1 files changed, 525 insertions, 0 deletions
diff --git a/third_party/bearssl/src/eax.c b/third_party/bearssl/src/eax.c
new file mode 100644
index 0000000..bcc704a
--- /dev/null
+++ b/third_party/bearssl/src/eax.c
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+/*
+ * Copyright (c) 2017 Thomas Pornin <[email protected]>
+ *
+ * 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"
+
+/*
+ * Implementation Notes
+ * ====================
+ *
+ * The combined CTR + CBC-MAC functions can only handle full blocks,
+ * so some buffering is necessary. Moreover, EAX has a special padding
+ * rule for CBC-MAC, which implies that we cannot compute the MAC over
+ * the last received full block until we know whether we are at the
+ * end of the data or not.
+ *
+ *  - 'ptr' contains a value from 1 to 16, which is the number of bytes
+ *    accumulated in buf[] that still needs to be processed with the
+ *    current OMAC computation. Beware that this can go to 16: a
+ *    complete block cannot be processed until it is known whether it
+ *    is the last block or not. However, it can never be 0, because
+ *    OMAC^t works on an input that is at least one-block long.
+ *
+ *  - When processing the message itself, CTR encryption/decryption is
+ *    also done at the same time. The first 'ptr' bytes of buf[] then
+ *    contains the encrypted bytes, while the last '16 - ptr' bytes of
+ *    buf[] are the remnants of the stream block, to be used against
+ *    the next input bytes, when available.
+ *
+ *  - The current counter and running CBC-MAC values are kept in 'ctr'
+ *    and 'cbcmac', respectively.
+ *
+ *  - The derived keys for padding are kept in L2 and L4 (double and
+ *    quadruple of Enc_K(0^n), in GF(2^128), respectively).
+ */
+
+/*
+ * Start an OMAC computation; the first block is the big-endian
+ * representation of the provided value ('val' must fit on one byte).
+ * We make it a delayed block because it may also be the last one,
+ */
+static void
+omac_start(br_eax_context *ctx, unsigned val)
+{
+	memset(ctx->cbcmac, 0, sizeof ctx->cbcmac);
+	memset(ctx->buf, 0, sizeof ctx->buf);
+	ctx->buf[15] = val;
+	ctx->ptr = 16;
+}
+
+/*
+ * Double a value in finite field GF(2^128), defined with modulus
+ * X^128+X^7+X^2+X+1.
+ */
+static void
+double_gf128(unsigned char *dst, const unsigned char *src)
+{
+	unsigned cc;
+	int i;
+
+	cc = 0x87 & -((unsigned)src[0] >> 7);
+	for (i = 15; i >= 0; i --) {
+		unsigned z;
+
+		z = (src[i] << 1) ^ cc;
+		cc = z >> 8;
+		dst[i] = (unsigned char)z;
+	}
+}
+
+/*
+ * Apply padding to the last block, currently in ctx->buf (with
+ * ctx->ptr bytes), and finalize OMAC computation.
+ */
+static void
+do_pad(br_eax_context *ctx)
+{
+	unsigned char *pad;
+	size_t ptr, u;
+
+	ptr = ctx->ptr;
+	if (ptr == 16) {
+		pad = ctx->L2;
+	} else {
+		ctx->buf[ptr ++] = 0x80;
+		memset(ctx->buf + ptr, 0x00, 16 - ptr);
+		pad = ctx->L4;
+	}
+	for (u = 0; u < sizeof ctx->buf; u ++) {
+		ctx->buf[u] ^= pad[u];
+	}
+	(*ctx->bctx)->mac(ctx->bctx, ctx->cbcmac, ctx->buf, sizeof ctx->buf);
+}
+
+/*
+ * Apply CBC-MAC on the provided data, with buffering management.
+ *
+ * Upon entry, two situations are acceptable:
+ *
+ *   ctx->ptr == 0: there is no data to process in ctx->buf
+ *   ctx->ptr == 16: there is a full block of unprocessed data in ctx->buf
+ *
+ * Upon exit, ctx->ptr may be zero only if it was already zero on entry,
+ * and len == 0. In all other situations, ctx->ptr will be non-zero on
+ * exit (and may have value 16).
