backports: add signature verification code

Uh, this was awful. Because the crypto/ things are completely
impossible to backport, I've actually implemented this by using
mbedtls and embedding the relevant functions it has...

The mbedtls code is taken from mbedtls version 2.6.0 and only
minimally modified (mostly to remove <string.h> and similar).

Signed-off-by: Johannes Berg <johannes.berg@intel.com>

1 files changed, 140 insertions, 0 deletions

diff --git a/backport/compat/verification/mbedtls/sha256.h b/backport/compat/verification/mbedtls/sha256.h
new file mode 100644
index 00000000..68223f0b
--- /dev/null
+++ b/backport/compat/verification/mbedtls/sha256.h
@@ -0,0 +1,140 @@
+/**
+ * \file sha256.h
+ *
+ * \brief SHA-224 and SHA-256 cryptographic hash function
+ *
+ *  Copyright (C) 2006-2015, ARM Limited, All Rights Reserved
+ *  SPDX-License-Identifier: GPL-2.0
+ *
+ *  This program is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation; either version 2 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License along
+ *  with this program; if not, write to the Free Software Foundation, Inc.,
+ *  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ *  This file is part of mbed TLS (https://tls.mbed.org)
+ */
+#ifndef MBEDTLS_SHA256_H
+#define MBEDTLS_SHA256_H
+
+#if !defined(MBEDTLS_CONFIG_FILE)
+#include "config.h"
+#else
+#include MBEDTLS_CONFIG_FILE
+#endif
+
+#if !defined(MBEDTLS_SHA256_ALT)
+// Regular implementation
+//
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * \brief          SHA-256 context structure
+ */
+typedef struct
+{
+    uint32_t total[2];          /*!< number of bytes processed  */
+    uint32_t state[8];          /*!< intermediate digest state  */
+    unsigned char buffer[64];   /*!< data block being processed */
+    int is224;                  /*!< 0 => SHA-256, else SHA-224 */
+}
+mbedtls_sha256_context;
+
+/**
+ * \brief          Initialize SHA-256 context
+ *
+ * \param ctx      SHA-256 context to be initialized
+ */
+void mbedtls_sha256_init( mbedtls_sha256_context *ctx );
+
+/**
+ * \brief          Clear SHA-256 context
+ *
+ * \param ctx      SHA-256 context to be cleared
+ */
+void mbedtls_sha256_free( mbedtls_sha256_context *ctx );
+
+/**
+ * \brief          Clone (the state of) a SHA-256 context
+ *
+ * \param dst      The destination context
+ * \param src      The context to be cloned
+ */
+void mbedtls_sha256_clone( mbedtls_sha256_context *dst,
+                           const mbedtls_sha256_context *src );
+
+/**
+ * \brief          SHA-256 context setup
+ *
+ * \param ctx      context to be initialized
+ * \param is224    0 = use SHA256, 1 = use SHA224
+ */
+void mbedtls_sha256_starts( mbedtls_sha256_context *ctx, int is224 );
+
+/**
+ * \brief          SHA-256 process buffer
+ *
+ * \param ctx      SHA-256 context
+ * \param input    buffer holding the  data
+ * \param ilen     length of the input data
+ */
+void mbedtls_sha256_update( mbedtls_sha256_context *ctx, const unsigned char *input,
+                    size_t ilen );
+
+/**
+ * \brief          SHA-256 final digest
+ *
+ * \param ctx      SHA-256 context
+ * \param output   SHA-224/256 checksum result
+ */
+void mbedtls_sha256_finish( mbedtls_sha256_context *ctx, unsigned char output[32] );
+
+/* Internal use */
+void mbedtls_sha256_process( mbedtls_sha256_context *ctx, const unsigned char data[64] );
+
+#ifdef __cplusplus
+}
+#endif
+
+#else  /* MBEDTLS_SHA256_ALT */
+#include "sha256_alt.h"
+#endif /* MBEDTLS_SHA256_ALT */
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * \brief          Output = SHA-256( input buffer )
+ *
+ * \param input    buffer holding the  data
+ * \param ilen     length of the input data
+ * \param output   SHA-224/256 checksum result
+ * \param is224    0 = use SHA256, 1 = use SHA224
+ */
+void mbedtls_sha256( const unsigned char *input, size_t ilen,
+           unsigned char output[32], int is224 );
+
+/**
+ * \brief          Checkup routine
+ *
+ * \return         0 if successful, or 1 if the test failed
+ */
+int mbedtls_sha256_self_test( int verbose );
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* mbedtls_sha256.h */