X-Git-Url: https://git.distorted.org.uk/u/mdw/putty/blobdiff_plain/65a22376e5875181e41108028091018cdcd4fdae..22dcdc3b1a1c7c820fabe3ebaae8be6b09b4408e:/sshrsa.c diff --git a/sshrsa.c b/sshrsa.c index c9338621..fa5bfa25 100644 --- a/sshrsa.c +++ b/sshrsa.c @@ -9,8 +9,6 @@ #include #include #include -#include // FIXME -#include "putty.h" // FIXME #include "ssh.h" @@ -153,6 +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); @@ -208,7 +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; } @@ -233,7 +282,7 @@ static char *rsa2_fmtkey(void *key) { len = rsastr_len(rsa); p = smalloc(len); - rsastr_fmt(p, rsa); + rsastr_fmt(p, rsa); return p; } @@ -306,6 +355,41 @@ static void *rsa2_createkey(unsigned char *pub_blob, int pub_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; } @@ -345,23 +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; @@ -389,12 +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; } @@ -422,9 +517,9 @@ unsigned char *rsa2_sign(void *key, char *data, int datalen, int *siglen) { bytes = smalloc(nbytes); bytes[0] = 1; - for (i = 1; i < nbytes-20-sizeof(asn1_weird_stuff); i++) + for (i = 1; i < nbytes-20-ASN1_LEN; i++) bytes[i] = 0xFF; - for (i = nbytes-20-sizeof(asn1_weird_stuff), j=0; i < nbytes-20; i++,j++) + 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]; @@ -455,6 +550,7 @@ const struct ssh_signkey ssh_rsa = { rsa2_public_blob, rsa2_private_blob, rsa2_createkey, + rsa2_openssh_createkey, rsa2_fingerprint, rsa2_verifysig, rsa2_sign,