putty/sshsha.c

/*
 * SHA1 hash algorithm. Used in SSH2 as a MAC, and the transform is
 * also used as a `stirring' function for the PuTTY random number
 * pool. Implemented directly from the specification by Simon
 * Tatham.
 */

#include "ssh.h"

typedef unsigned int uint32;

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

#define rol(x,y) ( ((x) << (y)) | (((uint32)x) >> (32-y)) )

void SHA_Core_Init(uint32 h[5]) {
    h[0] = 0x67452301;
    h[1] = 0xefcdab89;
    h[2] = 0x98badcfe;
    h[3] = 0x10325476;
    h[4] = 0xc3d2e1f0;
}

void SHATransform(word32 *digest, word32 *block) {
    word32 w[80];
    word32 a,b,c,d,e;
    int t;

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

    for (t = 16; t < 80; t++) {
        word32 tmp = w[t-3] ^ w[t-8] ^ w[t-14] ^ w[t-16];
        w[t] = rol(tmp, 1);
    }

    a = digest[0];
    b = digest[1];
    c = digest[2];
    d = digest[3];
    e = digest[4];

    for (t = 0; t < 20; t++) {
        word32 tmp = rol(a, 5) + ( (b&c) | (d&~b) ) + e + w[t] + 0x5a827999;
        e = d; d = c; c = rol(b, 30); b = a; a = tmp;
    }
    for (t = 20; t < 40; t++) {
        word32 tmp = rol(a, 5) + (b^c^d) + e + w[t] + 0x6ed9eba1;
        e = d; d = c; c = rol(b, 30); b = a; a = tmp;
    }
    for (t = 40; t < 60; t++) {
        word32 tmp = rol(a, 5) + ( (b&c) | (b&d) | (c&d) ) + e + w[t] + 0x8f1bbcdc;
        e = d; d = c; c = rol(b, 30); b = a; a = tmp;
    }
    for (t = 60; t < 80; t++) {
        word32 tmp = rol(a, 5) + (b^c^d) + e + w[t] + 0xca62c1d6;
        e = d; d = c; c = rol(b, 30); b = a; a = tmp;
    }

    digest[0] += a;
    digest[1] += b;
    digest[2] += c;
    digest[3] += d;
    digest[4] += e;
}

/* ----------------------------------------------------------------------
 * Outer SHA 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 SHA algorithm.
 */

void SHA_Init(SHA_State *s) {
    SHA_Core_Init(s->h);
    s->blkused = 0;
    s->lenhi = s->lenlo = 0;
}

void SHA_Bytes(SHA_State *s, 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 < 64) {
        /*
         * 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 >= 64) {
            memcpy(s->block + s->blkused, q, 64 - s->blkused);
            q += 64 - s->blkused;
            len -= 64 - 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 );
            }
            SHATransform(s->h, wordblock);
            s->blkused = 0;
        }
        memcpy(s->block, q, len);
        s->blkused = len;
    }
}

void SHA_Final(SHA_State *s, unsigned char *output) {
    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;
    SHA_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;

    SHA_Bytes(s, &c, 8);

    for (i = 0; i < 5; i++) {
        output[i*4  ] = (s->h[i] >> 24) & 0xFF;
        output[i*4+1] = (s->h[i] >> 16) & 0xFF;
        output[i*4+2] = (s->h[i] >>  8) & 0xFF;
        output[i*4+3] = (s->h[i]      ) & 0xFF;
    }
}

void SHA_Simple(void *p, int len, unsigned char *output) {
    SHA_State s;

    SHA_Init(&s);
    SHA_Bytes(&s, p, len);
    SHA_Final(&s, output);
}

/* ----------------------------------------------------------------------
 * The above is the SHA-1 algorithm itself. Now we implement the
 * HMAC wrapper on it.
 */

static SHA_State sha1_cs_mac_s1, sha1_cs_mac_s2;
static SHA_State sha1_sc_mac_s1, sha1_sc_mac_s2;

static void sha1_key(SHA_State *s1, SHA_State *s2,
                     unsigned char *key, int len) {
    unsigned char foo[64];
    int i;

    memset(foo, 0x36, 64);
    for (i = 0; i < len && i < 64; i++)
        foo[i] ^= key[i];
    SHA_Init(s1);
    SHA_Bytes(s1, foo, 64);

    memset(foo, 0x5C, 64);
    for (i = 0; i < len && i < 64; i++)
        foo[i] ^= key[i];
    SHA_Init(s2);
    SHA_Bytes(s2, foo, 64);

    memset(foo, 0, 64);                /* burn the evidence */
}

static void sha1_cskey(unsigned char *key) {
    sha1_key(&sha1_cs_mac_s1, &sha1_cs_mac_s2, key, 20);
}

static void sha1_sckey(unsigned char *key) {
    sha1_key(&sha1_sc_mac_s1, &sha1_sc_mac_s2, key, 20);
}

static void sha1_do_hmac(SHA_State *s1, SHA_State *s2,
                         unsigned char *blk, int len, unsigned long seq,
                         unsigned char *hmac) {
    SHA_State s;
    unsigned char intermediate[20];

    intermediate[0] = (unsigned char)((seq >> 24) & 0xFF);
    intermediate[1] = (unsigned char)((seq >> 16) & 0xFF);
    intermediate[2] = (unsigned char)((seq >>  8) & 0xFF);
    intermediate[3] = (unsigned char)((seq      ) & 0xFF);

    s = *s1;                           /* structure copy */
    SHA_Bytes(&s, intermediate, 4);
    SHA_Bytes(&s, blk, len);
    SHA_Final(&s, intermediate);
    s = *s2;                           /* structure copy */
    SHA_Bytes(&s, intermediate, 20);
    SHA_Final(&s, hmac);
}

static void sha1_generate(unsigned char *blk, int len, unsigned long seq) {
    sha1_do_hmac(&sha1_cs_mac_s1, &sha1_cs_mac_s2, blk, len, seq, blk+len);
}

static int sha1_verify(unsigned char *blk, int len, unsigned long seq) {
    unsigned char correct[20];
    sha1_do_hmac(&sha1_sc_mac_s1, &sha1_sc_mac_s2, blk, len, seq, correct);
    return !memcmp(correct, blk+len, 20);
}

struct ssh_mac ssh_sha1 = {
    sha1_cskey, sha1_sckey,
    sha1_generate,
    sha1_verify,
    "hmac-sha1",
    20
};