Added RSA/OAEP implementation.

[BearSSL] / src / rsa / rsa_oaep_pad.c

diff --git a/src/rsa/rsa_oaep_pad.c b/src/rsa/rsa_oaep_pad.c
new file mode 100644 (file)
index 0000000..5327dc2
--- /dev/null
+++ b/src/rsa/rsa_oaep_pad.c
@@ -0,0 +1,112 @@
+/*
+ * 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"
+
+/*
+ * Hash some data. This is put as a separate function so that stack
+ * allocation of the hash function context is done only for the duration
+ * of the hash.
+ */
+static void
+hash_data(const br_hash_class *dig, void *dst, const void *src, size_t len)
+{
+       br_hash_compat_context hc;
+
+       hc.vtable = dig;
+       dig->init(&hc.vtable);
+       dig->update(&hc.vtable, src, len);
+       dig->out(&hc.vtable, dst);
+}
+
+/* see inner.h */
+size_t
+br_rsa_oaep_pad(const br_prng_class **rnd, const br_hash_class *dig,
+       const void *label, size_t label_len,
+       const br_rsa_public_key *pk,
+       void *dst, size_t dst_max_len,
+       const void *src, size_t src_len)
+{
+       size_t k, hlen;
+       unsigned char *buf;
+
+       hlen = br_digest_size(dig);
+
+       /*
+        * Compute actual modulus length (in bytes).
+        */
+       k = pk->nlen;
+       while (k > 0 && pk->n[k - 1] == 0) {
+               k --;
+       }
+
+       /*
+        * An error is reported if:
+        *  - the modulus is too short;
+        *  - the source message length is too long;
+        *  - the destination buffer is too short.
+        */
+       if (k < ((hlen << 1) + 2)
+               || src_len > (k - (hlen << 1) - 2)
+               || dst_max_len < k)
+       {
+               return 0;
+       }
+
+       /*
+        * Apply padding. At this point, things cannot fail.
+        */
+       buf = dst;
+
+       /*
+        * Assemble: DB = lHash || PS || 0x01 || M
+        * We first place the source message M with memmove(), so that
+        * overlaps between source and destination buffers are supported.
+        */
+       memmove(buf + k - src_len, src, src_len);
+       hash_data(dig, buf + 1 + hlen, label, label_len);
+       memset(buf + 1 + (hlen << 1), 0, k - src_len - (hlen << 1) - 2);
+       buf[k - src_len - 1] = 0x01;
+
+       /*
+        * Make the random seed.
+        */
+       (*rnd)->generate(rnd, buf + 1, hlen);
+
+       /*
+        * Mask DB with the mask generated from the seed.
+        */
+       br_mgf1_xor(buf + 1 + hlen, k - hlen - 1, dig, buf + 1, hlen);
+
+       /*
+        * Mask the seed with the mask generated from the masked DB.
+        */
+       br_mgf1_xor(buf + 1, hlen, dig, buf + 1 + hlen, k - hlen - 1);
+
+       /*
+        * Padding result: EM = 0x00 || maskedSeed || maskedDB.
+        */
+       buf[0] = 0x00;
+       return k;
+}