Attest: Add attestation core, COSE library & tests
Adds core library for creating EAT (draft-mandyam-eat-01)
format attestations. Adds t_cose an implementation of
COSE_Sign1 as defined in RFC 8152 section 4.2. Adds
basic test for creation of EAT format attestations.
Change-Id: I1ff8339edc55d50bd7639e42539844f2394280dc
Signed-off-by: Laurence Lundblade <lgl@securitytheory.com>
diff --git a/lib/t_cose/src/t_cose_util.h b/lib/t_cose/src/t_cose_util.h
new file mode 100644
index 0000000..7b39dc3
--- /dev/null
+++ b/lib/t_cose/src/t_cose_util.h
@@ -0,0 +1,126 @@
+/*
+ * t_cose_util.h
+ *
+ * Copyright 2019, Laurence Lundblade
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
+ * See BSD-3-Clause license in README.mdE.
+ */
+
+
+#ifndef __T_COSE_UTIL_H__
+#define __T_COSE_UTIL_H__
+
+#include <stdint.h>
+#include "useful_buf.h"
+#include "t_cose_common.h"
+
+/**
+ * \file t_cose_util.h
+ *
+ * \brief Utility functions used internally by the t_cose implementation.
+ *
+ */
+
+
+/**
+ * \brief Return hash algorithm ID from a signature algorithm ID
+ *
+ * \param[in] cose_sig_alg_id A COSE signature algorithm identifier.
+ *
+ * \return \c INT32_MAX when the signature algorithm ID is not known.
+ *
+ * This works off of algorithm identifiers defined in the [IANA COSE
+ * Registry] (https://www.iana.org/assignments/cose/cose.xhtml).
+ * Corresponding local integer constants are defined in
+ * t_cose_defines.h.
+ *
+ * COSE signing algorithms are the combination of public key
+ * algorithm, curve, key size, hash algorithm and hash size. They are
+ * simple integers making them convenient for direct use in code.
+ *
+ * This function returns an identifier for only the hash algorithm
+ * from the combined identifier.
+ *
+ * If the needed algorithm identifiers are not in the IANA registry,
+ * they can be added to it. This will take some time and work. It is
+ * also fine to use algorithms in the proprietary space.
+ */
+int32_t hash_alg_id_from_sig_alg_id(int32_t cose_sig_alg_id);
+
+
+/**
+ * \brief Create the hash of the to-be-signed (TBS) bytes for COSE.
+ *
+ * \param[in] cose_alg_id The COSE signing algorithm ID. Used to
+ * determine which hash function to use.
+ * \param[in] buffer_for_hash Pointer and length of buffer into which
+ * the resulting hash is put.
+ * \param[out] hash Pointer and length of the
+ * resulting hash.
+ * \param[in] protected_headers The CBOR encoded protected headers.
+ * \param[in] payload The CBOR encoded payload
+ *
+ * \return This returns one of the error codes defined by \ref t_cose_err_t.
+ *
+ * \retval T_COSE_ERR_SIG_STRUCT
+ * Most likely this is because the protected_headers passed in
+ * is larger than \ref T_COSE_SIGN1_MAX_PROT_HEADER.
+ * \retval T_COSE_ERR_UNSUPPORTED_HASH
+ * If the hash algorithm is not known.
+ * \retval T_COSE_ERR_HASH_GENERAL_FAIL
+ * In case of some general hash failure.
+ *
+ * The input to the public key signature algorithm in COSE is the hash
+ * of a CBOR encoded structure containing the protected headers
+ * algorithm ID and a few other things. This formats that structure
+ * and computes the hash of it. These are known as the to-be-signed or
+ * "TBS" bytes.
+ */
+enum t_cose_err_t create_tbs_hash(int32_t cose_alg_id,
+ struct useful_buf buffer_for_hash,
+ struct useful_buf_c *hash,
+ struct useful_buf_c protected_headers,
+ struct useful_buf_c payload);
+
+
+/**
+ * Size of the key returned by get_short_circuit_kid(). It is always
+ * this size.
+ */
+#define T_COSE_SHORT_CIRCUIT_KID_SIZE 32
+
+
+/**
+ * \brief Get the special kid for short-circuit signing.
+ *
+ * \param[in] buffer_for_kid Pointer and length of buffer into which
+ * the resulting hash is put. It should
+ * always be at least \ref
+ * T_COSE_SHORT_CIRCUIT_KID_SIZE.
+ * \param[out] kid Pointer and length of the returned kid.
+ *
+ * \retval T_COSE_SUCCESS
+ * The kid was returned.
+ * \retval T_COSE_ERR_KEY_BUFFER_SIZE
+ * \c buffer_for_kid is too small
+ *
+ * This always returns the same key ID. It always indicates
+ * short-circuit signing. It is OK to hard code this as the
+ * probability of collision with this ID is extremely low and the same
+ * as for collision between any two key IDs (kids) of any sort.
+ *
+ * This is the value of the kid.
+ *
+ * 0xef, 0x95, 0x4b, 0x4b, 0xd9, 0xbd, 0xf6, 0x70,
+ * 0xd0, 0x33, 0x60, 0x82, 0xf5, 0xef, 0x15, 0x2a,
+ * 0xf8, 0xf3, 0x5b, 0x6a, 0x6c, 0x00, 0xef, 0xa6,
+ * 0xa9, 0xa7, 0x1f, 0x49, 0x51, 0x7e, 0x18, 0xc6
+ *
+ */
+enum t_cose_err_t
+get_short_circuit_kid(struct useful_buf buffer_for_kid,
+ struct useful_buf_c *kid);
+
+#endif /* __T_COSE_UTIL_H__ */