src/hash/sha1dc/sha1.h

/***
* 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
***/

#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 ihv[5], const uint32_t W[80], uint32_t states[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 bigendian;
	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* ctx, int detect_coll);

// 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*, unsigned);

// 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*);