sshsh256.c

/*
 * SHA-256 algorithm as described at
 * 
 *   http://csrc.nist.gov/cryptval/shs.html
 */

#include "ssh.h"

/* ----------------------------------------------------------------------
 * Core SHA256 algorithm: processes 16-word blocks into a message digest.
 */

#define ror(x,y) ( ((x) << (32-y)) | (((uint32)(x)) >> (y)) )
#define shr(x,y) ( (((uint32)(x)) >> (y)) )
#define Ch(x,y,z) ( ((x) & (y)) ^ (~(x) & (z)) )
#define Maj(x,y,z) ( ((x) & (y)) ^ ((x) & (z)) ^ ((y) & (z)) )
#define bigsigma0(x) ( ror((x),2) ^ ror((x),13) ^ ror((x),22) )
#define bigsigma1(x) ( ror((x),6) ^ ror((x),11) ^ ror((x),25) )
#define smallsigma0(x) ( ror((x),7) ^ ror((x),18) ^ shr((x),3) )
#define smallsigma1(x) ( ror((x),17) ^ ror((x),19) ^ shr((x),10) )

void SHA256_Core_Init(SHA256_State *s) {
    s->h[0] = 0x6a09e667;
    s->h[1] = 0xbb67ae85;
    s->h[2] = 0x3c6ef372;
    s->h[3] = 0xa54ff53a;
    s->h[4] = 0x510e527f;
    s->h[5] = 0x9b05688c;
    s->h[6] = 0x1f83d9ab;
    s->h[7] = 0x5be0cd19;
}

void SHA256_Block(SHA256_State *s, uint32 *block) {
    uint32 w[80];
    uint32 a,b,c,d,e,f,g,h;
    static const int 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,
    };

    int t;

    for (t = 0; t < 16; t++)
        w[t] = block[t];

    for (t = 16; t < 64; t++)
	w[t] = smallsigma1(w[t-2]) + w[t-7] + smallsigma0(w[t-15]) + w[t-16];

    a = s->h[0]; b = s->h[1]; c = s->h[2]; d = s->h[3];
    e = s->h[4]; f = s->h[5]; g = s->h[6]; h = s->h[7];

    for (t = 0; t < 64; t+=8) {
        uint32 t1, t2;

#define ROUND(j,a,b,c,d,e,f,g,h) \
	t1 = h + bigsigma1(e) + Ch(e,f,g) + k[j] + w[j]; \
	t2 = bigsigma0(a) + Maj(a,b,c); \
        d = d + t1; h = t1 + t2;

	ROUND(t+0, a,b,c,d,e,f,g,h);
	ROUND(t+1, h,a,b,c,d,e,f,g);
	ROUND(t+2, g,h,a,b,c,d,e,f);
	ROUND(t+3, f,g,h,a,b,c,d,e);
	ROUND(t+4, e,f,g,h,a,b,c,d);
	ROUND(t+5, d,e,f,g,h,a,b,c);
	ROUND(t+6, c,d,e,f,g,h,a,b);
	ROUND(t+7, b,c,d,e,f,g,h,a);
    }

    s->h[0] += a; s->h[1] += b; s->h[2] += c; s->h[3] += d;
    s->h[4] += e; s->h[5] += f; s->h[6] += g; s->h[7] += h;
}

/* ----------------------------------------------------------------------
 * Outer SHA256 algorithm: take an arbitrary length byte string,
 * convert it into 16-word blocks with the prescribed padding at
 * the end, and pass those blocks to the core SHA256 algorithm.
 */

#define BLKSIZE 64

void SHA256_Init(SHA256_State *s) {
    SHA256_Core_Init(s);
    s->blkused = 0;
    s->lenhi = s->lenlo = 0;
}

void SHA256_Bytes(SHA256_State *s, const void *p, int len) {
    unsigned char *q = (unsigned char *)p;
    uint32 wordblock[16];
    uint32 lenw = len;
    int i;

