lib/crypto: nh: Add NH library

Add support for the NH "almost-universal hash function" to lib/crypto/,
specifically the variant of NH used in Adiantum.

This will replace the need for the "nhpoly1305" crypto_shash algorithm.
All the implementations of "nhpoly1305" use architecture-optimized code
only for the NH stage; they just use the generic C Poly1305 code for the
Poly1305 stage.  We can achieve the same result in a simpler way using
an (architecture-optimized) nh() function combined with code in
crypto/adiantum.c that passes the results to the Poly1305 library.

This commit begins this cleanup by adding the nh() function.  The code
is derived from crypto/nhpoly1305.c and include/crypto/nhpoly1305.h.

Link: https://lore.kernel.org/r/20251211011846.8179-2-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>

1 files changed, 52 insertions, 0 deletions

diff --git a/include/crypto/nh.h b/include/crypto/nh.h
new file mode 100644
index 000000000000..465e85bf203f
--- /dev/null
+++ b/include/crypto/nh.h
@@ -0,0 +1,52 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * NH hash function for Adiantum
+ */
+
+#ifndef _CRYPTO_NH_H
+#define _CRYPTO_NH_H
+
+#include <linux/types.h>
+
+/* NH parameterization: */
+
+/* Endianness: little */
+/* Word size: 32 bits (works well on NEON, SSE2, AVX2) */
+
+/* Stride: 2 words (optimal on ARM32 NEON; works okay on other CPUs too) */
+#define NH_PAIR_STRIDE		2
+#define NH_MESSAGE_UNIT		(NH_PAIR_STRIDE * 2 * sizeof(u32))
+
+/* Num passes (Toeplitz iteration count): 4, to give ε = 2^{-128} */
+#define NH_NUM_PASSES		4
+#define NH_HASH_BYTES		(NH_NUM_PASSES * sizeof(u64))
+
+/* Max message size: 1024 bytes (32x compression factor) */
+#define NH_NUM_STRIDES		64
+#define NH_MESSAGE_WORDS	(NH_PAIR_STRIDE * 2 * NH_NUM_STRIDES)
+#define NH_MESSAGE_BYTES	(NH_MESSAGE_WORDS * sizeof(u32))
+#define NH_KEY_WORDS		(NH_MESSAGE_WORDS + \
+				 NH_PAIR_STRIDE * 2 * (NH_NUM_PASSES - 1))
+#define NH_KEY_BYTES		(NH_KEY_WORDS * sizeof(u32))
+
+/**
+ * nh() - NH hash function for Adiantum
+ * @key: The key.  @message_len + 48 bytes of it are used.  This is NH_KEY_BYTES
+ *	 if @message_len has its maximum length of NH_MESSAGE_BYTES.
+ * @message: The message
+ * @message_len: The message length in bytes.  Must be a multiple of 16
+ *		 (NH_MESSAGE_UNIT) and at most 1024 (NH_MESSAGE_BYTES).
+ * @hash: (output) The resulting hash value
+ *
+ * Note: the pseudocode for NH in the Adiantum paper iterates over 1024-byte
+ * segments of the message, computes a 32-byte hash for each, and returns all
+ * the hashes concatenated together.  In contrast, this function just hashes one
+ * segment and returns one hash.  It's the caller's responsibility to call this
+ * function for each 1024-byte segment and collect all the hashes.
+ *
+ * Context: Any context.
+ */
+void nh(const u32 *key, const u8 *message, size_t message_len,
+	__le64 hash[NH_NUM_PASSES]);
+
+#endif /* _CRYPTO_NH_H */