[crypto] Add SHA-256 algorithm

This implementation has been verified using the NIST SHA-256 test vectors.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/include/ipxe/sha256.h

@@ -0,0 +1,73 @@
+#ifndef _IPXE_SHA256_H
+#define _IPXE_SHA256_H
+
+/** @file
+ *
+ * SHA-256 algorithm
+ *
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER );
+
+#include <stdint.h>
+#include <ipxe/crypto.h>
+
+/** An SHA-256 digest */
+struct sha256_digest {
+	/** Hash output */
+	uint32_t h[8];
+};
+
+/** An SHA-256 data block */
+union sha256_block {
+	/** Raw bytes */
+	uint8_t byte[64];
+	/** Raw dwords */
+	uint32_t dword[16];
+	/** Final block structure */
+	struct {
+		/** Padding */
+		uint8_t pad[56];
+		/** Length in bits */
+		uint64_t len;
+	} final;
+};
+
+/** SHA-256 digest and data block
+ *
+ * The order of fields within this structure is designed to minimise
+ * code size.
+ */
+struct sha256_digest_data {
+	/** Digest of data already processed */
+	struct sha256_digest digest;
+	/** Accumulated data */
+	union sha256_block data;
+} __attribute__ (( packed ));
+
+/** SHA-256 digest and data block */
+union sha256_digest_data_dwords {
+	/** Digest and data block */
+	struct sha256_digest_data dd;
+	/** Raw dwords */
+	uint32_t dword[ sizeof ( struct sha256_digest_data ) /
+			sizeof ( uint32_t ) ];
+};
+
+/** An SHA-256 context */
+struct sha256_context {
+	/** Amount of accumulated data */
+	size_t len;
+	/** Digest and accumulated data */
+	union sha256_digest_data_dwords ddd;
+} __attribute__ (( packed ));
+
+/** SHA-256 context size */
+#define SHA256_CTX_SIZE sizeof ( struct sha256_context )
+
+/** SHA-256 digest size */
+#define SHA256_DIGEST_SIZE sizeof ( struct sha256_digest )
+
+extern struct digest_algorithm sha256_algorithm;
+
+#endif /* _IPXE_SHA256_H */