    /*
     * Update the length field.
     */
    s->lenlo += lenw;
    s->lenhi += (s->lenlo < lenw);

    if (s->blkused && s->blkused+len < BLKSIZE) {
        /*
         * Trivial case: just add to the block.
         */
        memcpy(s->block + s->blkused, q, len);
        s->blkused += len;
    } else {
        /*
         * We must complete and process at least one block.
         */
        while (s->blkused + len >= BLKSIZE) {
            memcpy(s->block + s->blkused, q, BLKSIZE - s->blkused);
            q += BLKSIZE - s->blkused;
            len -= BLKSIZE - s->blkused;
            /* Now process the block. Gather bytes big-endian into words */
            for (i = 0; i < 16; i++) {
                wordblock[i] =
                    ( ((uint32)s->block[i*4+0]) << 24 ) |
                    ( ((uint32)s->block[i*4+1]) << 16 ) |
                    ( ((uint32)s->block[i*4+2]) <<  8 ) |
                    ( ((uint32)s->block[i*4+3]) <<  0 );
            }
            SHA256_Block(s, wordblock);
            s->blkused = 0;
        }
        memcpy(s->block, q, len);
        s->blkused = len;
    }
}

void SHA256_Final(SHA256_State *s, unsigned char *digest) {
    int i;
    int pad;
    unsigned char c[64];
    uint32 lenhi, lenlo;

    if (s->blkused >= 56)
        pad = 56 + 64 - s->blkused;
    else
        pad = 56 - s->blkused;

    lenhi = (s->lenhi << 3) | (s->lenlo >> (32-3));
    lenlo = (s->lenlo << 3);

    memset(c, 0, pad);
    c[0] = 0x80;
    SHA256_Bytes(s, &c, pad);

    c[0] = (lenhi >> 24) & 0xFF;
    c[1] = (lenhi >> 16) & 0xFF;
    c[2] = (lenhi >>  8) & 0xFF;
    c[3] = (lenhi >>  0) & 0xFF;
    c[4] = (lenlo >> 24) & 0xFF;
    c[5] = (lenlo >> 16) & 0xFF;
    c[6] = (lenlo >>  8) & 0xFF;
    c[7] = (lenlo >>  0) & 0xFF;

    SHA256_Bytes(s, &c, 8);

    for (i = 0; i < 8; i++) {
	digest[i*4+0] = (s->h[i] >> 24) & 0xFF;
	digest[i*4+1] = (s->h[i] >> 16) & 0xFF;
	digest[i*4+2] = (s->h[i] >>  8) & 0xFF;
	digest[i*4+3] = (s->h[i] >>  0) & 0xFF;
    }
}

void SHA256_Simple(const void *p, int len, unsigned char *output) {
    SHA256_State s;

    SHA256_Init(&s);
    SHA256_Bytes(&s, p, len);
    SHA256_Final(&s, output);
}

/*
 * Thin abstraction for things where hashes are pluggable.
 */

static void *sha256_init(void)
{
    SHA256_State *s;

    s = snew(SHA256_State);
    SHA256_Init(s);
    return s;
}

static void sha256_bytes(void *handle, void *p, int len)
{
    SHA256_State *s = handle;

    SHA256_Bytes(s, p, len);
}

static void sha256_final(void *handle, unsigned char *output)
{
    SHA256_State *s = handle;

    SHA256_Final(s, output);
    sfree(s);
}

const struct ssh_hash ssh_sha256 = {
    sha256_init, sha256_bytes, sha256_final, 32, "SHA-256"
};

/* ----------------------------------------------------------------------
 * The above is the SHA-256 algorithm itself. Now we implement the
 * HMAC wrapper on it.
 */

static void *sha256_make_context(void)
{
    return snewn(3, SHA256_State);
}

static void sha256_free_context(void *handle)
{
    sfree(handle);
}

static void sha256_key_internal(void *handle, unsigned char *key, int len)
{
    SHA256_State *keys = (SHA256_State *)handle;
    unsigned char foo[64];
    int i;

    memset(foo, 0x36, 64);
    for (i = 0; i < len && i < 64; i++)
	foo[i] ^= key[i];
    SHA256_Init(&keys[0]);
    SHA256_Bytes(&keys[0], foo, 64);

    memset(foo, 0x5C, 64);
    for (i = 0; i < len && i < 64; i++)
	foo[i] ^= key[i];
    SHA256_Init(&keys[1]);
    SHA256_Bytes(&keys[1], foo, 64);

    smemclr(foo, 64);		       /* burn the evidence */
}

static void sha256_key(void *handle, unsigned char *key)
{
    sha256_key_internal(handle, key, 32);
}

