Add SipHash example

SipHash-2-4 one-shot 64/128-bit MACs and the incremental API, checked
against the reference implementation's test vector.

crypto/siphash/Makefile

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+CC=gcc
+WOLFSSL_INSTALL_DIR=/usr/local
+CFLAGS=-Wall -I$(WOLFSSL_INSTALL_DIR)/include
+LIBS=-L$(WOLFSSL_INSTALL_DIR)/lib -lwolfssl -lm
+
+siphash-mac: siphash-mac.o
+	$(CC) -o $@ $^ $(CFLAGS) $(LIBS)
+
+.PHONY: clean check
+
+clean:
+	rm -f *.o siphash-mac
+
+check: siphash-mac
+	out=$$(./siphash-mac) && printf '%s' "$$out" | grep -q 'Incremental MAC matches one-shot MAC'
+	@echo "PASS: crypto-siphash checks"

crypto/siphash/README.md

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+# wolfSSL SipHash Example
+
+Demonstrates SipHash-2-4 keyed MACs with the `wc_SipHash*` API: one-shot
+64-bit and 128-bit tags plus the incremental Init/Update/Final interface,
+checked against the reference implementation's test vector.
+
+SipHash is a fast keyed pseudorandom function for short inputs. Typical uses
+are hash-table flooding protection and lightweight per-packet authentication;
+it is not a general-purpose collision-resistant hash.
+
+## Building wolfSSL
+
+```
+./configure --enable-siphash
+make
+sudo make install
+```
+
+## Building and running the example
+
+```
+make
+./siphash-mac
+```

crypto/siphash/siphash-mac.c

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+/* siphash-mac.c
+ *
+ * Copyright (C) 2006-2026 wolfSSL Inc.
+ *
+ * This file is part of wolfSSL. (formerly known as CyaSSL)
+ *
+ * wolfSSL is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * wolfSSL is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA
+ */
+
+/* Example of SipHash-2-4 as a short-output keyed MAC.
+ *
+ * SipHash is designed for short inputs (hash table keys, network packet
+ * authentication) where a fast 64- or 128-bit keyed MAC is enough. */
+
+#include <stdio.h>
+#include <string.h>
+
+#include <wolfssl/options.h>
+#include <wolfssl/wolfcrypt/settings.h>
+#include <wolfssl/wolfcrypt/siphash.h>
+
+#ifdef WOLFSSL_SIPHASH
+
+/* Reference test vector from https://github.com/veorq/SipHash: key 00..0f,
+ * message 00..0e, 8-byte output. */
+static const byte kat_key[SIPHASH_KEY_SIZE] = {
+    0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
+    0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f
+};
+static const byte kat_msg[15] = {
+    0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
+    0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e
+};
+static const byte kat_mac[SIPHASH_MAC_SIZE_8] = {
+    0xe5, 0x45, 0xbe, 0x49, 0x61, 0xca, 0x29, 0xa1
+};
+
+static void print_hex(const char* label, const byte* data, word32 len)
+{
+    word32 i;
+
+    printf("%s: ", label);
+    for (i = 0; i < len; i++)
+        printf("%02x", data[i]);
+    printf("\n");
+}
+
+int main(void)
+{
+    int     ret;
+    SipHash sipHash;
+    byte    mac8[SIPHASH_MAC_SIZE_8];
+    byte    mac16[SIPHASH_MAC_SIZE_16];
+
+    /* One-shot with an 8-byte tag, checked against the reference vector. */
+    ret = wc_SipHash(kat_key, kat_msg, sizeof(kat_msg), mac8,
+                     SIPHASH_MAC_SIZE_8);
+    if (ret != 0) {
+        printf("wc_SipHash failed %d\n", ret);
+        return 1;
+    }
+    print_hex("SipHash-2-4 64-bit ", mac8, sizeof(mac8));
+    if (memcmp(mac8, kat_mac, sizeof(kat_mac)) != 0) {
+        printf("MAC does not match reference test vector!\n");
+        return 1;
+    }
+    printf("MAC matches reference test vector\n");
+
+    /* One-shot with a 16-byte tag. */
+    ret = wc_SipHash(kat_key, kat_msg, sizeof(kat_msg), mac16,
+                     SIPHASH_MAC_SIZE_16);
+    if (ret != 0) {
+        printf("wc_SipHash failed %d\n", ret);
+        return 1;
+    }
+    print_hex("SipHash-2-4 128-bit", mac16, sizeof(mac16));
+
+    /* Incremental API produces the same tag as one-shot. */
+    ret = wc_InitSipHash(&sipHash, kat_key, SIPHASH_MAC_SIZE_8);
+    if (ret == 0)
+        ret = wc_SipHashUpdate(&sipHash, kat_msg, 8);
+    if (ret == 0)
+        ret = wc_SipHashUpdate(&sipHash, kat_msg + 8, sizeof(kat_msg) - 8);
+    if (ret == 0)
+        ret = wc_SipHashFinal(&sipHash, mac8, SIPHASH_MAC_SIZE_8);
+    if (ret != 0) {
+        printf("incremental SipHash failed %d\n", ret);
+        return 1;
+    }
+    if (memcmp(mac8, kat_mac, sizeof(kat_mac)) != 0) {
+        printf("Incremental MAC does not match one-shot MAC!\n");
+        return 1;
+    }
+    printf("Incremental MAC matches one-shot MAC\n");
+
+    return 0;
+}
+
+#else
+
+int main(void)
+{
+    printf("Please build wolfSSL with ./configure --enable-siphash\n");
+    return 0;
+}
+
+#endif /* WOLFSSL_SIPHASH */