sha1dc: add collision-detecting sha1 implementation

This is pulled straight from:

  https://github.com/cr-marcstevens/sha1collisiondetection

with no modifications yet (though I've pulled in only the
subset of files necessary for Git to use).

This is commit 007905a93c973f55b2daed6585f9f6c23545bf66.

Further updates can be done like:

  git checkout -b vendor-sha1dc $this_commit
  cp /path/to/sha1dc/{LICENSE.txt,lib/*} sha1dc/
  git add -A sha1dc
  git commit -m "update sha1dc"

  git checkout -b update-sha1dc origin
  git merge vendor-sha1dc

Thanks to both Marc and Dan for making the code fit our
needs by doing both optimization work, cutting down on the
object size, and doing some syntactic changes to work better
with git. And to Linus for kicking off the "diet" work that
removed some of the unused code.

The license of the sha1dc code is the MIT license, which is
obviously compatible with the GPLv2 of git.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 105 insertions, 0 deletions

diff --git a/sha1dc/sha1.h b/sha1dc/sha1.h
new file mode 100644
index 0000000000..88556179b5
--- /dev/null
+++ b/sha1dc/sha1.h
@@ -0,0 +1,105 @@
+/***
+* Copyright 2017 Marc Stevens <marc@marc-stevens.nl>, Dan Shumow <danshu@microsoft.com>
+* Distributed under the MIT Software License.
+* See accompanying file LICENSE.txt or copy at
+* https://opensource.org/licenses/MIT
+***/
+
+#if defined(__cplusplus)
+extern "C" {
+#endif
+
+#include <stdint.h>
+
+/* uses SHA-1 message expansion to expand the first 16 words of W[] to 80 words */
+/* void sha1_message_expansion(uint32_t W[80]); */
+
+/* sha-1 compression function; first version takes a message block pre-parsed as 16 32-bit integers, second version takes an already expanded message) */
+/* void sha1_compression(uint32_t ihv[5], const uint32_t m[16]);
+void sha1_compression_W(uint32_t ihv[5], const uint32_t W[80]); */
+
+/* same as sha1_compression_W, but additionally store intermediate states */
+/* only stores states ii (the state between step ii-1 and step ii) when DOSTORESTATEii is defined in ubc_check.h */
+void sha1_compression_states(uint32_t[5], const uint32_t[16], uint32_t[80], uint32_t[80][5]);
+
+/*
+// function type for sha1_recompression_step_T (uint32_t ihvin[5], uint32_t ihvout[5], const uint32_t me2[80], const uint32_t state[5])
+// where 0 <= T < 80
+//       me2 is an expanded message (the expansion of an original message block XOR'ed with a disturbance vector's message block difference)
+//       state is the internal state (a,b,c,d,e) before step T of the SHA-1 compression function while processing the original message block
+// the function will return:
+//       ihvin: the reconstructed input chaining value
+//       ihvout: the reconstructed output chaining value
+*/
+typedef void(*sha1_recompression_type)(uint32_t*, uint32_t*, const uint32_t*, const uint32_t*);
+
+/* table of sha1_recompression_step_0, ... , sha1_recompression_step_79 */
+/* extern sha1_recompression_type sha1_recompression_step[80];*/
+
+/* a callback function type that can be set to be called when a collision block has been found: */
+/* void collision_block_callback(uint64_t byteoffset, const uint32_t ihvin1[5], const uint32_t ihvin2[5], const uint32_t m1[80], const uint32_t m2[80]) */
+typedef void(*collision_block_callback)(uint64_t, const uint32_t*, const uint32_t*, const uint32_t*, const uint32_t*);
+
+/* the SHA-1 context */
+typedef struct {
+	uint64_t total;
+	uint32_t ihv[5];
+	unsigned char buffer[64];
+	int found_collision;
+	int safe_hash;
+	int detect_coll;
+	int ubc_check;
+	int reduced_round_coll;
+	collision_block_callback callback;
+
+	uint32_t ihv1[5];
+	uint32_t ihv2[5];
+	uint32_t m1[80];
+	uint32_t m2[80];
+	uint32_t states[80][5];
+} SHA1_CTX;
+
+/* initialize SHA-1 context */
+void SHA1DCInit(SHA1_CTX*);
+
+/*
+// function to enable safe SHA-1 hashing:
+// collision attacks are thwarted by hashing a detected near-collision block 3 times
+// think of it as extending SHA-1 from 80-steps to 240-steps for such blocks:
+//   the best collision attacks against SHA-1 have complexity about 2^60,
+//   thus for 240-steps an immediate lower-bound for the best cryptanalytic attacks would 2^180
+//   an attacker would be better off using a generic birthday search of complexity 2^80
+//
+// enabling safe SHA-1 hashing will result in the correct SHA-1 hash for messages where no collision attack was detected
+// but it will result in a different SHA-1 hash for messages where a collision attack was detected
+// this will automatically invalidate SHA-1 based digital signature forgeries
+// enabled by default
+*/
+void SHA1DCSetSafeHash(SHA1_CTX*, int);
+
+/* function to disable or enable the use of Unavoidable Bitconditions (provides a significant speed up) */
+/* enabled by default */
+void SHA1DCSetUseUBC(SHA1_CTX*, int);
+
+/* function to disable or enable the use of Collision Detection */
+/* enabled by default */
+void SHA1DCSetUseDetectColl(SHA1_CTX*, int);
+
+/* function to disable or enable the detection of reduced-round SHA-1 collisions */
+/* disabled by default */
+void SHA1DCSetDetectReducedRoundCollision(SHA1_CTX*, int);
+
+/* function to set a callback function, pass NULL to disable */
+/* by default no callback set */
+void SHA1DCSetCallback(SHA1_CTX*, collision_block_callback);
+
+/* update SHA-1 context with buffer contents */
+void SHA1DCUpdate(SHA1_CTX*, const char*, size_t);
+
+/* obtain SHA-1 hash from SHA-1 context */
+/* returns: 0 = no collision detected, otherwise = collision found => warn user for active attack */
+int  SHA1DCFinal(unsigned char[20], SHA1_CTX*);
+
+#if defined(__cplusplus)
+}
+#endif