Added generic HKDF implementation.

src/kdf/hkdf.c

@@ -0,0 +1,107 @@
+/*
+ * Copyright (c) 2018 Thomas Pornin <pornin@bolet.org>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining 
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be 
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, 
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND 
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
+ * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+ * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+#include "inner.h"
+
+const unsigned char br_hkdf_no_salt = 0;
+
+/* see bearssl_kdf.h */
+void
+br_hkdf_init(br_hkdf_context *hc, const br_hash_class *digest_vtable,
+	const void *salt, size_t salt_len)
+{
+	br_hmac_key_context kc;
+	unsigned char tmp[64];
+
+	if (salt == BR_HKDF_NO_SALT) {
+		salt = tmp;
+		salt_len = br_digest_size(digest_vtable);
+		memset(tmp, 0, salt_len);
+	}
+	br_hmac_key_init(&kc, digest_vtable, salt, salt_len);
+	br_hmac_init(&hc->u.hmac_ctx, &kc, 0);
+	hc->dig_len = br_hmac_size(&hc->u.hmac_ctx);
+}
+
+/* see bearssl_kdf.h */
+void
+br_hkdf_inject(br_hkdf_context *hc, const void *ikm, size_t ikm_len)
+{
+	br_hmac_update(&hc->u.hmac_ctx, ikm, ikm_len);
+}
+
+/* see bearssl_kdf.h */
+void
+br_hkdf_flip(br_hkdf_context *hc)
+{
+	unsigned char tmp[64];
+
+	br_hmac_out(&hc->u.hmac_ctx, tmp);
+	br_hmac_key_init(&hc->u.prk_ctx,
+		br_hmac_get_digest(&hc->u.hmac_ctx), tmp, hc->dig_len);
+	hc->ptr = hc->dig_len;
+	hc->chunk_num = 0;
+}
+
+/* see bearssl_kdf.h */
+size_t
+br_hkdf_produce(br_hkdf_context *hc,
+	const void *info, size_t info_len, void *out, size_t out_len)
+{
+	size_t tlen;
+
+	tlen = 0;
+	while (out_len > 0) {
+		size_t clen;
+
+		if (hc->ptr == hc->dig_len) {
+			br_hmac_context hmac_ctx;
+			unsigned char x;
+
+			hc->chunk_num ++;
+			if (hc->chunk_num == 256) {
+				return tlen;
+			}
+			x = hc->chunk_num;
+			br_hmac_init(&hmac_ctx, &hc->u.prk_ctx, 0);
+			if (x != 1) {
+				br_hmac_update(&hmac_ctx, hc->buf, hc->dig_len);
+			}
+			br_hmac_update(&hmac_ctx, info, info_len);
+			br_hmac_update(&hmac_ctx, &x, 1);
+			br_hmac_out(&hmac_ctx, hc->buf);
+			hc->ptr = 0;
+		}
+		clen = hc->dig_len - hc->ptr;
+		if (clen > out_len) {
+			clen = out_len;
+		}
+		memcpy(out, hc->buf + hc->ptr, clen);
+		out = (unsigned char *)out + clen;
+		out_len -= clen;
+		hc->ptr += clen;
+		tlen += clen;
+	}
+	return tlen;
+}