+ */
+static void
+do_cbcmac_chunk(br_eax_context *ctx, const void *data, size_t len)
+{
+	size_t ptr;
+
+	if (len == 0) {
+		return;
+	}
+	ptr = len & (size_t)15;
+	if (ptr == 0) {
+		len -= 16;
+		ptr = 16;
+	} else {
+		len -= ptr;
+	}
+	if (ctx->ptr == 16) {
+		(*ctx->bctx)->mac(ctx->bctx, ctx->cbcmac,
+			ctx->buf, sizeof ctx->buf);
+	}
+	(*ctx->bctx)->mac(ctx->bctx, ctx->cbcmac, data, len);
+	memcpy(ctx->buf, (const unsigned char *)data + len, ptr);
+	ctx->ptr = ptr;
+}
+
+/* see bearssl_aead.h */
+void
+br_eax_init(br_eax_context *ctx, const br_block_ctrcbc_class **bctx)
+{
+	unsigned char tmp[16], iv[16];
+
+	ctx->vtable = &br_eax_vtable;
+	ctx->bctx = bctx;
+
+	/*
+	 * Encrypt a whole-zero block to compute L2 and L4.
+	 */
+	memset(tmp, 0, sizeof tmp);
+	memset(iv, 0, sizeof iv);
+	(*bctx)->ctr(bctx, iv, tmp, sizeof tmp);
+	double_gf128(ctx->L2, tmp);
+	double_gf128(ctx->L4, ctx->L2);
+}
+
+/* see bearssl_aead.h */
+void
+br_eax_capture(const br_eax_context *ctx, br_eax_state *st)
+{
+	/*
+	 * We capture the three OMAC* states _after_ processing the
+	 * initial block (assuming that nonce, message and AAD are
+	 * all non-empty).
+	 */
+	int i;
+
+	memset(st->st, 0, sizeof st->st);
+	for (i = 0; i < 3; i ++) {
+		unsigned char tmp[16];
+
+		memset(tmp, 0, sizeof tmp);
+		tmp[15] = (unsigned char)i;
+		(*ctx->bctx)->mac(ctx->bctx, st->st[i], tmp, sizeof tmp);
+	}
+}
+
+/* see bearssl_aead.h */
+void
+br_eax_reset(br_eax_context *ctx, const void *nonce, size_t len)
+{
+	/*
+	 * Process nonce with OMAC^0.
+	 */
+	omac_start(ctx, 0);
+	do_cbcmac_chunk(ctx, nonce, len);
+	do_pad(ctx);
+	memcpy(ctx->nonce, ctx->cbcmac, sizeof ctx->cbcmac);
+
+	/*
+	 * Start OMAC^1 for the AAD ("header" in the EAX specification).
+	 */
+	omac_start(ctx, 1);
+
+	/*
+	 * We use ctx->head[0] as temporary flag to mark that we are
+	 * using a "normal" reset().
+	 */
+	ctx->head[0] = 0;
+}
+
+/* see bearssl_aead.h */
+void
+br_eax_reset_pre_aad(br_eax_context *ctx, const br_eax_state *st,
+	const void *nonce, size_t len)
+{
+	if (len == 0) {
+		omac_start(ctx, 0);
+	} else {
+		memcpy(ctx->cbcmac, st->st[0], sizeof ctx->cbcmac);
+		ctx->ptr = 0;
+		do_cbcmac_chunk(ctx, nonce, len);
+	}
+	do_pad(ctx);
+	memcpy(ctx->nonce, ctx->cbcmac, sizeof ctx->cbcmac);
+
+	memcpy(ctx->cbcmac, st->st[1], sizeof ctx->cbcmac);
+	ctx->ptr = 0;
+
+	memcpy(ctx->ctr, st->st[2], sizeof ctx->ctr);
+
+	/*
+	 * We use ctx->head[0] as a flag to indicate that we use a
+	 * a recorded state, with ctx->ctr containing the preprocessed
+	 * first block for OMAC^2.
