lib/crypto: tests: Add KUnit tests for NH

Add some simple KUnit tests for the nh() function.

These replace the test coverage which will be lost by removing the
nhpoly1305 crypto_shash.

Note that the NH code also continues to be tested indirectly as well,
via the tests for the "adiantum(xchacha12,aes)" crypto_skcipher.

Link: https://lore.kernel.org/r/20251211011846.8179-3-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>

scripts/crypto/gen-hash-testvecs.py

@@ -184,6 +184,44 @@ def gen_additional_blake2_testvecs(alg):
             f'{alg}_keyed_testvec_consolidated[{alg_digest_size_const(alg)}]',
             compute_hash(alg, hashes))
 
+def nh_extract_int(bytestr, pos, length):
+    assert pos % 8 == 0 and length % 8 == 0
+    return int.from_bytes(bytestr[pos//8 : pos//8 + length//8], byteorder='little')
+
+# The NH "almost-universal hash function" used in Adiantum.  This is a
+# straightforward translation of the pseudocode from Section 6.3 of the Adiantum
+# paper (https://eprint.iacr.org/2018/720.pdf), except the outer loop is omitted
+# because we assume len(msg) <= 1024.  (The kernel's nh() function is only
+# expected to handle up to 1024 bytes; it's just called repeatedly as needed.)
+def nh(key, msg):
+    (w, s, r, u) = (32, 2, 4, 8192)
+    l = 8 * len(msg)
+    assert l <= u
+    assert l % (2*s*w) == 0
+    h = bytes()
+    for i in range(0, 2*s*w*r, 2*s*w):
+        p = 0
+        for j in range(0, l, 2*s*w):
+            for k in range(0, w*s, w):
+                a0 = nh_extract_int(key, i + j + k, w)
+                a1 = nh_extract_int(key, i + j + k + s*w, w)
+                b0 = nh_extract_int(msg, j + k, w)
+                b1 = nh_extract_int(msg, j + k + s*w, w)
+                p += ((a0 + b0) % 2**w) * ((a1 + b1) % 2**w)
+        h += (p % 2**64).to_bytes(8, byteorder='little')
+    return h
+
+def gen_nh_testvecs():
+    NH_KEY_BYTES = 1072
+    NH_MESSAGE_BYTES = 1024
+    key = rand_bytes(NH_KEY_BYTES)
+    msg = rand_bytes(NH_MESSAGE_BYTES)
+    print_static_u8_array_definition('nh_test_key[NH_KEY_BYTES]', key)
+    print_static_u8_array_definition('nh_test_msg[NH_MESSAGE_BYTES]', msg)
+    for length in [16, 96, 256, 1024]:
+        print_static_u8_array_definition(f'nh_test_val{length}[NH_HASH_BYTES]',
+                                         nh(key, msg[:length]))
+
 def gen_additional_poly1305_testvecs():
     key = b'\xff' * POLY1305_KEY_SIZE
     data = b''
@@ -217,6 +255,8 @@ print(f'/* This file was generated by: {sys.argv[0]} {" ".join(sys.argv[1:])} */
 if alg.startswith('blake2'):
     gen_unkeyed_testvecs(alg)
     gen_additional_blake2_testvecs(alg)
+elif alg == 'nh':
+    gen_nh_testvecs()
 elif alg == 'poly1305':
     gen_unkeyed_testvecs(alg)
     gen_additional_poly1305_testvecs()