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diff --git a/src/include/ipxe/des.h b/src/include/ipxe/des.h
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+#ifndef _IPXE_DES_H
+#define _IPXE_DES_H
+
+/** @file
+ *
+ * DES algorithm
+ *
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
+
+#include <ipxe/crypto.h>
+
+/** A DES 32-bit dword value
+ *
+ * DES views data as 64-bit big-endian values, typically handled as a
+ * most-significant "left" half and a least-significant "right" half.
+ */
+union des_dword {
+	/** Raw bytes */
+	uint8_t byte[4];
+	/** 32-bit big-endian dword */
+	uint32_t dword;
+};
+
+/** A DES 64-bit block */
+union des_block {
+	/** Raw bytes */
+	uint8_t byte[8];
+	/** 32-bit big-endian dwords */
+	uint32_t dword[2];
+	/** Named left and right halves */
+	struct {
+		/** Left (most significant) half */
+		union des_dword left;
+		/** Right (least significant) half */
+		union des_dword right;
+	};
+	/** Named "C" and "D" halves */
+	struct {
+		/** "C" (most significant) half */
+		union des_dword c;
+		/** "D" (least significant) half */
+		union des_dword d;
+	};
+};
+
+/** DES blocksize */
+#define DES_BLOCKSIZE sizeof ( union des_block )
+
+/** A DES round key
+ *
+ * A DES round key is a 48-bit value, consumed as 8 groups of 6 bits.
+ * We store these as 8 separate bytes, for simplicity of consumption.
+ */
+union des_round_key {
+	/** Raw bytes */
+	uint8_t byte[8];
+	/** 32-bit big-endian dwords */
+	uint32_t dword[2];
+	/** 6-bit step key byte
+	 *
+	 * There are 8 steps within a DES round (one step per S-box).
+	 * Each step requires six bits of the round key.
+	 *
+	 * As an optimisation, we store the least significant of the 6
+	 * bits in the sign bit of a signed 8-bit value, and the
+	 * remaining 5 bits in the least significant 5 bits of the
+	 * 8-bit value.  See the comments in des_sbox() for further
+	 * details.
+	 */
+	int8_t step[8];
+};
+
+/** Number of DES rounds */
+#define DES_ROUNDS 16
+
+/** DES context */
+struct des_context {
+	/** Round keys */
+	union des_round_key rkey[DES_ROUNDS];
+};
+
+/** DES context size */
+#define DES_CTX_SIZE sizeof ( struct des_context )
+
+extern struct cipher_algorithm des_algorithm;
+extern struct cipher_algorithm des_ecb_algorithm;
+extern struct cipher_algorithm des_cbc_algorithm;
+
+#endif /* _IPXE_DES_H */