X-Git-Url: https://git.distorted.org.uk/u/mdw/putty/blobdiff_plain/5d03233bc14bfcf7a60ce2364cbd9e6a732ce8d6..defab6b847906338311fae6ff37e8b6985c5ac08:/sshrsa.c diff --git a/sshrsa.c b/sshrsa.c index 63439447..fa5bfa25 100644 --- a/sshrsa.c +++ b/sshrsa.c @@ -8,6 +8,7 @@ #include #include #include +#include #include "ssh.h" @@ -150,6 +151,57 @@ void rsa_fingerprint(char *str, int len, struct RSAKey *key) { } } +/* + * 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; +} + void freersakey(struct RSAKey *key) { if (key->modulus) freebn(key->modulus); if (key->exponent) freebn(key->exponent); @@ -205,7 +257,7 @@ static void *rsa2_newkey(char *data, int len) { if (!rsa) return NULL; getstring(&data, &len, &p, &slen); - if (!p || memcmp(p, "ssh-rsa", 7)) { + if (!p || slen != 7 || memcmp(p, "ssh-rsa", 7)) { sfree(rsa); return NULL; } @@ -230,10 +282,117 @@ static char *rsa2_fmtkey(void *key) { len = rsastr_len(rsa); p = smalloc(len); - rsastr_fmt(p, rsa); + 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 = (ssh1_bignum_bitcount(rsa->exponent)+8)/8; + mlen = (ssh1_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 = smalloc(bloblen); + 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 = (ssh1_bignum_bitcount(rsa->private_exponent)+8)/8; + plen = (ssh1_bignum_bitcount(rsa->p)+8)/8; + qlen = (ssh1_bignum_bitcount(rsa->q)+8)/8; + ulen = (ssh1_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 = smalloc(bloblen); + 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 = smalloc(sizeof(struct RSAKey)); + if (!rsa) return NULL; + 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) { + sfree(rsa->modulus); + sfree(rsa->exponent); + sfree(rsa->private_exponent); + sfree(rsa->iqmp); + sfree(rsa->p); + sfree(rsa->q); + sfree(rsa); + return NULL; + } + + return rsa; +} + static char *rsa2_fingerprint(void *key) { struct RSAKey *rsa = (struct RSAKey *)key; struct MD5Context md5c; @@ -270,23 +429,34 @@ static char *rsa2_fingerprint(void *key) { /* * 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. As closely as I can tell, the meaning of it is: + * 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 -- + * 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 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; @@ -314,12 +484,12 @@ static int rsa2_verifysig(void *key, char *sig, int siglen, if (bignum_byte(out, bytes-2) != 1) ret = 0; /* Most of the rest should be FF. */ - for (i = bytes-3; i >= 20 + sizeof(asn1_weird_stuff); i--) { + 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 + sizeof(asn1_weird_stuff) - 1, j=0; i >= 20; i--,j++) { + for (i = 20 + ASN1_LEN - 1, j=0; i >= 20; i--,j++) { if (bignum_byte(out, i) != asn1_weird_stuff[j]) ret = 0; } @@ -333,15 +503,54 @@ static int rsa2_verifysig(void *key, char *sig, int siglen, return ret; } -int rsa2_sign(void *key, char *sig, int siglen, - char *data, int datalen) { - return 0; /* FIXME */ +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 = (ssh1_bignum_bitcount(rsa->modulus)-1) / 8; + bytes = smalloc(nbytes); + + 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 = modpow(in, rsa->private_exponent, rsa->modulus); + freebn(in); + + nbytes = (ssh1_bignum_bitcount(out)+7)/8; + bytes = smalloc(4+7+4+nbytes); + 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; } -struct ssh_signkey ssh_rsa = { +const struct ssh_signkey ssh_rsa = { rsa2_newkey, rsa2_freekey, rsa2_fmtkey, + rsa2_public_blob, + rsa2_private_blob, + rsa2_createkey, + rsa2_openssh_createkey, rsa2_fingerprint, rsa2_verifysig, rsa2_sign,