From 7286cb832ad48977790ccdb0cee063a5d05d5d75 Mon Sep 17 00:00:00 2001
From: Vincent Hanquez <vincent@snarc.org>
Date: Tue, 14 Feb 2017 17:51:40 +0000
Subject: [PATCH] Add better constants for trampoline buffer

---
 cbits/cryptonite_sha3.c |  5 +++--
 cbits/cryptonite_sha3.h | 16 ++++++++++++++++
 2 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/cbits/cryptonite_sha3.c b/cbits/cryptonite_sha3.c
index c9df6fb..e942fe6 100755
--- a/cbits/cryptonite_sha3.c
+++ b/cbits/cryptonite_sha3.c
@@ -104,7 +104,8 @@ static inline void sha3_do_chunk(uint64_t state[25], uint64_t buf[], int bufsz)
  */
 void cryptonite_sha3_init(struct sha3_ctx *ctx, uint32_t hashlen)
 {
-	int bufsz = 200 - 2 * (hashlen / 8);
+	/* assert(hashlen >= SHA3_BITSIZE_MIN && hashlen <= SHA3_BITSIZE_MAX) */
+	int bufsz = SHA3_BUF_SIZE(hashlen);
 	memset(ctx, 0, sizeof(*ctx) + bufsz);
 	ctx->bufsz = bufsz;
 }
@@ -131,7 +132,7 @@ void cryptonite_sha3_update(struct sha3_ctx *ctx, const uint8_t *data, uint32_t
 	}
 
 	if (need_alignment(data, 8)) {
-		uint64_t tramp[200 - 2 * (128 / 8)];
+		uint64_t tramp[SHA3_BUF_SIZE_MAX/8];
 		ASSERT_ALIGNMENT(tramp, 8);
 		for (; len >= ctx->bufsz; len -= ctx->bufsz, data += ctx->bufsz) {
 			memcpy(tramp, data, ctx->bufsz / 8);
diff --git a/cbits/cryptonite_sha3.h b/cbits/cryptonite_sha3.h
index 233f1e1..ca4e6f9 100755
--- a/cbits/cryptonite_sha3.h
+++ b/cbits/cryptonite_sha3.h
@@ -35,6 +35,22 @@ struct sha3_ctx
 };
 
 #define SHA3_CTX_SIZE		sizeof(struct sha3_ctx)
+#define SHA3_CTX_BUF_MAX_SIZE   (SHA3_CTX_SIZE + SHA3_BUF_SIZE_MAX)
+#define SHA3_BITSIZE_MIN   	128
+#define SHA3_BITSIZE_MAX    	512
+
+#define SHA3_BUF_SIZE(bitsize)  (200 - 2 * ((bitsize) / 8))
+
+#define SHA3_BUF_SIZE_MIN       SHA3_BUF_SIZE(SHA3_BITSIZE_MAX)
+#define SHA3_BUF_SIZE_MAX       SHA3_BUF_SIZE(SHA3_BITSIZE_MIN)
+
+/*
+ * buffer size:
+ *
+ * 128 bits (shake 128 bits) => 200 - 2 * (128 / 8) = 200 - 2*16 = 200 - 32  = 168 bytes
+ * 224 bits (SHA3 224 bits)  => 200 - 2 * (224 / 8) = 200 - 2*28 = 200 - 56  = 144 bytes
+ * 512 bits (SHA3 512 bits)  => 200 - 2 * (512 / 8) = 200 - 2*64 = 200 - 128 = 72 bytes
+ */
 
 void cryptonite_sha3_init(struct sha3_ctx *ctx, uint32_t hashlen);
 void cryptonite_sha3_update(struct sha3_ctx *ctx, const uint8_t *data, uint32_t len);