1 files changed, 45 insertions, 0 deletions
diff --git a/hmac_init.c b/hmac_init.c
new file mode 100644
index 0000000..4aee2c2
--- /dev/null
+++ b/hmac_init.c
@@ -0,0 +1,45 @@
+/* See LICENSE file for copyright and license details. */
+#include "common.h"
+
+
+/**
+ * Initialise an HMAC state
+ * 
+ * @param   state        The state that should be initialised
+ * @param   algorithm    The hashing algorithm
+ * @param   key          The key
+ * @param   key_length   The length of key, in bits
+ * @return               Zero on success, -1 on error
+ */
+int
+libsha2_hmac_init(struct libsha2_hmac_state *restrict state, enum libsha2_algorithm algorithm,
+                  const void *restrict key_, size_t keylen)
+{
+	const unsigned char *restrict key = key_;
+	size_t i;
+
+	state->sha2_state.algorithm = algorithm;
+	state->outsize = libsha2_algorithm_output_size(algorithm) * 8;
+	state->inited = 0;
+
+	if (keylen <= state->sha2_state.chunk_size * 8) {
+		memset(state->ipad, 0x36, sizeof(state->ipad));
+		memset(state->opad, 0x5C, sizeof(state->opad));
+		for (i = 0, keylen /= 8; i < keylen; i++) {
+			state->ipad[i] ^= key[i];
+			state->opad[i] ^= key[i];
+		}
+	} else {
+		memset(state->ipad, 0, sizeof(state->ipad));
+		if (libsha2_init(&state->sha2_state, algorithm))
+			return -1;
+		libsha2_digest(&state->sha2_state, key, keylen, state->ipad);
+		memcpy(state->opad, state->ipad, sizeof(state->ipad));
+		for (i = 0; i < sizeof(state->ipad); i++) {
+			state->ipad[i] ^= 0x36;
+			state->opad[i] ^= 0x5C;
+		}
+	}
+
+	return 0;
+}