+	 */
+	ctx->head[0] = 1;
+}
+
+/* see bearssl_aead.h */
+void
+br_eax_reset_post_aad(br_eax_context *ctx, const br_eax_state *st,
+	const void *nonce, size_t len)
+{
+	if (len == 0) {
+		omac_start(ctx, 0);
+	} else {
+		memcpy(ctx->cbcmac, st->st[0], sizeof ctx->cbcmac);
+		ctx->ptr = 0;
+		do_cbcmac_chunk(ctx, nonce, len);
+	}
+	do_pad(ctx);
+	memcpy(ctx->nonce, ctx->cbcmac, sizeof ctx->cbcmac);
+	memcpy(ctx->ctr, ctx->nonce, sizeof ctx->nonce);
+
+	memcpy(ctx->head, st->st[1], sizeof ctx->head);
+
+	memcpy(ctx->cbcmac, st->st[2], sizeof ctx->cbcmac);
+	ctx->ptr = 0;
+}
+
+/* see bearssl_aead.h */
+void
+br_eax_aad_inject(br_eax_context *ctx, const void *data, size_t len)
+{
+	size_t ptr;
+
+	ptr = ctx->ptr;
+
+	/*
+	 * If there is a partial block, first complete it.
+	 */
+	if (ptr < 16) {
+		size_t clen;
+
+		clen = 16 - ptr;
+		if (len <= clen) {
+			memcpy(ctx->buf + ptr, data, len);
+			ctx->ptr = ptr + len;
+			return;
+		}
+		memcpy(ctx->buf + ptr, data, clen);
+		data = (const unsigned char *)data + clen;
+		len -= clen;
+	}
+
+	/*
+	 * We now have a full block in buf[], and this is not the last
+	 * block.
+	 */
+	do_cbcmac_chunk(ctx, data, len);
+}
+
+/* see bearssl_aead.h */
+void
+br_eax_flip(br_eax_context *ctx)
+{
+	int from_capture;
+
+	/*
+	 * ctx->head[0] may be non-zero if the context was reset with
+	 * a pre-AAD captured state. In that case, ctx->ctr[] contains
+	 * the state for OMAC^2 _after_ processing the first block.
+	 */
+	from_capture = ctx->head[0];
+
+	/*
+	 * Complete the OMAC computation on the AAD.
+	 */
+	do_pad(ctx);
+	memcpy(ctx->head, ctx->cbcmac, sizeof ctx->cbcmac);
+
+	/*
+	 * Start OMAC^2 for the encrypted data.
+	 * If the context was initialized from a captured state, then
+	 * the OMAC^2 value is in the ctr[] array.
+	 */
+	if (from_capture) {
+		memcpy(ctx->cbcmac, ctx->ctr, sizeof ctx->cbcmac);
+		ctx->ptr = 0;
+	} else {
+		omac_start(ctx, 2);
+	}
+
+	/*
+	 * Initial counter value for CTR is the processed nonce.
+	 */
+	memcpy(ctx->ctr, ctx->nonce, sizeof ctx->nonce);
+}
+
+/* see bearssl_aead.h */
+void
+br_eax_run(br_eax_context *ctx, int encrypt, void *data, size_t len)
+{
+	unsigned char *dbuf;
+	size_t ptr;
+
+	/*
+	 * Ensure that there is actual data to process.
+	 */
+	if (len == 0) {
+		return;
+	}
+
+	dbuf = data;
+	ptr = ctx->ptr;
+
+	/*
+	 * We may have ptr == 0 here if we initialized from a captured
+	 * state. In that case, there is no partially consumed block
+	 * or unprocessed data.
+	 */
+	if (ptr != 0 && ptr != 16) {
+		/*
+		 * We have a partially consumed block.
+		 */
+		size_t u, clen;
+
+		clen = 16 - ptr;
+		if (len <= clen) {
+			clen = len;
+		}
+		if (encrypt) {
+			for (u = 0; u < clen; u ++) {
+				ctx->buf[ptr + u] ^= dbuf[u];
+			}
+			memcpy(dbuf, ctx->buf + ptr, clen);
+		} else {
+			for (u = 0; u < clen; u ++) {
+				unsigned dx, sx;
+
+				sx = ctx->buf[ptr + u];
+				dx = dbuf[u];
+				ctx->buf[ptr + u] = dx;
+				dbuf[u] = sx ^ dx;
+			}
+		}
+
+		if (len <= clen) {
+			ctx->ptr = ptr + clen;
+			return;
+		}
+		dbuf += clen;
+		len -= clen;
+	}
+
+	/*
+	 * We now have a complete encrypted block in buf[] that must still
+	 * be processed with OMAC, and this is not the final buf.
+	 * Exception: when ptr == 0, no block has been produced yet.
