sign_test.c)
     endif()
 
     if (CRYPTO_PROVIDER STREQUAL "MbedTLS")

Makefile.ossl

@@ -54,15 +54,15 @@ C_OPTS=-Os -fPIC
 
 # ---- T_COSE Config and test options ----
 TEST_CONFIG_OPTS=
-TEST_OBJ=test/t_cose_test.o test/run_tests.o test/t_cose_sign_verify_test.o test/t_cose_make_test_messages.o $(CRYPTO_TEST_OBJ)
+TEST_OBJ=test/t_cose_test.o test/run_tests.o test/t_cose_sign_verify_test.o test/t_cose_make_test_messages.o test/t_cose_mini_sign1_sign_test.o $(CRYPTO_TEST_OBJ)
 
 
 # ---- the main body that is invariant ----
 INC=-I inc -I test -I src
 ALL_INC=$(INC) $(CRYPTO_INC) $(QCBOR_INC) 
 CFLAGS=$(CMD_LINE) $(ALL_INC) $(C_OPTS) $(TEST_CONFIG_OPTS) $(CRYPTO_CONFIG_OPTS)
 
-SRC_OBJ=src/t_cose_sign1_verify.o src/t_cose_sign1_sign.o src/t_cose_util.o src/t_cose_parameters.o src/t_cose_short_circuit.o
+SRC_OBJ=src/t_cose_sign1_verify.o src/t_cose_sign1_sign.o src/t_cose_mini_sign1_sign.o src/t_cose_util.o src/t_cose_parameters.o src/t_cose_short_circuit.o
 
 .PHONY: all install install_headers install_so uninstall clean
 

Makefile.psa

@@ -56,15 +56,15 @@ C_OPTS=-Os -fPIC
 
 # ---- T_COSE Config and test options ----
 TEST_CONFIG_OPTS=
-TEST_OBJ=test/t_cose_test.o test/run_tests.o test/t_cose_sign_verify_test.o test/t_cose_make_test_messages.o $(CRYPTO_TEST_OBJ)
+TEST_OBJ=test/t_cose_test.o test/run_tests.o test/t_cose_sign_verify_test.o test/t_cose_make_test_messages.o test/t_cose_mini_sign1_sign_test.o $(CRYPTO_TEST_OBJ)
 
 
 # ---- the main body that is invariant ----
 INC=-I inc -I test -I src
 ALL_INC=$(INC) $(CRYPTO_INC) $(QCBOR_INC)
 CFLAGS=$(CMD_LINE) $(ALL_INC) $(C_OPTS) $(TEST_CONFIG_OPTS) $(CRYPTO_CONFIG_OPTS)
 
-SRC_OBJ=src/t_cose_sign1_verify.o src/t_cose_sign1_sign.o src/t_cose_util.o src/t_cose_parameters.o src/t_cose_short_circuit.o
+SRC_OBJ=src/t_cose_sign1_verify.o src/t_cose_sign1_sign.o src/t_cose_mini_sign1_sign.o src/t_cose_util.o src/t_cose_parameters.o src/t_cose_short_circuit.o
 
 .PHONY: all install install_headers install_so uninstall clean
 

Makefile.test

@@ -46,7 +46,7 @@ INC=-I inc -I test -I src
 ALL_INC=$(INC) $(CRYPTO_INC) $(QCBOR_INC)
 CFLAGS=$(CMD_LINE) $(ALL_INC) $(C_OPTS) $(TEST_CONFIG_OPTS) $(CRYPTO_CONFIG_OPTS)
 
-SRC_OBJ=src/t_cose_sign1_verify.o src/t_cose_sign1_sign.o src/t_cose_util.o src/t_cose_parameters.o src/t_cose_short_circuit.o
+SRC_OBJ=src/t_cose_sign1_verify.o src/t_cose_sign1_sign.o src/t_cose_mini_sign1_sign.o src/t_cose_util.o src/t_cose_parameters.o src/t_cose_short_circuit.o
 
 .PHONY: all clean
 

inc/t_cose/t_cose_common.h

@@ -403,6 +403,10 @@ enum t_cose_err_t {
 
     /** The auxiliary buffer is too small */
     T_COSE_ERR_AUXILIARY_BUFFER_SIZE = 39,
+
+    /** The size or length is larger than can be handled. */
+    T_COSE_ERR_TOO_LONG = 40
+
 };
 
