1 files changed, 41 insertions, 0 deletions
diff --git a/src/hmac.c b/src/hmac.c
new file mode 100644
index 0000000..5175ee2
--- /dev/null
+++ b/src/hmac.c
@@ -0,0 +1,41 @@
+#include <string.h>
+
+#include "sha1.h"
+
+#define IPAD (0x36)
+#define OPAD (0x5C)
+
+void
+hmac_sha1(uint8_t *restrict out,
+          const uint8_t *restrict key, size_t keysz,
+          const uint8_t *restrict msg, size_t msgsz)
+{
+	uint8_t keyext[SHA1BLKSZ] = {0},
+	        keyipad[SHA1BLKSZ],
+			keyopad[SHA1BLKSZ];
+
+	if (keysz > SHA1BLKSZ) {
+		sha1_t sha;
+		sha1init(&sha);
+		sha1hash(&sha, key, keysz);
+		sha1end(&sha, keyext);
+	} else
+		memcpy(keyext, key, keysz);
+
+	for (size_t i = 0; i < sizeof(keyext); i++) {
+		keyipad[i] = keyext[i] ^ IPAD;
+		keyopad[i] = keyext[i] ^ OPAD;
+	}
+
+	sha1_t sha;
+	uint8_t dgst[SHA1DGSTSZ];
+	sha1init(&sha);
+	sha1hash(&sha, keyipad, sizeof(keyipad));
+	sha1hash(&sha, msg, msgsz);
+	sha1end(&sha, dgst);
+
+	sha1init(&sha);
+	sha1hash(&sha, keyopad, sizeof(keyopad));
+	sha1hash(&sha, dgst, sizeof(dgst));
+	sha1end(&sha, out);
+}