X-Git-Url: https://git.distorted.org.uk/u/mdw/putty/blobdiff_plain/a52f067e0510f49ff0473878280521bd11cd3c78..HEAD:/sshrsa.c diff --git a/sshrsa.c b/sshrsa.c index 324fbd1d..4ec95f23 100644 --- a/sshrsa.c +++ b/sshrsa.c @@ -1,54 +1,32 @@ /* - * RSA implementation just sufficient for ssh client-side - * initialisation step - * - * Rewritten for more speed by Joris van Rantwijk, Jun 1999. + * RSA implementation for PuTTY. */ #include #include #include - -#if defined TESTMODE || defined RSADEBUG -#ifndef DLVL -#define DLVL 10000 -#endif -#define debug(x) bndebug(#x,x) -static int level = 0; -static void bndebug(char *name, Bignum b) { - int i; - int w = 50-level-strlen(name)-5*b[0]; - if (level >= DLVL) - return; - if (w < 0) w = 0; - dprintf("%*s%s%*s", level, "", name, w, ""); - for (i=b[0]; i>0; i--) - dprintf(" %04x", b[i]); - dprintf("\n"); -} -#define dmsg(x) do {if(level #include "ssh.h" +#include "misc.h" -int makekey(unsigned char *data, struct RSAKey *result, - unsigned char **keystr, int order) { +int makekey(unsigned char *data, int len, struct RSAKey *result, + unsigned char **keystr, int order) +{ unsigned char *p = data; - int i; + 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++; + result->bits = 0; + for (i = 0; i < 4; i++) + result->bits = (result->bits << 8) + *p++; } else - p += 4; + p += 4; + + len -= 4; /* * order=0 means exponent then modulus (the keys sent by the @@ -56,153 +34,1071 @@ int makekey(unsigned char *data, struct RSAKey *result, * stored in a keyfile). */ - if (order == 0) - p += ssh1_read_bignum(p, result ? &result->exponent : NULL); + 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 = (((p[0] << 8) + p[1]) + 7) / 8; - if (keystr) *keystr = p+2; - p += ssh1_read_bignum(p, result ? &result->modulus : NULL); - if (order == 1) - p += ssh1_read_bignum(p, result ? &result->exponent : NULL); + 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, struct RSAKey *result) { - return ssh1_read_bignum(data, &result->private_exponent); +int makeprivate(unsigned char *data, int len, struct RSAKey *result) +{ + return ssh1_read_bignum(data, len, &result->private_exponent); } -void rsaencrypt(unsigned char *data, int length, struct RSAKey *key) { +int rsaencrypt(unsigned char *data, int length, struct RSAKey *key) +{ Bignum b1, b2; - int w, i; + int i; unsigned char *p; - debug(key->exponent); + if (key->bytes < length + 4) + return 0; /* RSA key too short! */ - memmove(data+key->bytes-length, data, length); + memmove(data + key->bytes - length, data, length); data[0] = 0; data[1] = 2; - for (i = 2; i < key->bytes-length-1; i++) { + for (i = 2; i < key->bytes - length - 1; i++) { do { data[i] = random_byte(); } while (data[i] == 0); } - data[key->bytes-length-1] = 0; + data[key->bytes - length - 1] = 0; - w = (key->bytes+1)/2; + b1 = bignum_from_bytes(data, key->bytes); - b1 = newbn(w); - b2 = newbn(w); + b2 = modpow(b1, key->exponent, key->modulus); p = data; - for (i=1; i<=w; i++) - b1[i] = 0; - for (i=key->bytes; i-- ;) { - unsigned char byte = *p++; - if (i & 1) - b1[1+i/2] |= byte<<8; - else - b1[1+i/2] |= byte; + for (i = key->bytes; i--;) { + *p++ = bignum_byte(b2, i); } - debug(b1); + freebn(b1); + freebn(b2); - modpow(b1, key->exponent, key->modulus, b2); + return 1; +} - debug(b2); +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); + } + smemclr(lenbuf, sizeof(lenbuf)); +} - p = data; - for (i=key->bytes; i-- ;) { - unsigned char b; - if (i & 1) - b = b2[1+i/2] >> 8; - else - b = b2[1+i/2] & 0xFF; - *p++ = b; +/* + * Compute (base ^ exp) % mod, provided mod == p * q, with p,q + * distinct primes, and iqmp is the multiplicative inverse of q mod p. + * Uses Chinese Remainder Theorem to speed computation up over the + * obvious implementation of a single big modpow. + */ +Bignum crt_modpow(Bignum base, Bignum exp, Bignum mod, + Bignum p, Bignum q, Bignum iqmp) +{ + Bignum pm1, qm1, pexp, qexp, presult, qresult, diff, multiplier, ret0, ret; + + /* + * Reduce the exponent mod phi(p) and phi(q), to save time when + * exponentiating mod p and mod q respectively. Of course, since p + * and q are prime, phi(p) == p-1 and similarly for q. + */ + pm1 = copybn(p); + decbn(pm1); + qm1 = copybn(q); + decbn(qm1); + pexp = bigmod(exp, pm1); + qexp = bigmod(exp, qm1); + + /* + * Do the two modpows. + */ + presult = modpow(base, pexp, p); + qresult = modpow(base, qexp, q); + + /* + * Recombine the results. We want a value which is congruent to + * qresult mod q, and to presult mod p. + * + * We know that iqmp * q is congruent to 1 * mod p (by definition + * of iqmp) and to 0 mod q (obviously). So we start with qresult + * (which is congruent to qresult mod both primes), and add on + * (presult-qresult) * (iqmp * q) which adjusts it to be congruent + * to presult mod p without affecting its value mod q. + */ + if (bignum_cmp(presult, qresult) < 0) { + /* + * Can't subtract presult from qresult without first adding on + * p. + */ + Bignum tmp = presult; + presult = bigadd(presult, p); + freebn(tmp); } + diff = bigsub(presult, qresult); + multiplier = bigmul(iqmp, q); + ret0 = bigmuladd(multiplier, diff, qresult); - freebn(b1); - freebn(b2); + /* + * Finally, reduce the result mod n. + */ + ret = bigmod(ret0, mod); + + /* + * Free all the intermediate results before returning. + */ + freebn(pm1); + freebn(qm1); + freebn(pexp); + freebn(qexp); + freebn(presult); + freebn(qresult); + freebn(diff); + freebn(multiplier); + freebn(ret0); + + return ret; } -Bignum rsadecrypt(Bignum input, struct RSAKey *key) { +/* + * This function is a wrapper on modpow(). It has the same effect as + * modpow(), but employs RSA blinding to protect against timing + * attacks and also uses the Chinese Remainder Theorem (implemented + * above, in crt_modpow()) to speed up the main operation. + */ +static Bignum rsa_privkey_op(Bignum input, struct RSAKey *key) +{ + Bignum random, random_encrypted, random_inverse; + Bignum input_blinded, ret_blinded; Bignum ret; - ret = newbn(key->modulus[0]); - modpow(input, key->private_exponent, key->modulus, 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; + } + + /* + * Also, make sure it has an inverse mod modulus. + */ + random_inverse = modinv(random, key->modulus); + if (!random_inverse) { + freebn(random); + continue; + } + + 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 = crt_modpow(random, key->exponent, + key->modulus, key->p, key->q, key->iqmp); + input_blinded = modmul(input, random_encrypted, key->modulus); + ret_blinded = crt_modpow(input_blinded, key->private_exponent, + key->modulus, key->p, key->q, key->iqmp); + ret = modmul(ret_blinded, random_inverse, key->modulus); + + freebn(ret_blinded); + freebn(input_blinded); + freebn(random_inverse); + freebn(random_encrypted); + freebn(random); + return ret; } -int rsastr_len(struct RSAKey *key) { +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; - return 4 * (ex[0]+md[0]) + 10; + 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) { +void rsastr_fmt(char *str, struct RSAKey *key) +{ Bignum md, ex; - int len = 0, i; + int len = 0, i, nibbles; + static const char hex[] = "0123456789abcdef"; md = key->modulus; ex = key->exponent; - for (i=1; i<=ex[0]; i++) { - sprintf(str+len, "%04x", ex[i]); - len += strlen(str+len); + 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); } - str[len++] = '/'; - for (i=1; i<=md[0]; i++) { - sprintf(str+len, "%04x", md[i]); - len += strlen(str+len); + 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'; } - str[len] = '\0'; } -void freersakey(struct RSAKey *key) { - if (key->modulus) freebn(key->modulus); - if (key->exponent) freebn(key->exponent); - if (key->private_exponent) freebn(key->private_exponent); - if (key->comment) free(key->comment); +/* + * 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); + freebn(pm1); + cmp = bignum_cmp(ed, One); + freebn(ed); + if (cmp != 0) + return 0; + + qm1 = copybn(key->q); + decbn(qm1); + ed = modmul(key->exponent, key->private_exponent, qm1); + freebn(qm1); + cmp = bignum_cmp(ed, One); + freebn(ed); + if (cmp != 0) + return 0; + + /* + * Ensure p > q. + * + * I have seen key blobs in the wild which were generated with + * p < q, so instead of rejecting the key in this case we + * should instead flip them round into the canonical order of + * p > q. This also involves regenerating iqmp. + */ + if (bignum_cmp(key->p, key->q) <= 0) { + Bignum tmp = key->p; + key->p = key->q; + key->q = tmp; + + freebn(key->iqmp); + key->iqmp = modinv(key->q, key->p); + if (!key->iqmp) + return 0; + } + + /* + * Ensure iqmp * q is congruent to 1, modulo p. + */ + n = modmul(key->iqmp, key->q, key->p); + cmp = bignum_cmp(n, One); + freebn(n); + if (cmp != 0) + return 0; + + return 1; } -#ifdef TESTMODE +/* 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); -#ifndef NODDY -#define p1 10007 -#define p2 10069 -#define p3 10177 -#else -#define p1 3 -#define p2 7 -#define p3 13 -#endif + 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; +} -unsigned short P1[2] = { 1, p1 }; -unsigned short P2[2] = { 1, p2 }; -unsigned short P3[2] = { 1, p3 }; -unsigned short bigmod[5] = { 4, 0, 0, 0, 32768U }; -unsigned short mod[5] = { 4, 0, 0, 0, 0 }; -unsigned short a[5] = { 4, 0, 0, 0, 0 }; -unsigned short b[5] = { 4, 0, 0, 0, 0 }; -unsigned short c[5] = { 4, 0, 0, 0, 0 }; -unsigned short One[2] = { 1, 1 }; -unsigned short Two[2] = { 1, 2 }; +/* Given a public blob, determine its length. */ +int rsa_public_blob_len(void *data, int maxlen) +{ + unsigned char *p = (unsigned char *)data; + int n; -int main(void) { - modmult(P1, P2, bigmod, a); debug(a); - modmult(a, P3, bigmod, mod); debug(mod); + if (maxlen < 4) + return -1; + p += 4; /* length word */ + maxlen -= 4; - sub(P1, One, a); debug(a); - sub(P2, One, b); debug(b); - modmult(a, b, bigmod, c); debug(c); - sub(P3, One, a); debug(a); - modmult(a, c, bigmod, b); debug(b); + n = ssh1_read_bignum(p, maxlen, NULL); /* exponent */ + if (n < 0) + return -1; + p += n; - modpow(Two, b, mod, a); debug(a); + n = ssh1_read_bignum(p, maxlen, NULL); /* modulus */ + if (n < 0) + return -1; + p += n; - return 0; + return p - (unsigned char *)data; } -#endif +void freersakey(struct RSAKey *key) +{ + if (key->modulus) + freebn(key->modulus); + if (key->exponent) + freebn(key->exponent); + if (key->private_exponent) + freebn(key->private_exponent); + if (key->p) + freebn(key->p); + if (key->q) + freebn(key->q); + if (key->iqmp) + freebn(key->iqmp); + if (key->comment) + sfree(key->comment); +} + +/* ---------------------------------------------------------------------- + * Implementation