Initial import.

src/ssl/ssl_rec_gcm.c

@@ -0,0 +1,235 @@
+/*
+ * Copyright (c) 2016 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"
+
+/*
+ * GCM initialisation. This does everything except setting the vtable,
+ * which depends on whether this is a context for encrypting or for
+ * decrypting.
+ */
+static void
+gen_gcm_init(br_sslrec_gcm_context *cc,
+	const br_block_ctr_class *bc_impl,
+	const void *key, size_t key_len,
+	br_ghash gh_impl,
+	const void *iv)
+{
+	unsigned char tmp[12];
+
+	cc->seq = 0;
+	bc_impl->init(&cc->bc.vtable, key, key_len);
+	cc->gh = gh_impl;
+	memcpy(cc->iv, iv, sizeof cc->iv);
+	memset(cc->h, 0, sizeof cc->h);
+	memset(tmp, 0, sizeof tmp);
+	bc_impl->run(&cc->bc.vtable, tmp, 0, cc->h, sizeof cc->h);
+}
+
+static void
+in_gcm_init(br_sslrec_gcm_context *cc,
+	const br_block_ctr_class *bc_impl,
+	const void *key, size_t key_len,
+	br_ghash gh_impl,
+	const void *iv)
+{
+	cc->vtable.in = &br_sslrec_in_gcm_vtable;
+	gen_gcm_init(cc, bc_impl, key, key_len, gh_impl, iv);
+}
+
+static int
+gcm_check_length(const br_sslrec_gcm_context *cc, size_t rlen)
+{
+	/*
+	 * GCM adds a fixed overhead:
+	 *   8 bytes for the nonce_explicit (before the ciphertext)
+	 *  16 bytes for the authentication tag (after the ciphertext)
+	 */
+	(void)cc;
+	return rlen >= 24 && rlen <= (16384 + rlen);
+}
+
+/*
+ * Compute the authentication tag. The value written in 'tag' must still
+ * be CTR-encrypted.
+ */
+static void
+do_tag(br_sslrec_gcm_context *cc,
+	int record_type, unsigned version,
+	void *data, size_t len, void *tag)
+{
+	unsigned char header[13];
+	unsigned char footer[16];
+
+	/*
+	 * Compute authentication tag. Three elements must be injected in
+	 * sequence, each possibly 0-padded to reach a length multiple
+	 * of the block size: the 13-byte header (sequence number, record
+	 * type, protocol version, record length), the cipher text, and
+	 * the word containing the encodings of the bit lengths of the two
+	 * other elements.
+	 */
+	br_enc64be(header, cc->seq ++);
+	header[8] = (unsigned char)record_type;
+	br_enc16be(header + 9, version);
+	br_enc16be(header + 11, len);
+	br_enc64be(footer, (uint64_t)(sizeof header) << 3);
+	br_enc64be(footer + 8, (uint64_t)len << 3);
+	memset(tag, 0, 16);
+	cc->gh(tag, cc->h, header, sizeof header);
+	cc->gh(tag, cc->h, data, len);
+	cc->gh(tag, cc->h, footer, sizeof footer);
+}
+
+/*
+ * Do CTR encryption. This also does CTR encryption of a single block at
+ * address 'xortag' with the counter value appropriate for the final
+ * processing of the authentication tag.
+ */
+static void
+do_ctr(br_sslrec_gcm_context *cc, const void *nonce, void *data, size_t len,
+	void *xortag)
+{
+	unsigned char iv[12];
+
+	memcpy(iv, cc->iv, 4);
+	memcpy(iv + 4, nonce, 8);
+	cc->bc.vtable->run(&cc->bc.vtable, iv, 2, data, len);
+	cc->bc.vtable->run(&cc->bc.vtable, iv, 1, xortag, 16);
+}
+
+static unsigned char *
+gcm_decrypt(br_sslrec_gcm_context *cc,
+	int record_type, unsigned version, void *data, size_t *data_len)
+{
+	unsigned char *buf;
+	size_t len, u;
+	uint32_t bad;
+	unsigned char tag[16];
+
+	buf = (unsigned char *)data + 8;
+	len = *data_len - 24;
+	do_tag(cc, record_type, version, buf, len, tag);
+	do_ctr(cc, data, buf, len, tag);
+
+	/*
+	 * Compare the computed tag with the value from the record. It
+	 * is possibly useless to do a constant-time comparison here,
+	 * but it does not hurt.
+	 */
+	bad = 0;
+	for (u = 0; u < 16; u ++) {
+		bad |= tag[u] ^ buf[len + u];
+	}
+	if (bad) {
+		return NULL;
+	}
+	*data_len = len;
+	return buf;
+}
+
+/* see bearssl_ssl.h */
+const br_sslrec_in_gcm_class br_sslrec_in_gcm_vtable = {
+	{
+		sizeof(br_sslrec_gcm_context),
+		(int (*)(const br_sslrec_in_class *const *, size_t))
+			&gcm_check_length,
+		(unsigned char *(*)(const br_sslrec_in_class **,
+			int, unsigned, void *, size_t *))
+			&gcm_decrypt
+	},
+	(void (*)(const br_sslrec_in_gcm_class **,
+		const br_block_ctr_class *, const void *, size_t,
+		br_ghash, const void *))
+		&in_gcm_init
+};
+
+static void
+out_gcm_init(br_sslrec_gcm_context *cc,
+	const br_block_ctr_class *bc_impl,
+	const void *key, size_t key_len,
+	br_ghash gh_impl,
+	const void *iv)
+{
+	cc->vtable.out = &br_sslrec_out_gcm_vtable;
+	gen_gcm_init(cc, bc_impl, key, key_len, gh_impl, iv);
+}
+
+static void
+gcm_max_plaintext(const br_sslrec_gcm_context *cc,
+	size_t *start, size_t *end)
+{
+	size_t len;
+
+	(void)cc;
+	*start += 8;
+	len = *end - *start - 16;
+	if (len > 16384) {
+		len = 16384;
+	}
+	*end = *start + len;
+}
+
+static unsigned char *
+gcm_encrypt(br_sslrec_gcm_context *cc,
+	int record_type, unsigned version, void *data, size_t *data_len)
+{
+	unsigned char *buf;
+	size_t u, len;
+	unsigned char tmp[16];
+
+	buf = (unsigned char *)data;
+	len = *data_len;
+	memset(tmp, 0, sizeof tmp);
+	br_enc64be(buf - 8, cc->seq);
+	do_ctr(cc, buf - 8, buf, len, tmp);
+	do_tag(cc, record_type, version, buf, len, buf + len);
+	for (u = 0; u < 16; u ++) {
+		buf[len + u] ^= tmp[u];
+	}
+	len += 24;
+	buf -= 13;
+	buf[0] = (unsigned char)record_type;
+	br_enc16be(buf + 1, version);
+	br_enc16be(buf + 3, len);
+	*data_len = len + 5;
+	return buf;
+}
+
+/* see bearssl_ssl.h */
+const br_sslrec_out_gcm_class br_sslrec_out_gcm_vtable = {
+	{
+		sizeof(br_sslrec_gcm_context),
+		(void (*)(const br_sslrec_out_class *const *,
+			size_t *, size_t *))
+			&gcm_max_plaintext,
+		(unsigned char *(*)(const br_sslrec_out_class **,
+			int, unsigned, void *, size_t *))
+			&gcm_encrypt
+	},
+	(void (*)(const br_sslrec_out_gcm_class **,
+		const br_block_ctr_class *, const void *, size_t,
+		br_ghash, const void *))
+		&out_gcm_init
+};