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+/*
+ * cifra - embedded cryptography library
+ * Written in 2014 by Joseph Birr-Pixton <jpixton@gmail.com>
+ *
+ * To the extent possible under law, the author(s) have dedicated all
+ * copyright and related and neighboring rights to this software to the
+ * public domain worldwide. This software is distributed without any
+ * warranty.
+ *
+ * You should have received a copy of the CC0 Public Domain Dedication
+ * along with this software. If not, see
+ * <http://creativecommons.org/publicdomain/zero/1.0/>.
+ */
+
+#ifndef SHA2_H
+#define SHA2_H
+
+#include <stddef.h>
+#include <stdint.h>
+
+#include "chash.h"
+
+/**
+ * SHA224/SHA256
+ * =============
+ */
+
+/* .. c:macro:: CF_SHA256_HASHSZ
+ * The output size of SHA256: 32 bytes. */
+#define CF_SHA256_HASHSZ 32
+
+/* .. c:macro:: CF_SHA256_BLOCKSZ
+ * The block size of SHA256: 64 bytes. */
+#define CF_SHA256_BLOCKSZ 64
+
+/* .. c:type:: cf_sha256_context
+ * Incremental SHA256 hashing context.
+ *
+ * .. c:member:: cf_sha256_context.H
+ * Intermediate values.
+ *
+ * .. c:member:: cf_sha256_context.partial
+ * Unprocessed input.
+ *
+ * .. c:member:: cf_sha256_context.npartial
+ * Number of bytes of unprocessed input.
+ *
+ * .. c:member:: cf_sha256_context.blocks
+ * Number of full blocks processed.
+ */
+typedef struct
+{
+  uint32_t H[8];                      /* State. */
+  uint8_t partial[CF_SHA256_BLOCKSZ]; /* Partial block of input. */
+  uint32_t blocks;                    /* Number of full blocks processed into H. */
+  size_t npartial;                    /* Number of bytes in prefix of partial. */
+} cf_sha256_context;
+
+/* .. c:function:: $DECL
+ * Sets up `ctx` ready to hash a new message.
+ */
+extern void cf_sha256_init(cf_sha256_context *ctx);
+
+/* .. c:function:: $DECL
+ * Hashes `nbytes` at `data`.  Copies the data if there isn't enough to make
+ * a full block.
+ */
+extern void cf_sha256_update(cf_sha256_context *ctx, const void *data, size_t nbytes);
+
+/* .. c:function:: $DECL
+ * Finishes the hash operation, writing `CF_SHA256_HASHSZ` bytes to `hash`.
+ *
+ * This leaves `ctx` unchanged.
+ */
+extern void cf_sha256_digest(const cf_sha256_context *ctx, uint8_t hash[CF_SHA256_HASHSZ]);
+
+/* .. c:function:: $DECL
+ * Finishes the hash operation, writing `CF_SHA256_HASHSZ` bytes to `hash`.
+ *
+ * This destroys `ctx`, but uses less stack than :c:func:`cf_sha256_digest`.
+ */
+extern void cf_sha256_digest_final(cf_sha256_context *ctx, uint8_t hash[CF_SHA256_HASHSZ]);
+
+/* .. c:var:: cf_sha256
+ * Abstract interface to SHA256.  See :c:type:`cf_chash` for more information.
+ */
+extern const cf_chash cf_sha256;
+
+#endif