A minimal COSE_Sign1 verifier

Makefile.psa

@@ -64,7 +64,7 @@ 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_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_sign_mini_verify.o
 
 .PHONY: all install install_headers install_so uninstall clean
 

examples/t_cose_basic_example_psa.c

@@ -14,6 +14,8 @@
 #include "t_cose/t_cose_sign1_verify.h"
 #include "t_cose/q_useful_buf.h"
 
+#include "t_cose/t_cose_sign_mini_verify.h"
+
 #include "psa/crypto.h"
 
 #include <stdio.h>
@@ -595,11 +597,82 @@ int two_step_sign_example(void)
     return (int)return_value;
 }
 
+
+void mini()
+{
+    struct t_cose_sign1_sign_ctx   sign_ctx;
+    enum t_cose_err_t              return_value;
+    Q_USEFUL_BUF_MAKE_STACK_UB(    signed_cose_buffer, 300);
+    struct q_useful_buf_c          signed_cose;
+    struct q_useful_buf_c          payload;
+    struct t_cose_key              key_pair;
+
+
+    return_value = make_psa_ecdsa_key_pair(T_COSE_ALGORITHM_ES384, &key_pair);
+
+    /* ------   Initialize for signing    ------
+       *
+       * Initialize the signing context by telling it the signing
+       * algorithm and signing options. No options are set here hence
+       * the 0 value.
+       *
+       * Set up the signing key and kid (key ID). No kid is passed here
+       * hence the NULL_Q_USEFUL_BUF_C.
+       */
+
+      t_cose_sign1_sign_init(&sign_ctx, T_COSE_OPT_OMIT_CBOR_TAG, T_COSE_ALGORITHM_ES384);
+
+      t_cose_sign1_set_signing_key(&sign_ctx, key_pair,  NULL_Q_USEFUL_BUF_C);
+
+      printf("Initialized t_cose and configured signing key\n");
+
+
+      /* ------   Sign    ------
+       *
+       * This performs encoding of the headers, the signing and formatting
+       * in one shot.
+       *
+       * With this API the payload ends up in memory twice, once as the
+       * input and once in the output. If the payload is large, this
+       * needs about double the size of the payload to work.
+       */
+      return_value = t_cose_sign1_sign(/* The context set up with signing key */
+                                       &sign_ctx,
+                                       /* Pointer and length of payload to be
+                                        * signed.
+                                        */
+                                       Q_USEFUL_BUF_FROM_SZ_LITERAL("XX"),
+                                       /* Non-const pointer and length of the
+                                        * buffer where the completed output is
+                                        * written to. The length here is that
+                                        * of the whole buffer.
+                                        */
+                                       signed_cose_buffer,
+                                       /* Const pointer and actual length of
+                                        * the completed, signed and encoded
+                                        * COSE_Sign1 message. This points
+                                        * into the output buffer and has the
+                                        * lifetime of the output buffer.
+                                        */
+                                       &signed_cose);
+
+
+
+    return_value =
+    t_cose_sign1_mini_verify(signed_cose,
+                             key_pair,
+                             &payload);
+
+
+}
+
 int main(int argc, const char * argv[])
 {
     (void)argc; /* Avoid unused parameter error */
     (void)argv;
 
+    mini();
+
     one_step_sign_example();
     two_step_sign_example();
 }

inc/t_cose/t_cose_sign_mini_verify.h

@@ -0,0 +1,80 @@
+/*
+ * t_cose_sign_mini_verify.h
+ *
+ * Copyright 2022-2023, Laurence Lundblade
+ *
+ * Created by Laurence Lundblade on 8/17/22.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
+ * See BSD-3-Clause license in README.md
+ */
+
+#ifndef t_cose_sign_mini_verify_h
+#define t_cose_sign_mini_verify_h
+
+#include "t_cose/q_useful_buf.h"
+#include "t_cose/t_cose_common.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+
+/*
+ * The algorithm is set at compile time for mini sign and can't be
+ * changed.  Only one algorithm is
+ * supported at a time. Define one of these to configure the algorithm. If
+ * none are configured, ES256 is selected.
+
+#define T_COSE_MINI_VERIFY_SELECT_ES256
+#define T_COSE_MINI_VERIFY_SELECT_ES384
+#define T_COSE_MINI_VERIFY_SELECT_ES512
+*/
+
+#if !defined(T_COSE_MINI_VERIFY_SELECT_ES256) && \
+    !defined(T_COSE_MINI_VERIFY_SELECT_ES384) && \
+    !defined(T_COSE_MINI_VERIFY_SELECT_ES512)
+#define T_COSE_MINI_VERIFY_SELECT_ES256
+#endif
+
+
+/**
+ * @brief Minature verification of COSE_Sign1
+ *
+ * @param[in] cose_sign1   The COSE_Sign1 to verify.
+ * @param[in] verification_key  The verification key.
+ * @param[out] payload   Pointer and length of verified payload.
+ *
+ * @return The error result.
+ *
+ * This is an implementation of \c COSE_Sign1 verification
+ * with very small, near  minimun code size. It has
+ * almost no external dependency, except a crypto library,
+ * not even a CBOR library.
+ *
+ * Only one algorithm is supported at a time. If the
+ * input \c COSE_Sign1 doesn't use that algorithm
+ * an error is returned.
+ *
+ * There is no header decoding to retrieve a key ID, so
+ * identification of the key must be by some other means.
+ *
+ * It simply checks that the algorithm header parameter
+ * matches what it compiled to support, decodes
+ * the payload and the signature, verifies the
+ * signature and returns the verified payload.
+ *
+ * This has very crude error reporting in order to keep
+ * the code size small. Success is always success and failure
+ * always failure, but the failure reported might be misleading
+ * as to the actual reason for the failure.
+ */
+enum t_cose_err_t
+t_cose_sign1_mini_verify(struct q_useful_buf_c   cose_sign1,
+                         struct t_cose_key       verification_key,
+                         struct q_useful_buf_c  *payload);
+
+
+
+#endif /* t_cose_sign_mini_verify_h */