sshrsa.c

大名鼎鼎的远程登录软件putty的Symbian版源码

/*
 * RSA implementation for PuTTY.
 */

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

#include "ssh.h"
#include "misc.h"

#define GET_32BIT(cp) \
    (((unsigned long)(unsigned char)(cp)[0] << 24) | \
    ((unsigned long)(unsigned char)(cp)[1] << 16) | \
    ((unsigned long)(unsigned char)(cp)[2] << 8) | \
    ((unsigned long)(unsigned char)(cp)[3]))

#define PUT_32BIT(cp, value) { \
    (cp)[0] = (unsigned char)((value) >> 24); \
    (cp)[1] = (unsigned char)((value) >> 16); \
    (cp)[2] = (unsigned char)((value) >> 8); \
    (cp)[3] = (unsigned char)(value); }

int makekey(unsigned char *data, int len, struct RSAKey *result,
	    unsigned char **keystr, int order)
{
    unsigned char *p = data;
    int i, n;

    if (len < 4)
	return -1;

    if (result) {
	result->bits = 0;
	for (i = 0; i < 4; i++)
	    result->bits = (result->bits << 8) + *p++;
    } else
	p += 4;

    len -= 4;

    /*
     * order=0 means exponent then modulus (the keys sent by the
     * server). order=1 means modulus then exponent (the keys
     * stored in a keyfile).
     */

    if (order == 0) {
	n = ssh1_read_bignum(p, len, result ? &result->exponent : NULL);
	if (n < 0) return -1;
	p += n;
	len -= n;
    }

    n = ssh1_read_bignum(p, len, result ? &result->modulus : NULL);
    if (n < 0 || (result && bignum_bitcount(result->modulus) == 0)) return -1;
    if (result)
	result->bytes = n - 2;
    if (keystr)
	*keystr = p + 2;
    p += n;
    len -= n;

    if (order == 1) {
	n = ssh1_read_bignum(p, len, result ? &result->exponent : NULL);
	if (n < 0) return -1;
	p += n;
	len -= n;
    }
    return p - data;
}

int makeprivate(unsigned char *data, int len, struct RSAKey *result)
{
    return ssh1_read_bignum(data, len, &result->private_exponent);
}

int rsaencrypt(unsigned char *data, int length, struct RSAKey *key)
{
    Bignum b1, b2;
    int i;
    unsigned char *p;

    if (key->bytes < length + 4)
	return 0;		       /* RSA key too short! */

    memmove(data + key->bytes - length, data, length);
    data[0] = 0;
    data[1] = 2;

    for (i = 2; i < key->bytes - length - 1; i++) {
	do {
	    data[i] = random_byte();
	} while (data[i] == 0);
    }
    data[key->bytes - length - 1] = 0;

    b1 = bignum_from_bytes(data, key->bytes);

    b2 = modpow(b1, key->exponent, key->modulus);

    p = data;
    for (i = key->bytes; i--;) {
	*p++ = bignum_byte(b2, i);
    }

    freebn(b1);
    freebn(b2);

    return 1;
}

static void sha512_mpint(SHA512_State * s, Bignum b)
{
    unsigned char lenbuf[4];
    int len;
    len = (bignum_bitcount(b) + 8) / 8;
    PUT_32BIT(lenbuf, len);
    SHA512_Bytes(s, lenbuf, 4);
    while (len-- > 0) {
	lenbuf[0] = bignum_byte(b, len);
	SHA512_Bytes(s, lenbuf, 1);
    }
    memset(lenbuf, 0, sizeof(lenbuf));
}

/*
 * This function is a wrapper on modpow(). It has the same effect
 * as modpow(), but employs RSA blinding to protect against timing
 * attacks.
 */
static Bignum rsa_privkey_op(Bignum input, struct RSAKey *key)
{
    Bignum random, random_encrypted, random_inverse;
    Bignum input_blinded, ret_blinded;
    Bignum ret;

    SHA512_State ss;
    unsigned char digest512[64];
    int digestused = lenof(digest512);
    int hashseq = 0;