of the ssh-rsa signing key type. + */ + +static void getstring(char **data, int *datalen, char **p, int *length) +{ + *p = NULL; + if (*datalen < 4) + return; + *length = toint(GET_32BIT(*data)); + if (*length < 0) + return; + *datalen -= 4; + *data += 4; + if (*datalen < *length) + return; + *p = *data; + *data += *length; + *datalen -= *length; +} +static Bignum getmp(char **data, int *datalen) +{ + char *p; + int length; + Bignum b; + + getstring(data, datalen, &p, &length); + if (!p) + return NULL; + b = bignum_from_bytes((unsigned char *)p, length); + return b; +} + +static void rsa2_freekey(void *key); /* forward reference */ + +static void *rsa2_newkey(char *data, int len) +{ + char *p; + int slen; + struct RSAKey *rsa; + + rsa = snew(struct RSAKey); + getstring(&data, &len, &p, &slen); + + if (!p || slen != 7 || memcmp(p, "ssh-rsa", 7)) { + sfree(rsa); + return NULL; + } + rsa->exponent = getmp(&data, &len); + rsa->modulus = getmp(&data, &len); + rsa->private_exponent = NULL; + rsa->p = rsa->q = rsa->iqmp = NULL; + rsa->comment = NULL; + + if (!rsa->exponent || !rsa->modulus) { + rsa2_freekey(rsa); + return NULL; + } + + return rsa; +} + +static void rsa2_freekey(void *key) +{ + struct RSAKey *rsa = (struct RSAKey *) key; + freersakey(rsa); + sfree(rsa); +} + +static char *rsa2_fmtkey(void *key) +{ + struct RSAKey *rsa = (struct RSAKey *) key; + char *p; + int len; + + len = rsastr_len(rsa); + p = snewn(len, char); + rsastr_fmt(p, rsa); + return p; +} + +static unsigned char *rsa2_public_blob(void *key, int *len) +{ + struct RSAKey *rsa = (struct RSAKey *) key; + int elen, mlen, bloblen; + int i; + unsigned char *blob, *p; + + elen = (bignum_bitcount(rsa->exponent) + 8) / 8; + mlen = (bignum_bitcount(rsa->modulus) + 8) / 8; + + /* + * string "ssh-rsa", mpint exp, mpint mod. Total 19+elen+mlen. + * (three length fields, 12+7=19). + */ + bloblen = 19 + elen + mlen; + blob = snewn(bloblen, unsigned char); + p = blob; + PUT_32BIT(p, 7); + p += 4; + memcpy(p, "ssh-rsa", 7); + p += 7; + PUT_32BIT(p, elen); + p += 4; + for (i = elen; i--;) + *p++ = bignum_byte(rsa->exponent, i); + PUT_32BIT(p, mlen); + p += 4; + for (i = mlen; i--;) + *p++ = bignum_byte(rsa->modulus, i); + assert(p == blob + bloblen); + *len = bloblen; + return blob; +} + +static unsigned char *rsa2_private_blob(void *key, int *len) +{ + struct RSAKey *rsa = (struct RSAKey *) key; + int dlen, plen, qlen, ulen, bloblen; + int i; + unsigned char *blob, *p; + + dlen = (bignum_bitcount(rsa->private_exponent) + 8) / 8; + plen = (bignum_bitcount(rsa->p) + 8) / 8; + qlen = (bignum_bitcount(rsa->q) + 8) / 8; + ulen = (bignum_bitcount(rsa->iqmp) + 8) / 8; + + /* + * mpint private_exp, mpint p, mpint q, mpint iqmp. Total 16 + + * sum of lengths. + */ + bloblen = 16 + dlen + plen + qlen + ulen; + blob = snewn(bloblen, unsigned char); + p = blob; + PUT_32BIT(p, dlen); + p += 4; + for (i = dlen; i--;) + *p++ = bignum_byte(rsa->private_exponent, i); + PUT_32BIT(p, plen); + p += 4; + for (i = plen; i--;) + *p++ = bignum_byte(rsa->p, i); + PUT_32BIT(p, qlen); + p += 4; + for (i = qlen; i--;) + *p++ = bignum_byte(rsa->q, i); + PUT_32BIT(p, ulen); + p += 4; + for (i = ulen; i--;) + *p++ = bignum_byte(rsa->iqmp, i); + assert(p == blob + bloblen); + *len = bloblen; + return blob; +} + +static void *rsa2_createkey(unsigned char *pub_blob, int pub_len, + unsigned char *priv_blob, int priv_len) +{ + struct RSAKey *rsa; + char *pb = (char *) priv_blob; + + rsa = rsa2_newkey((char *) pub_blob, pub_len); + rsa->private_exponent = getmp(&pb, &priv_len); + rsa->p = getmp(&pb, &priv_len); + rsa->q = getmp(&pb, &priv_len); + rsa->iqmp = getmp(&pb, &priv_len); + + if (!rsa_verify(rsa)) { + rsa2_freekey(rsa); + return NULL; + } + + return rsa; +} + +static void *rsa2_openssh_createkey(unsigned char **blob, int *len) +{ + char **b = (char **) blob; + struct RSAKey *rsa; + + rsa = snew(struct RSAKey); + rsa->comment = NULL; + + rsa->modulus = getmp(b, len); + rsa->exponent = getmp(b, len); + rsa->private_exponent = getmp(b, len); + rsa->iqmp = getmp(b, len); + rsa->p = getmp(b, len); + rsa->q = getmp(b, len); + + if (!rsa->modulus || !rsa->exponent || !rsa->private_exponent || + !rsa->iqmp || !rsa->p || !rsa->q) { + rsa2_freekey(rsa); + return NULL; + } + + if (!rsa_verify(rsa)) { + rsa2_freekey(rsa); + return NULL; + } + + return rsa; +} + +static int rsa2_openssh_fmtkey(void *key, unsigned char *blob, int len) +{ + struct RSAKey *rsa = (struct RSAKey *) key; + int bloblen, i; + + bloblen = + ssh2_bignum_length(rsa->modulus) + + ssh2_bignum_length(rsa->exponent) + + ssh2_bignum_length(rsa->private_exponent) + + ssh2_bignum_length(rsa->iqmp) + + ssh2_bignum_length(rsa->p) + ssh2_bignum_length(rsa->q); + + if (bloblen > len) + return bloblen; + + bloblen = 0; +#define ENC(x) \ + PUT_32BIT(blob+bloblen, ssh2_bignum_length((x))-4); bloblen += 4; \ + for (i = ssh2_bignum_length((x))-4; i-- ;) blob[bloblen++]=bignum_byte((x),i); + ENC(rsa->modulus); + ENC(rsa->exponent); + ENC(rsa->private_exponent); + ENC(rsa->iqmp); + ENC(rsa->p); + ENC(rsa->q); + + return bloblen; +} + +static int rsa2_pubkey_bits(void *blob, int len) +{ + struct RSAKey *rsa; + int ret; + + rsa = rsa2_newkey((char *) blob, len); + ret = bignum_bitcount(rsa->modulus); + rsa2_freekey(rsa); + + return ret; +} + +static char *rsa2_fingerprint(void *key) +{ + struct RSAKey *rsa = (struct RSAKey *) key; + struct MD5Context md5c; + unsigned char digest[16], lenbuf[4]; + char buffer[16 * 3 + 40]; + char *ret; + int numlen, i; + + MD5Init(&md5c); + MD5Update(&md5c, (unsigned char *)"\0\0\0\7ssh-rsa", 11); + +#define ADD_BIGNUM(bignum) \ + numlen = (bignum_bitcount(bignum)+8)/8; \ + PUT_32BIT(lenbuf, numlen); MD5Update(&md5c, lenbuf, 4); \ + for (i = numlen; i-- ;) { \ + unsigned char c = bignum_byte(bignum, i); \ + MD5Update(&md5c, &c, 1); \ + } + ADD_BIGNUM(rsa->exponent); + ADD_BIGNUM(rsa->modulus); +#undef ADD_BIGNUM + + MD5Final(digest, &md5c); + + sprintf(buffer, "ssh-rsa %d ", bignum_bitcount(rsa->modulus)); + for (i = 0; i < 16; i++) + sprintf(buffer + strlen(buffer), "%s%02x", i ? ":" : "", + digest[i]); + ret = snewn(strlen(buffer) + 1, char); + if (ret) + strcpy(ret, buffer); + return ret; +} + +/* + * This is the magic ASN.1/DER prefix that goes in the decoded + * signature, between the string of FFs and the actual SHA hash + * value. The meaning of it is: + * + * 00 -- this marks the end of the FFs; not part of the ASN.1 bit itself + * + * 30 21 -- a constructed SEQUENCE of length 0x21 + * 30 09 -- a constructed sub-SEQUENCE of length 9 + * 06 05 -- an object identifier, length 5 + * 2B 0E 03 02 1A -- object id { 1 3 14 3 2 26 } + * (the 1,3 comes from 0x2B = 43 = 40*1+3) + * 05 00 -- NULL + * 04 14 -- a primitive OCTET STRING of length 0x14 + * [0x14 bytes of hash data follows] + * + * The object id in the middle there is listed as `id-sha1' in + * ftp://ftp.rsasecurity.com/pub/pkcs/pkcs-1/pkcs-1v2-1d2.asn (the + * ASN module for PKCS #1) and