Add SHA256 HMAC

SPHINCS+ need HMAC

Author: guanzhi

include/gmssl/sha2.h

@@ -1,5 +1,5 @@
 /*
- *  Copyright 2014-2024 The GmSSL Project. All Rights Reserved.
+ *  Copyright 2014-2026 The GmSSL Project. All Rights Reserved.
  *
  *  Licensed under the Apache License, Version 2.0 (the License); you may
  *  not use this file except in compliance with the License.
@@ -88,6 +88,18 @@ void sha512_update(SHA512_CTX *ctx, const uint8_t* data, size_t datalen);
 void sha512_finish(SHA512_CTX *ctx, uint8_t dgst[SHA512_DIGEST_SIZE]);
 
 
+#define SHA256_HMAC_SIZE	(SHA256_DIGEST_SIZE)
+
+typedef struct {
+	SHA256_CTX sha256_ctx;
+	uint8_t key[SHA256_BLOCK_SIZE];
+} SHA256_HMAC_CTX;
+
+void sha256_hmac_init(SHA256_HMAC_CTX *ctx, const uint8_t *key, size_t keylen);
+void sha256_hmac_update(SHA256_HMAC_CTX *ctx, const uint8_t *data, size_t datalen);
+void sha256_hmac_finish(SHA256_HMAC_CTX *ctx, uint8_t mac[SHA256_HMAC_SIZE]);
+
+
 #ifdef __cplusplus
 }
 #endif

src/sha256_hmac.c

@@ -0,0 +1,74 @@
+/*
+ *  Copyright 2014-2026 The GmSSL Project. All Rights Reserved.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the License); you may
+ *  not use this file except in compliance with the License.
+ *
+ *  http://www.apache.org/licenses/LICENSE-2.0
+ */
+
+
+#include <string.h>
+#include <gmssl/sha2.h>
+#include <gmssl/error.h>
+
+/**
+ * HMAC_k(m) = H((k ^ opad) || H((k ^ ipad) || m))
+ * pseudo-code:
+ * function hmac(key, message)
+ *	opad = [0x5c * blocksize]
+ *	ipad = [0x36 * blocksize]
+ *	if (length(key) > blocksize) then
+ *		key = hash(key)
+ *	end if
+ *	for i from 0 to length(key) - 1 step 1
+ *		ipad[i] = ipad[i] XOR key[i]
+ *		opad[i] = opad[i] XOR key[i]
+ *	end for
+ *	return hash(opad || hash(ipad || message))
+ * end function
+ */
+
+
+#define IPAD	0x36
+#define OPAD	0x5C
+
+void sha256_hmac_init(SHA256_HMAC_CTX *ctx, const uint8_t *key, size_t key_len)
+{
+	int i;
+
+	if (key_len <= SHA256_BLOCK_SIZE) {
+		memcpy(ctx->key, key, key_len);
+		memset(ctx->key + key_len, 0, SHA256_BLOCK_SIZE - key_len);
+	} else {
+		sha256_init(&ctx->sha256_ctx);
+		sha256_update(&ctx->sha256_ctx, key, key_len);
+		sha256_finish(&ctx->sha256_ctx, ctx->key);
+		memset(ctx->key + SHA256_DIGEST_SIZE, 0,
+			SHA256_BLOCK_SIZE - SHA256_DIGEST_SIZE);
+	}
+	for (i = 0; i < SHA256_BLOCK_SIZE; i++) {
+		ctx->key[i] ^= IPAD;
+	}
+
+	sha256_init(&ctx->sha256_ctx);
+	sha256_update(&ctx->sha256_ctx, ctx->key, SHA256_BLOCK_SIZE);
+}
+
+void sha256_hmac_update(SHA256_HMAC_CTX *ctx, const uint8_t *data, size_t data_len)
+{
+	sha256_update(&ctx->sha256_ctx, data, data_len);
+}
+
+void sha256_hmac_finish(SHA256_HMAC_CTX *ctx, uint8_t mac[SHA256_HMAC_SIZE])
+{
+	int i;
+	for (i = 0; i < SHA256_BLOCK_SIZE; i++) {
+		ctx->key[i] ^= (IPAD ^ OPAD);
+	}
+	sha256_finish(&ctx->sha256_ctx, mac);
+	sha256_init(&ctx->sha256_ctx);
+	sha256_update(&ctx->sha256_ctx, ctx->key, SHA256_BLOCK_SIZE);
+	sha256_update(&ctx->sha256_ctx, mac, SHA256_DIGEST_SIZE);
+	sha256_finish(&ctx->sha256_ctx, mac);
+}