1 files changed, 80 insertions, 0 deletions

diff --git a/cbits/cryptonite_xsalsa.c b/cbits/cryptonite_xsalsa.c
new file mode 100644
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+++ b/cbits/cryptonite_xsalsa.c
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+/*
+ * Copyright (c) 2016 Brandon Hamilton <brandon.hamilton@gmail.com>
+ * 
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of the author nor the names of his contributors
+ *    may be used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+#include <stdint.h>
+#include <string.h>
+#include "cryptonite_xsalsa.h"
+#include "cryptonite_bitfn.h"
+
+static inline uint32_t load32(const uint8_t *p)
+{
+  return le32_to_cpu(*((uint32_t *) p));
+}
+
+/* XSalsa20 algorithm as described in https://cr.yp.to/snuffle/xsalsa-20081128.pdf */
+void cryptonite_xsalsa_init(cryptonite_salsa_context *ctx, uint8_t nb_rounds,
+                            uint32_t keylen, const uint8_t *key,
+                            uint32_t ivlen, const uint8_t *iv)
+{
+  memset(ctx, 0, sizeof(*ctx));
+  ctx->nb_rounds = nb_rounds;
+
+  /* Create initial 512-bit input block:
+       (x0, x5, x10, x15) is the Salsa20 constant
+       (x1, x2, x3, x4, x11, x12, x13, x14) is a 256-bit key
+       (x6, x7, x8, x9) is the first 128 bits of a 192-bit nonce
+  */
+  cryptonite_salsa_init_core(&ctx->st, keylen, key, 8, iv);
+  ctx->st.d[ 8] = load32(iv + 8);
+  ctx->st.d[ 9] = load32(iv + 12);
+
+  /* Compute (z0, z1, . . . , z15) = doubleround ^(r/2) (x0, x1, . . . , x15) */
+  block hSalsa;
+  memset(&hSalsa, 0, sizeof(block));
+  cryptonite_salsa_core_xor(nb_rounds, &hSalsa, &ctx->st);
+ 
+  /* Build a new 512-bit input block (x′0, x′1, . . . , x′15):
+       (x′0, x′5, x′10, x′15) is the Salsa20 constant
+       (x′1,x′2,x′3,x′4,x′11,x′12,x′13,x′14) = (z0,z5,z10,z15,z6,z7,z8,z9)
+       (x′6,x′7) is the last 64 bits of the 192-bit nonce
+       (x′8, x′9) is a 64-bit block counter.
+  */
+  ctx->st.d[ 1] = hSalsa.d[ 0] - ctx->st.d[ 0];
+  ctx->st.d[ 2] = hSalsa.d[ 5] - ctx->st.d[ 5];
+  ctx->st.d[ 3] = hSalsa.d[10] - ctx->st.d[10];
+  ctx->st.d[ 4] = hSalsa.d[15] - ctx->st.d[15];
+  ctx->st.d[11] = hSalsa.d[ 6] - ctx->st.d[ 6];
+  ctx->st.d[12] = hSalsa.d[ 7] - ctx->st.d[ 7];
+  ctx->st.d[13] = hSalsa.d[ 8] - ctx->st.d[ 8];
+  ctx->st.d[14] = hSalsa.d[ 9] - ctx->st.d[ 9];
+  ctx->st.d[ 6] = load32(iv + 16);
+  ctx->st.d[ 7] = load32(iv + 20);
+  ctx->st.d[ 8] = 0;
+  ctx->st.d[ 9] = 0;
+}
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