+	 */
+	if (ptr != 0) {
+		(*ctx->bctx)->mac(ctx->bctx, ctx->cbcmac,
+			ctx->buf, sizeof ctx->buf);
+	}
+
+	/*
+	 * Do CTR encryption or decryption and CBC-MAC for all full blocks
+	 * except the last.
+	 */
+	ptr = len & (size_t)15;
+	if (ptr == 0) {
+		len -= 16;
+		ptr = 16;
+	} else {
+		len -= ptr;
+	}
+	if (encrypt) {
+		(*ctx->bctx)->encrypt(ctx->bctx, ctx->ctr, ctx->cbcmac,
+			dbuf, len);
+	} else {
+		(*ctx->bctx)->decrypt(ctx->bctx, ctx->ctr, ctx->cbcmac,
+			dbuf, len);
+	}
+	dbuf += len;
+
+	/*
+	 * Compute next block of CTR stream, and use it to finish
+	 * encrypting or decrypting the data.
+	 */
+	memset(ctx->buf, 0, sizeof ctx->buf);
+	(*ctx->bctx)->ctr(ctx->bctx, ctx->ctr, ctx->buf, sizeof ctx->buf);
+	if (encrypt) {
+		size_t u;
+
+		for (u = 0; u < ptr; u ++) {
+			ctx->buf[u] ^= dbuf[u];
+		}
+		memcpy(dbuf, ctx->buf, ptr);
+	} else {
+		size_t u;
+
+		for (u = 0; u < ptr; u ++) {
+			unsigned dx, sx;
+
+			sx = ctx->buf[u];
+			dx = dbuf[u];
+			ctx->buf[u] = dx;
+			dbuf[u] = sx ^ dx;
+		}
+	}
+	ctx->ptr = ptr;
+}
+
+/*
+ * Complete tag computation. The final tag is written in ctx->cbcmac.
+ */
+static void
+do_final(br_eax_context *ctx)
+{
+	size_t u;
+
+	do_pad(ctx);
+
+	/*
+	 * Authentication tag is the XOR of the three OMAC outputs for
+	 * the nonce, AAD and encrypted data.
+	 */
+	for (u = 0; u < 16; u ++) {
+		ctx->cbcmac[u] ^= ctx->nonce[u] ^ ctx->head[u];
+	}
+}
+
+/* see bearssl_aead.h */
+void
+br_eax_get_tag(br_eax_context *ctx, void *tag)
+{
+	do_final(ctx);
+	memcpy(tag, ctx->cbcmac, sizeof ctx->cbcmac);
+}
+
+/* see bearssl_aead.h */
+void
+br_eax_get_tag_trunc(br_eax_context *ctx, void *tag, size_t len)
+{
+	do_final(ctx);
+	memcpy(tag, ctx->cbcmac, len);
+}
+
+/* see bearssl_aead.h */
+uint32_t
+br_eax_check_tag_trunc(br_eax_context *ctx, const void *tag, size_t len)
+{
+	unsigned char tmp[16];
+	size_t u;
+	int x;
+
+	br_eax_get_tag(ctx, tmp);
+	x = 0;
+	for (u = 0; u < len; u ++) {
+		x |= tmp[u] ^ ((const unsigned char *)tag)[u];
+	}
+	return EQ0(x);
+}
+
+/* see bearssl_aead.h */
+uint32_t
+br_eax_check_tag(br_eax_context *ctx, const void *tag)
+{
+	return br_eax_check_tag_trunc(ctx, tag, 16);
+}
+
+/* see bearssl_aead.h */
+const br_aead_class br_eax_vtable = {
+	16,
+	(void (*)(const br_aead_class **, const void *, size_t))
+		&br_eax_reset,
+	(void (*)(const br_aead_class **, const void *, size_t))
+		&br_eax_aad_inject,
+	(void (*)(const br_aead_class **))
+		&br_eax_flip,
+	(void (*)(const br_aead_class **, int, void *, size_t))
+		&br_eax_run,
+	(void (*)(const br_aead_class **, void *))
+		&br_eax_get_tag,
+	(uint32_t (*)(const br_aead_class **, const void *))
+		&br_eax_check_tag,
+	(void (*)(const br_aead_class **, void *, size_t))
+		&br_eax_get_tag_trunc,
+	(uint32_t (*)(const br_aead_class **, const void *, size_t))
+		&br_eax_check_tag_trunc
+};