Started a SHA-256 implementation. Buggy so far.

.gitignore

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+*~

Makefile

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+test: test.o sha-256.o
+
+.PHONY: clean
+clean:
+	rm test *.o

sha-256.c

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+#include <stdint.h>
+#include <string.h>
+
+#include "sha-256.h"
+
+#define CHUNK_SIZE 64
+#define TOTAL_LEN_LEN 8
+
+/*
+ * Comments from pseudo-code at https://en.wikipedia.org/wiki/SHA-2 are reproduced here.
+ * When useful for clarification, portions of the pseudo-code are reproduced here too.
+ */
+
+/*
+ * Initialize array of round constants:
+ * (first 32 bits of the fractional parts of the cube roots of the first 64 primes 2..311):
+ */
+static const uint32_t k[] = {
+	0x428a2f98, 0x71374491, 0xb5c0fbcf, 0xe9b5dba5, 0x3956c25b, 0x59f111f1, 0x923f82a4, 0xab1c5ed5,
+	0xd807aa98, 0x12835b01, 0x243185be, 0x550c7dc3, 0x72be5d74, 0x80deb1fe, 0x9bdc06a7, 0xc19bf174,
+	0xe49b69c1, 0xefbe4786, 0x0fc19dc6, 0x240ca1cc, 0x2de92c6f, 0x4a7484aa, 0x5cb0a9dc, 0x76f988da,
+	0x983e5152, 0xa831c66d, 0xb00327c8, 0xbf597fc7, 0xc6e00bf3, 0xd5a79147, 0x06ca6351, 0x14292967,
+	0x27b70a85, 0x2e1b2138, 0x4d2c6dfc, 0x53380d13, 0x650a7354, 0x766a0abb, 0x81c2c92e, 0x92722c85,
+	0xa2bfe8a1, 0xa81a664b, 0xc24b8b70, 0xc76c51a3, 0xd192e819, 0xd6990624, 0xf40e3585, 0x106aa070,
+	0x19a4c116, 0x1e376c08, 0x2748774c, 0x34b0bcb5, 0x391c0cb3, 0x4ed8aa4a, 0x5b9cca4f, 0x682e6ff3,
+	0x748f82ee, 0x78a5636f, 0x84c87814, 0x8cc70208, 0x90befffa, 0xa4506ceb, 0xbef9a3f7, 0xc67178f2
+};
+
+struct buffer_state {
+	const uint8_t * p;
+	size_t len;
+	size_t total_len;
+	int single_one_delivered;
+	int total_len_delivered;
+};
+
+static inline uint32_t right_rot(uint32_t value, unsigned int count)
+{
+	/*
+	 * Defined behaviour in standard C for all count where 0 < count < 32,
+	 * which is what we need here.
+	 */
+	return value >> count | value << (32 - count);
+}
+
+static void init_buf_state(struct buffer_state * state, const void * input, size_t len)
+{
+	state->p = input;
+	state->len = len;
+	state->total_len = len;
+	state->single_one_delivered = 0;
+	state->total_len_delivered = 0;
+}
+
+static int calc_chunk(uint8_t chunk[CHUNK_SIZE], struct buffer_state * state)
+{
+	size_t space_in_chunk;
+
+	if (state->total_len_delivered) {
+		return 0;
+	}
+
+	if (state->len >= CHUNK_SIZE) {
+		memcpy(chunk, state->p, CHUNK_SIZE);
+		state->p += CHUNK_SIZE;
+		state->len -= CHUNK_SIZE;
+		return 1;
+
+	}
+
+	memcpy(chunk, state->p, state->len);
+	chunk += state->len;
+	space_in_chunk = CHUNK_SIZE - state->len;
+
+	/* If we are here, space_in_chunk is one at minimum. */
+	if (!state->single_one_delivered) {
+		*chunk++ = 0x80;
+		space_in_chunk -= 1;
+		state->single_one_delivered = 1;
+	}
+
+	/*
+	 * Now:
+	 * - either there is enough space left for the total length, and we can conclude,
+	 * - or there is too little space left, and we have to pad the rest of this chunk with zeroes.
+	 * In the latter case, we will conclude at the next pass.
+	 */
+	if (space_in_chunk >= TOTAL_LEN_LEN) {
+		const size_t left = space_in_chunk - TOTAL_LEN_LEN;
+		const size_t len = state->total_len;
+		memset(chunk, 0x00, left);
+		chunk += left;
+
+		chunk[0] = (uint8_t) (len >> 56);
+		chunk[1] = (uint8_t) (len >> 48);
+		chunk[2] = (uint8_t) (len >> 40);
+		chunk[3] = (uint8_t) (len >> 32);
+		chunk[4] = (uint8_t) (len >> 24);
+		chunk[5] = (uint8_t) (len >> 16);
+		chunk[6] = (uint8_t) (len >> 8);
+		chunk[7] = (uint8_t) len;
+
+		state->total_len_delivered = 1;
+	} else {
+		memset(chunk, 0x00, space_in_chunk);
+	}
+
+	return 1;
+}
+
+void calc_sha_256(uint8_t hash[32], const void * input, size_t len)
+{
+	/*
+	 * Note 1: All variables are 32 bit unsigned integers and addition is calculated modulo 232
+	 * Note 2: For each round, there is one round constant k[i] and one entry in the message schedule array w[i], 0 = i = 63
+	 * Note 3: The compression function uses 8 working variables, a through h
+	 * Note 4: Big-endian convention is used when expressing the constants in this pseudocode,
