2 * RSA implementation for PuTTY.
13 int makekey(unsigned char *data
, int len
, struct RSAKey
*result
,
14 unsigned char **keystr
, int order
)
16 unsigned char *p
= data
;
24 for (i
= 0; i
< 4; i
++)
25 result
->bits
= (result
->bits
<< 8) + *p
++;
32 * order=0 means exponent then modulus (the keys sent by the
33 * server). order=1 means modulus then exponent (the keys
34 * stored in a keyfile).
38 n
= ssh1_read_bignum(p
, len
, result ?
&result
->exponent
: NULL
);
44 n
= ssh1_read_bignum(p
, len
, result ?
&result
->modulus
: NULL
);
45 if (n
< 0 || (result
&& bignum_bitcount(result
->modulus
) == 0)) return -1;
47 result
->bytes
= n
- 2;
54 n
= ssh1_read_bignum(p
, len
, result ?
&result
->exponent
: NULL
);
62 int makeprivate(unsigned char *data
, int len
, struct RSAKey
*result
)
64 return ssh1_read_bignum(data
, len
, &result
->private_exponent
);
67 int rsaencrypt(unsigned char *data
, int length
, struct RSAKey
*key
)
73 if (key
->bytes
< length
+ 4)
74 return 0; /* RSA key too short! */
76 memmove(data
+ key
->bytes
- length
, data
, length
);
80 for (i
= 2; i
< key
->bytes
- length
- 1; i
++) {
82 data
[i
] = random_byte();
83 } while (data
[i
] == 0);
85 data
[key
->bytes
- length
- 1] = 0;
87 b1
= bignum_from_bytes(data
, key
->bytes
);
89 b2
= modpow(b1
, key
->exponent
, key
->modulus
);
92 for (i
= key
->bytes
; i
--;) {
93 *p
++ = bignum_byte(b2
, i
);
102 static void sha512_mpint(SHA512_State
* s
, Bignum b
)
104 unsigned char lenbuf
[4];
106 len
= (bignum_bitcount(b
) + 8) / 8;
107 PUT_32BIT(lenbuf
, len
);
108 SHA512_Bytes(s
, lenbuf
, 4);
110 lenbuf
[0] = bignum_byte(b
, len
);
111 SHA512_Bytes(s
, lenbuf
, 1);
113 smemclr(lenbuf
, sizeof(lenbuf
));
117 * Compute (base ^ exp) % mod, provided mod == p * q, with p,q
118 * distinct primes, and iqmp is the multiplicative inverse of q mod p.
119 * Uses Chinese Remainder Theorem to speed computation up over the
120 * obvious implementation of a single big modpow.
122 Bignum
crt_modpow(Bignum base
, Bignum exp
, Bignum mod
,
123 Bignum p
, Bignum q
, Bignum iqmp
)
125 Bignum pm1
, qm1
, pexp
, qexp
, presult
, qresult
, diff
, multiplier
, ret0
, ret
;
128 * Reduce the exponent mod phi(p) and phi(q), to save time when
129 * exponentiating mod p and mod q respectively. Of course, since p
130 * and q are prime, phi(p) == p-1 and similarly for q.
136 pexp
= bigmod(exp
, pm1
);
137 qexp
= bigmod(exp
, qm1
);
140 * Do the two modpows.
142 presult
= modpow(base
, pexp
, p
);
143 qresult
= modpow(base
, qexp
, q
);
146 * Recombine the results. We want a value which is congruent to
147 * qresult mod q, and to presult mod p.
149 * We know that iqmp * q is congruent to 1 * mod p (by definition
150 * of iqmp) and to 0 mod q (obviously). So we start with qresult
151 * (which is congruent to qresult mod both primes), and add on
152 * (presult-qresult) * (iqmp * q) which adjusts it to be congruent
153 * to presult mod p without affecting its value mod q.
155 if (bignum_cmp(presult
, qresult
) < 0) {
157 * Can't subtract presult from qresult without first adding on
160 Bignum tmp
= presult
;
161 presult
= bigadd(presult
, p
);
164 diff
= bigsub(presult
, qresult
);
165 multiplier
= bigmul(iqmp
, q
);
166 ret0
= bigmuladd(multiplier
, diff
, qresult
);
169 * Finally, reduce the result mod n.