    /*
     * Start by inventing a random number chosen uniformly from the
     * range 2..modulus-1. (We do this by preparing a random number
     * of the right length and retrying if it's greater than the
     * modulus, to prevent any potential Bleichenbacher-like
     * attacks making use of the uneven distribution within the
     * range that would arise from just reducing our number mod n.
     * There are timing implications to the potential retries, of
     * course, but all they tell you is the modulus, which you
     * already knew.)
     * 
     * To preserve determinism and avoid Pageant needing to share
     * the random number pool, we actually generate this `random'
     * number by hashing stuff with the private key.
     */
    while (1) {
	int bits, byte, bitsleft, v;
	random = copybn(key->modulus);
	/*
	 * Find the topmost set bit. (This function will return its
	 * index plus one.) Then we'll set all bits from that one
	 * downwards randomly.
	 */
	bits = bignum_bitcount(random);
	byte = 0;
	bitsleft = 0;
	while (bits--) {
	    if (bitsleft <= 0) {
		bitsleft = 8;
		/*
		 * Conceptually the following few lines are equivalent to
		 *    byte = random_byte();
		 */
		if (digestused >= lenof(digest512)) {
		    unsigned char seqbuf[4];
		    PUT_32BIT(seqbuf, hashseq);
		    SHA512_Init(&ss);
		    SHA512_Bytes(&ss, "RSA deterministic blinding", 26);
		    SHA512_Bytes(&ss, seqbuf, sizeof(seqbuf));
		    sha512_mpint(&ss, key->private_exponent);
		    SHA512_Final(&ss, digest512);
		    hashseq++;

		    /*
		     * Now hash that digest plus the signature
		     * input.
		     */
		    SHA512_Init(&ss);
		    SHA512_Bytes(&ss, digest512, sizeof(digest512));
		    sha512_mpint(&ss, input);
		    SHA512_Final(&ss, digest512);

		    digestused = 0;
		}
		byte = digest512[digestused++];
	    }
	    v = byte & 1;
	    byte >>= 1;
	    bitsleft--;
	    bignum_set_bit(random, bits, v);
	}

	/*
	 * Now check that this number is strictly greater than
	 * zero, and strictly less than modulus.
	 */
	if (bignum_cmp(random, Zero) <= 0 ||
	    bignum_cmp(random, key->modulus) >= 0) {
	    freebn(random);
	    continue;
	} else {
	    break;
	}
    }

    /*
     * RSA blinding relies on the fact that (xy)^d mod n is equal
     * to (x^d mod n) * (y^d mod n) mod n. We invent a random pair
     * y and y^d; then we multiply x by y, raise to the power d mod
     * n as usual, and divide by y^d to recover x^d. Thus an
     * attacker can't correlate the timing of the modpow with the
     * input, because they don't know anything about the number
     * that was input to the actual modpow.
     * 
     * The clever bit is that we don't have to do a huge modpow to
     * get y and y^d; we will use the number we just invented as
     * _y^d_, and use the _public_ exponent to compute (y^d)^e = y
     * from it, which is much faster to do.
     */
    random_encrypted = modpow(random, key->exponent, key->modulus);
    random_inverse = modinv(random, key->modulus);
    input_blinded = modmul(input, random_encrypted, key->modulus);
    ret_blinded = modpow(input_blinded, key->private_exponent, key->modulus);
    ret = modmul(ret_blinded, random_inverse, key->modulus);

    freebn(ret_blinded);
    freebn(input_blinded);
    freebn(random_inverse);
    freebn(random_encrypted);
    freebn(random);

    return ret;
}

Bignum rsadecrypt(Bignum input, struct RSAKey *key)
{
    return rsa_privkey_op(input, key);
}

int rsastr_len(struct RSAKey *key)
{
    Bignum md, ex;
    int mdlen, exlen;

    md = key->modulus;
    ex = key->exponent;
    mdlen = (bignum_bitcount(md) + 15) / 16;
    exlen = (bignum_bitcount(ex) + 15) / 16;
    return 4 * (mdlen + exlen) + 20;
}

void rsastr_fmt(char *str, struct RSAKey *key)
{
    Bignum md, ex;
    int len = 0, i, nibbles;
    static const char hex[] = "0123456789abcdef";

    md = key->modulus;
    ex = key->exponent;

    len += sprintf(str + len, "0x");

    nibbles = (3 + bignum_bitcount(ex)) / 4;
    if (nibbles < 1)
	nibbles = 1;
    for (i = nibbles; i--;)
	str[len++] = hex[(bignum_byte(ex, i / 2) >> (4 * (i % 2))) & 0xF];

    len += sprintf(str + len, ",0x");

    nibbles = (3 + bignum_bitcount(md)) / 4;
    if (nibbles < 1)
	nibbles = 1;
    for (i = nibbles; i--;)
	str[len++] = hex[(bignum_byte(md, i / 2) >> (4 * (i % 2))) & 0xF];

    str[len] = '\0';
}

/*
 * Generate a fingerprint string for the key. Compatible with the
 * OpenSSH fingerprint code.
 */
void rsa_fingerprint(char *str, int len, struct RSAKey *key)
{
    struct MD5Context md5c;
    unsigned char digest[16];
    char buffer[16 * 3 + 40];
    int numlen, slen, i;