 

inc/t_cose/t_cose_mini_sign1_sign.h

@@ -0,0 +1,111 @@
+/*
+ * t_cose_mini_sign1_sign.h
+ *
+ * Copyright 2022-2023, Laurence Lundblade
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
+ * See BSD-3-Clause license in README.md
+ */
+
+
+#ifndef __T_COSE_MINI_SIGN_H__
+#define __T_COSE_MINI_SIGN_H__
+
+
+#include "t_cose/q_useful_buf.h"
+#include "t_cose/t_cose_common.h"
+
+
+#ifdef __cplusplus
+extern "C" {
+#if 0
+} /* Keep editor indention formatting happy */
+#endif
+#endif
+
+
+
+/* The output buffer must be this much larger than the payload size. */
+#define T_COSE_MINI_SIGN_SIZE_OVERHEAD_ES256 \
+    1 + /* Open the array */ \
+    5 + /* The header parameters */ \
+    3 + /* The CBOR head of the payload */ \
+        /* The payload -- add this in yourself */ \
+    2 + /* CBOR head of signature */ \
+    64  /* T_COSE_EC_P256_SIG_SIZE */
+
+#define T_COSE_MINI_SIGN_SIZE_OVERHEAD_ES384 \
+    1 + /* Open the array */ \
+    6 + /* The header parameters */ \
+    3 + /* The CBOR head of the payload */ \
+        /* The payload -- add this in yourself */ \
+    2 + /* CBOR head of signature */ \
+    96 /* T_COSE_EC_P384_SIG_SIZE */
+
+#define T_COSE_MINI_SIGN_SIZE_OVERHEAD_ES512 \
+    1 + /* Open the array */ \
+    6 + /* The header parameters */ \
+    3 + /* The CBOR head of the payload */ \
+        /* The payload -- add this in yourself */ \
+    2 + /* CBOR head of signature */ \
+    132 /* T_COSE_EC_P512_SIG_SIZE */
+
+
+/**
+ * @brief Create a COSE_Sign1 with fixed algorithm and no header parameters.
+ *
+ * @param[in] payload         The payload to sign.
+ * @param[in] signing_key     The key to sign with.
+ * @param[in] output_buffer   The buffer where the COSE_Sign1 is written.
+ * @param[out] output         Pointer and length of the completed COSE_Sign1.
+ *
+ * @return  T_COSE_ERR_TOO_LONG The payload length is > UINT16_MAX
+ *          T_COSE_ERR_TOO_SMALL  The output_buffer is too small for the
+ *                                payload.
+ *          Other errors related to invocation of the crypto algorithms.
+ *
+ * This signs a payload to make a COSE_Sign1 in the simplest possible
+ * way. The object code for this is very small. This is achieved by
+ * fixing the algorithm at compile time, not allowing any header
+ * parameters but the signing algorithm and limiting the payload size
+ * to \c UINT16_MAX. The default algorithm is COSE ES256 (EC with the
+ * secp256r1 curve).
+ *
+ * See t_cose_sign1_sign() for full-featured signing.
+ *
+ * The inputs are a payload to sign and a signing key. The signing key
+ * is a handle or pointer to a key usable with the crypto library this
+ * is linked against (probably OpenSSL or Mbed TLS). The key
+ * set up is the same as in the t_cose examples.
+ *
+ * An output buffer must be given sized large enough to hold the
+ * COSE_Sign1 message produced. The size of this is \ref
+ * T_COSE_MINI_SIGN_SIZE_OVERHEAD_ES256 larger than the payload. If
+ * \c output_buffer is too small, an error will be returned.
+ *
+ * This does NOT need to link with a CBOR encoder. It does need to
+ * link with a cryptographic library. OpenSSL and Mbed TLS are
+ * supported. It uses the t_cose_crypto.h layer to interface with the
+ * cryptographic library. It should be easy adapt this to other
+ * cryptographic libraries.
+ *
+ * ES384 and ES512 are also supported, but you have to modify the
+ * source to switch to one of them. The source could be further
+ * modified to support RSA.
+ *
+ * See comments in the source code to change the algorithm and
+ * discussion about other modifications.
+ */
+enum t_cose_err_t
+t_cose_mini_sign1_sign(struct q_useful_buf_c  payload,
+                       struct t_cose_key      signing_key,
+                       struct q_useful_buf    output_buffer,
+                       struct q_useful_buf_c *output);
+
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* __T_COSE_MINI_SIGN_H__ */