its expanded form is as follows: + * + * id-sha1 OBJECT IDENTIFIER ::= { + * iso(1) identified-organization(3) oiw(14) secsig(3) + * algorithms(2) 26 } + */ +static const unsigned char asn1_weird_stuff[] = { + 0x00, 0x30, 0x21, 0x30, 0x09, 0x06, 0x05, 0x2B, + 0x0E, 0x03, 0x02, 0x1A, 0x05, 0x00, 0x04, 0x14, +}; + +#define ASN1_LEN ( (int) sizeof(asn1_weird_stuff) ) + +static int rsa2_verifysig(void *key, char *sig, int siglen, + char *data, int datalen) +{ + struct RSAKey *rsa = (struct RSAKey *) key; + Bignum in, out; + char *p; + int slen; + int bytes, i, j, ret; + unsigned char hash[20]; + + getstring(&sig, &siglen, &p, &slen); + if (!p || slen != 7 || memcmp(p, "ssh-rsa", 7)) { + return 0; + } + in = getmp(&sig, &siglen); + if (!in) + return 0; + out = modpow(in, rsa->exponent, rsa->modulus); + freebn(in); + + ret = 1; + + bytes = (bignum_bitcount(rsa->modulus)+7) / 8; + /* Top (partial) byte should be zero. */ + if (bignum_byte(out, bytes - 1) != 0) + ret = 0; + /* First whole byte should be 1. */ + if (bignum_byte(out, bytes - 2) != 1) + ret = 0; + /* Most of the rest should be FF. */ + for (i = bytes - 3; i >= 20 + ASN1_LEN; i--) { + if (bignum_byte(out, i) != 0xFF) + ret = 0; + } + /* Then we expect to see the asn1_weird_stuff. */ + for (i = 20 + ASN1_LEN - 1, j = 0; i >= 20; i--, j++) { + if (bignum_byte(out, i) != asn1_weird_stuff[j]) + ret = 0; + } + /* Finally, we expect to see the SHA-1 hash of the signed data. */ + SHA_Simple(data, datalen, hash); + for (i = 19, j = 0; i >= 0; i--, j++) { + if (bignum_byte(out, i) != hash[j]) + ret = 0; + } + freebn(out); + + return ret; +} + +static unsigned char *rsa2_sign(void *key, char *data, int datalen, + int *siglen) +{ + struct RSAKey *rsa = (struct RSAKey *) key; + unsigned char *bytes; + int nbytes; + unsigned char hash[20]; + Bignum in, out; + int i, j; + + SHA_Simple(data, datalen, hash); + + nbytes = (bignum_bitcount(rsa->modulus) - 1) / 8; + assert(1 <= nbytes - 20 - ASN1_LEN); + bytes = snewn(nbytes, unsigned char); + + bytes[0] = 1; + for (i = 1; i < nbytes - 20 - ASN1_LEN; i++) + bytes[i] = 0xFF; + for (i = nbytes - 20 - ASN1_LEN, j = 0; i < nbytes - 20; i++, j++) + bytes[i] = asn1_weird_stuff[j]; + for (i = nbytes - 20, j = 0; i < nbytes; i++, j++) + bytes[i] = hash[j]; + + in = bignum_from_bytes(bytes, nbytes); + sfree(bytes); + + out = rsa_privkey_op(in, rsa); + freebn(in); + + nbytes = (bignum_bitcount(out) + 7) / 8; + bytes = snewn(4 + 7 + 4 + nbytes, unsigned char); + PUT_32BIT(bytes, 7); + memcpy(bytes + 4, "ssh-rsa", 7); + PUT_32BIT(bytes + 4 + 7, nbytes); + for (i = 0; i < nbytes; i++) + bytes[4 + 7 + 4 + i] = bignum_byte(out, nbytes - 1 - i); + freebn(out); + + *siglen = 4 + 7 + 4 + nbytes; + return bytes; +} + +const struct ssh_signkey ssh_rsa = { + rsa2_newkey, + rsa2_freekey, + rsa2_fmtkey, + rsa2_public_blob, + rsa2_private_blob, + rsa2_createkey, + rsa2_openssh_createkey, + rsa2_openssh_fmtkey, + rsa2_pubkey_bits, + rsa2_fingerprint, + rsa2_verifysig, + rsa2_sign, + "ssh-rsa", + "rsa2" +}; + +void *ssh_rsakex_newkey(char *data, int len) +{ + return rsa2_newkey(data, len); +} + +void ssh_rsakex_freekey(void *key) +{ + rsa2_freekey(key); +} + +int ssh_rsakex_klen(void *key) +{ + struct RSAKey *rsa = (struct RSAKey *) key; + + return bignum_bitcount(rsa->modulus); +} + +static void oaep_mask(const struct ssh_hash *h, void *seed, int seedlen, + void *vdata, int datalen) +{ + unsigned char *data = (unsigned char *)vdata; + unsigned count = 0; + + while (datalen > 0) { + int i, max = (datalen > h->hlen ? h->hlen : datalen); + void *s; + unsigned char counter[4], hash[SSH2_KEX_MAX_HASH_LEN]; + + assert(h->hlen <= SSH2_KEX_MAX_HASH_LEN); + PUT_32BIT(counter, count); + s = h->init(); + h->bytes(s, seed, seedlen); + h->bytes(s, counter, 4); + h->final(s, hash); + count++; + + for (i = 0; i < max; i++) + data[i] ^= hash[i]; + + data += max; + datalen -= max; + } +} + +void ssh_rsakex_encrypt(const struct ssh_hash *h, unsigned char *in, int inlen, + unsigned char *out, int outlen, + void *key) +{ + Bignum b1, b2; + struct RSAKey *rsa = (struct RSAKey *) key; + int k, i; + char *p; + const int HLEN = h->hlen; + + /* + * Here we encrypt using RSAES-OAEP. Essentially this means: + * + * - we have a SHA-based `mask generation function' which + * creates a pseudo-random stream of mask data + * deterministically from an input chunk of data. + * + * - we have a random chunk of data called a seed. + * + * - we use the seed to generate a mask which we XOR with our + * plaintext. + * + * - then we use _the masked plaintext_ to generate a mask + * which we XOR with the seed. + * + * - then we concatenate the masked seed and the masked + * plaintext, and RSA-encrypt that lot. + * + * The result is that the data input to the encryption function + * is random-looking and (hopefully) contains no exploitable + * structure such as PKCS1-v1_5 does. + * + * For a precise specification, see RFC 3447, section 7.1.1. + * Some of the variable names below are derived from that, so + * it'd probably help to read it anyway. + */ + + /* k denotes the length in octets of the RSA modulus. */ + k = (7 + bignum_bitcount(rsa->modulus)) / 8; + + /* The length of the input data must be at most k - 2hLen - 2. */ + assert(inlen > 0 && inlen <= k - 2*HLEN - 2); + + /* The length of the output data wants to be precisely k. */ + assert(outlen == k); + + /* + * Now perform EME-OAEP encoding. First set up all the unmasked + * output data. + */ + /* Leading byte zero. */ + out[0] = 0; + /* At position 1, the seed: HLEN bytes of random data. */ + for (i = 0; i < HLEN; i++) + out[i + 1] = random_byte(); + /* At position 1+HLEN, the data block DB, consisting of: */ + /* The hash of the label (we only support an empty label here) */ + h->final(h->init(), out + HLEN + 1); + /* A bunch of zero octets */ + memset(out + 2*HLEN + 1, 0, outlen - (2*HLEN + 1)); + /* A single 1 octet, followed by the input message data. */ + out[outlen - inlen - 1] = 1; + memcpy(out + outlen - inlen, in, inlen); + + /* + * Now use the seed data to mask the block DB. + */ + oaep_mask(h, out+1, HLEN, out+HLEN+1, outlen-HLEN-1); + + /* + * And now use the masked DB to mask the seed itself. + */ + oaep_mask(h, out+HLEN+1, outlen-HLEN-1, out+1, HLEN); + + /* + * Now `out' contains precisely the data we want to + * RSA-encrypt. + */ + b1 = bignum_from_bytes(out, outlen); + b2 = modpow(b1, rsa->exponent, rsa->modulus); + p = (char *)out; + for (i = outlen; i--;) { + *p++ = bignum_byte(b2, i); + } + freebn(b1); + freebn(b2); + + /* + * And we're done. + */ +} + +static const struct ssh_kex ssh_rsa_kex_sha1 = { + "rsa1024-sha1", NULL, KEXTYPE_RSA, NULL, NULL, 0, 0, &ssh_sha1 +}; + +static const struct ssh_kex ssh_rsa_kex_sha256 = { + "rsa2048-sha256", NULL, KEXTYPE_RSA, NULL, NULL, 0, 0, &ssh_sha256 +}; + +static const struct ssh_kex *const rsa_kex_list[] = { + &ssh_rsa_kex_sha256, + &ssh_rsa_kex_sha1 +}; + +const struct ssh_kexes ssh_rsa_kex = { + sizeof(rsa_kex_list) / sizeof(*rsa_kex_list), + rsa_kex_list +};