+	 *     and when parsing message block data from bytes to words, for example,
+	 *     the first word of the input message "abc" after padding is 0x61626380
+	 */
+
+	/*
+	 * Initialize hash values:
+	 * (first 32 bits of the fractional parts of the square roots of the first 8 primes 2..19):
+	 */
+
+	uint32_t h0 = 0x6a09e667;
+	uint32_t h1 = 0xbb67ae85;
+	uint32_t h2 = 0x3c6ef372;
+	uint32_t h3 = 0xa54ff53a;
+	uint32_t h4 = 0x510e527f;
+	uint32_t h5 = 0x9b05688c;
+	uint32_t h6 = 0x1f83d9ab;
+	uint32_t h7 = 0x5be0cd19;
+
+	/* 512-bit chunks is what we will operate on. */
+
+	uint8_t chunk[64];
+
+	struct buffer_state state;
+
+	init_buf_state(&state, input, len);
+
+	while (calc_chunk(chunk, &state)) {
+		uint32_t a, b, c, d, e, f, g, h;
+		
+		/*
+		 * create a 64-entry message schedule array w[0..63] of 32-bit words
+		 * (The initial values in w[0..63] don't matter, so many implementations zero them here)
+		 * copy chunk into first 16 words w[0..15] of the message schedule array
+		 */
+		uint32_t w[64];
+		const uint8_t *p = chunk;
+
+		memset(w, 0x00, sizeof w);
+		for (int i = 0; i < 16; i++) {
+			w[i] = (uint32_t) p[0] << 24 | (uint32_t) p[1] << 16 |
+				(uint32_t) p[2] << 8 | (uint32_t) p[3];
+			p += 4;
+		}
+
+		/* Extend the first 16 words into the remaining 48 words w[16..63] of the message schedule array: */
+		for (int i = 16; i < 64; i++) {
+			const uint32_t s0 = right_rot(w[i - 15], 7) ^ right_rot(w[i - 15], 18) ^ w[i - 15] >> 3;
+			const uint32_t s1 = right_rot(w[i - 2], 17) ^ right_rot(w[i - 2], 19) ^ w[i - 2] >> 10;
+			w[i] = w[i - 16] + s0 + w[i - 7] + s1;
+		}
+		
+		/* Initialize working variables to current hash value: */
+		a = h0;
+		b = h1;
+		c = h2;
+		d = h3;
+		e = h4;
+		f = h5;
+		g = h6;
+		h = h7;
+
+		/* Compression function main loop: */
+		for (int i = 0; i < 64; i++) {
+			const uint32_t s1 = right_rot(e, 6) ^ right_rot(e, 11) ^ right_rot(e, 25);
+			const uint32_t ch = e & f ^ ~e & g;
+			const uint32_t temp1 = h + s1 + ch + k[i] + w[i];
+			const uint32_t s0 = right_rot(a, 2) ^right_rot(a, 13) ^ right_rot(a, 22);
+			const uint32_t maj = a & b ^ a & c ^ b & c;
+			const uint32_t temp2 = s0 + maj;
+
+			h = g;
+			g = f;
+			f = e;
+			e = d + temp1;
+			d = c;
+			c = b;
+			b = a;
+			a = temp1 + temp2;
+		}
+
+		/* Add the compressed chunk to the current hash value: */
+		h0 = h0 + a;
+		h1 = h1 + b;
+		h2 = h2 + c;
+		h3 = h3 + d;
+		h4 = h4 + e;
+		h5 = h5 + f;
+		h6 = h6 + g;
+		h7 = h7 + h;
+	}
+
+	hash[0] = (uint8_t) (h0 >> 24);
+	hash[1] = (uint8_t) (h0 >> 16);
+	hash[2] = (uint8_t) (h0 >> 8);
+	hash[3] = (uint8_t) h0;
+	hash[4] = (uint8_t) (h1 >> 24);
+	hash[5] = (uint8_t) (h1 >> 16);
+	hash[6] = (uint8_t) (h1 >> 8);
+	hash[7] = (uint8_t) h1;
+	hash[8] = (uint8_t) (h2 >> 24);
+	hash[9] = (uint8_t) (h2 >> 16);
+	hash[10] = (uint8_t) (h2 >> 8);
+	hash[11] = (uint8_t) h2;
+	hash[12] = (uint8_t) (h3 >> 24);
+	hash[13] = (uint8_t) (h3 >> 16);
+	hash[14] = (uint8_t) (h3 >> 8);
+	hash[15] = (uint8_t) h3;
+	hash[16] = (uint8_t) (h4 >> 24);
+	hash[17] = (uint8_t) (h4 >> 16);
+	hash[18] = (uint8_t) (h4 >> 8);
+	hash[19] = (uint8_t) h4;
+	hash[20] = (uint8_t) (h5 >> 24);
+	hash[21] = (uint8_t) (h5 >> 16);
+	hash[22] = (uint8_t) (h5 >> 8);
+	hash[23] = (uint8_t) h5;
+	hash[24] = (uint8_t) (h6 >> 24);
+	hash[25] = (uint8_t) (h6 >> 16);
+	hash[26] = (uint8_t) (h6 >> 8);
+	hash[27] = (uint8_t) h6;
+	hash[28] = (uint8_t) (h7 >> 24);
+	hash[29] = (uint8_t) (h7 >> 16);
+	hash[30] = (uint8_t) (h7 >> 8);
+	hash[31] = (uint8_t) h7;
+}

sha-256.h

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+void calc_sha_256(uint8_t hash[32], const void * input, size_t len);

test.c

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+#include <stdint.h>
+#include <stdio.h>
+
+#include "sha-256.h"
+
+int main()
+{
+	uint8_t hash[32];
+	calc_sha_256(hash, "hello\n", 6);
+	for (size_t i = 0; i < sizeof hash; i++) {
+		printf("%02x", hash[i]);
+	}
+	printf("\n");
+}

tmp.txt

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+hello