static void hmacsha256_start(void *handle)
{
    SHA256_State *keys = (SHA256_State *)handle;

    keys[2] = keys[0];		      /* structure copy */
}

static void hmacsha256_bytes(void *handle, unsigned char const *blk, int len)
{
    SHA256_State *keys = (SHA256_State *)handle;
    SHA256_Bytes(&keys[2], (void *)blk, len);
}

static void hmacsha256_genresult(void *handle, unsigned char *hmac)
{
    SHA256_State *keys = (SHA256_State *)handle;
    SHA256_State s;
    unsigned char intermediate[32];

    s = keys[2];		       /* structure copy */
    SHA256_Final(&s, intermediate);
    s = keys[1];		       /* structure copy */
    SHA256_Bytes(&s, intermediate, 32);
    SHA256_Final(&s, hmac);
}

static void sha256_do_hmac(void *handle, unsigned char *blk, int len,
			 unsigned long seq, unsigned char *hmac)
{
    unsigned char seqbuf[4];

    PUT_32BIT_MSB_FIRST(seqbuf, seq);
    hmacsha256_start(handle);
    hmacsha256_bytes(handle, seqbuf, 4);
    hmacsha256_bytes(handle, blk, len);
    hmacsha256_genresult(handle, hmac);
}

static void sha256_generate(void *handle, unsigned char *blk, int len,
			  unsigned long seq)
{
    sha256_do_hmac(handle, blk, len, seq, blk + len);
}

static int hmacsha256_verresult(void *handle, unsigned char const *hmac)
{
    unsigned char correct[32];
    hmacsha256_genresult(handle, correct);
    return !memcmp(correct, hmac, 32);
}

static int sha256_verify(void *handle, unsigned char *blk, int len,
		       unsigned long seq)
{
    unsigned char correct[32];
    sha256_do_hmac(handle, blk, len, seq, correct);
    return !memcmp(correct, blk + len, 32);
}

const struct ssh_mac ssh_hmac_sha256 = {
    sha256_make_context, sha256_free_context, sha256_key,
    sha256_generate, sha256_verify,
    hmacsha256_start, hmacsha256_bytes,
    hmacsha256_genresult, hmacsha256_verresult,
    "hmac-sha2-256",
    32,
    "HMAC-SHA-256"
};

#ifdef TEST

#include <stdio.h>
#include <stdlib.h>
#include <assert.h>

int main(void) {
    unsigned char digest[32];
    int i, j, errors;

    struct {
	const char *teststring;
	unsigned char digest[32];
    } tests[] = {
	{ "abc", {
	    0xba, 0x78, 0x16, 0xbf, 0x8f, 0x01, 0xcf, 0xea,
	    0x41, 0x41, 0x40, 0xde, 0x5d, 0xae, 0x22, 0x23,
	    0xb0, 0x03, 0x61, 0xa3, 0x96, 0x17, 0x7a, 0x9c,
	    0xb4, 0x10, 0xff, 0x61, 0xf2, 0x00, 0x15, 0xad,
	} },
	{ "abcdbcdecdefdefgefghfghighijhijkijkljklmklmnlmnomnopnopq", {
	    0x24, 0x8d, 0x6a, 0x61, 0xd2, 0x06, 0x38, 0xb8,
	    0xe5, 0xc0, 0x26, 0x93, 0x0c, 0x3e, 0x60, 0x39,
	    0xa3, 0x3c, 0xe4, 0x59, 0x64, 0xff, 0x21, 0x67,
	    0xf6, 0xec, 0xed, 0xd4, 0x19, 0xdb, 0x06, 0xc1,
	} },
    };

    errors = 0;

    for (i = 0; i < sizeof(tests) / sizeof(*tests); i++) {
	SHA256_Simple(tests[i].teststring,
		      strlen(tests[i].teststring), digest);
	for (j = 0; j < 32; j++) {
	    if (digest[j] != tests[i].digest[j]) {
		fprintf(stderr,
			"\"%s\" digest byte %d should be 0x%02x, is 0x%02x\n",
			tests[i].teststring, j, tests[i].digest[j], digest[j]);
		errors++;
	    }
	}
    }

    printf("%d errors\n", errors);

    return 0;
}

#endif