    MD5Init(&md5c);
    numlen = ssh1_bignum_length(key->modulus) - 2;
    for (i = numlen; i--;) {
	unsigned char c = bignum_byte(key->modulus, i);
	MD5Update(&md5c, &c, 1);
    }
    numlen = ssh1_bignum_length(key->exponent) - 2;
    for (i = numlen; i--;) {
	unsigned char c = bignum_byte(key->exponent, i);
	MD5Update(&md5c, &c, 1);
    }
    MD5Final(digest, &md5c);

    sprintf(buffer, "%d ", bignum_bitcount(key->modulus));
    for (i = 0; i < 16; i++)
	sprintf(buffer + strlen(buffer), "%s%02x", i ? ":" : "",
		digest[i]);
    strncpy(str, buffer, len);
    str[len - 1] = '\0';
    slen = strlen(str);
    if (key->comment && slen < len - 1) {
	str[slen] = ' ';
	strncpy(str + slen + 1, key->comment, len - slen - 1);
	str[len - 1] = '\0';
    }
}

/*
 * Verify that the public data in an RSA key matches the private
 * data. We also check the private data itself: we ensure that p >
 * q and that iqmp really is the inverse of q mod p.
 */
int rsa_verify(struct RSAKey *key)
{
    Bignum n, ed, pm1, qm1;
    int cmp;

    /* n must equal pq. */
    n = bigmul(key->p, key->q);
    cmp = bignum_cmp(n, key->modulus);
    freebn(n);
    if (cmp != 0)
	return 0;

    /* e * d must be congruent to 1, modulo (p-1) and modulo (q-1). */
    pm1 = copybn(key->p);
    decbn(pm1);
    ed = modmul(key->exponent, key->private_exponent, pm1);
    cmp = bignum_cmp(ed, One);
    sfree(ed);
    if (cmp != 0)
	return 0;

    qm1 = copybn(key->q);
    decbn(qm1);
    ed = modmul(key->exponent, key->private_exponent, qm1);
    cmp = bignum_cmp(ed, One);
    sfree(ed);
    if (cmp != 0)
	return 0;

    /*
     * Ensure p > q.
     */
    if (bignum_cmp(key->p, key->q) <= 0)
	return 0;

    /*
     * Ensure iqmp * q is congruent to 1, modulo p.
     */
    n = modmul(key->iqmp, key->q, key->p);
    cmp = bignum_cmp(n, One);
    sfree(n);
    if (cmp != 0)
	return 0;

    return 1;
}

/* Public key blob as used by Pageant: exponent before modulus. */
unsigned char *rsa_public_blob(struct RSAKey *key, int *len)
{
    int length, pos;
    unsigned char *ret;

    length = (ssh1_bignum_length(key->modulus) +
	      ssh1_bignum_length(key->exponent) + 4);
    ret = snewn(length, unsigned char);

    PUT_32BIT(ret, bignum_bitcount(key->modulus));
    pos = 4;
    pos += ssh1_write_bignum(ret + pos, key->exponent);
    pos += ssh1_write_bignum(ret + pos, key->modulus);

    *len = length;
    return ret;
}

/* Given a public blob, determine its length. */
int rsa_public_blob_len(void *data, int maxlen)
{
    unsigned char *p = (unsigned char *)data;
    int n;

    if (maxlen < 4)
	return -1;
    p += 4;			       /* length word */
    maxlen -= 4;

    n = ssh1_read_bignum(p, maxlen, NULL);    /* exponent */
    if (n < 0)
	return -1;
    p += n;

    n = ssh1_read_bignum(p, maxlen, NULL);    /* modulus */
    if (n < 0)
	return -1;
    p += n;

    return p - (unsigned char *)data;
}