171 ret
= bigmod(ret0
, mod
);
174 * Free all the intermediate results before returning.
190 * This function is a wrapper on modpow(). It has the same effect as
191 * modpow(), but employs RSA blinding to protect against timing
192 * attacks and also uses the Chinese Remainder Theorem (implemented
193 * above, in crt_modpow()) to speed up the main operation.
195 static Bignum
rsa_privkey_op(Bignum input
, struct RSAKey
*key
)
197 Bignum random
, random_encrypted
, random_inverse
;
198 Bignum input_blinded
, ret_blinded
;
202 unsigned char digest512
[64];
203 int digestused
= lenof(digest512
);
207 * Start by inventing a random number chosen uniformly from the
208 * range 2..modulus-1. (We do this by preparing a random number
209 * of the right length and retrying if it's greater than the
210 * modulus, to prevent any potential Bleichenbacher-like
211 * attacks making use of the uneven distribution within the
212 * range that would arise from just reducing our number mod n.
213 * There are timing implications to the potential retries, of
214 * course, but all they tell you is the modulus, which you
217 * To preserve determinism and avoid Pageant needing to share
218 * the random number pool, we actually generate this `random'
219 * number by hashing stuff with the private key.
222 int bits
, byte
, bitsleft
, v
;
223 random
= copybn(key
->modulus
);
225 * Find the topmost set bit. (This function will return its
226 * index plus one.) Then we'll set all bits from that one
227 * downwards randomly.
229 bits
= bignum_bitcount(random
);
236 * Conceptually the following few lines are equivalent to
237 * byte = random_byte();
239 if (digestused
>= lenof(digest512
)) {
240 unsigned char seqbuf
[4];
241 PUT_32BIT(seqbuf
, hashseq
);
243 SHA512_Bytes(&ss
, "RSA deterministic blinding", 26);
244 SHA512_Bytes(&ss
, seqbuf
, sizeof(seqbuf
));
245 sha512_mpint(&ss
, key
->private_exponent
);
246 SHA512_Final(&ss
, digest512
);
250 * Now hash that digest plus the signature
254 SHA512_Bytes(&ss
, digest512
, sizeof(digest512
));
255 sha512_mpint(&ss
, input
);
256 SHA512_Final(&ss
, digest512
);
260 byte
= digest512
[digestused
++];
265 bignum_set_bit(random
, bits
, v
);
269 * Now check that this number is strictly greater than
270 * zero, and strictly less than modulus.
272 if (bignum_cmp(random
, Zero
) <= 0 ||
273 bignum_cmp(random
, key
->modulus
) >= 0) {
279 * Also, make sure it has an inverse mod modulus.
281 random_inverse
= modinv(random
, key
->modulus
);
282 if (!random_inverse
) {
291 * RSA blinding relies on the fact that (xy)^d mod n is equal
292 * to (x^d mod n) * (y^d mod n) mod n. We invent a random pair
293 * y and y^d; then we multiply x by y, raise to the power d mod
294 * n as usual, and divide by y^d to recover x^d. Thus an
295 * attacker can't correlate the timing of the modpow with the
296 * input, because they don't know anything about the number
297 * that was input to the actual modpow.
299 * The clever bit is that we don't have to do a huge modpow to
300 * get y and y^d; we will use the number we just invented as
301 * _y^d_, and use the _public_ exponent to compute (y^d)^e = y
302 * from it, which is much faster to do.
304 random_encrypted
= crt_modpow(random
, key
->exponent
,
305 key
->modulus
, key
->p
, key
->q
, key
->iqmp
);
306 input_blinded
= modmul(input
, random_encrypted
, key
->modulus
);
307 ret_blinded
= crt_modpow(input_blinded
, key
->private_exponent
,
308 key
->modulus
, key
->p
, key
->q
, key
->iqmp
);
309 ret
= modmul(ret_blinded
, random_inverse
, key
->modulus
);
312 freebn(input_blinded
);
313 freebn(random_inverse
);
314 freebn(random_encrypted
);
320 Bignum
rsadecrypt(Bignum input
, struct RSAKey
*key
)
322 return rsa_privkey_op(input
, key
);
325 int rsastr_len(struct RSAKey
*key
)
332 mdlen
= (bignum_bitcount(md
) + 15) / 16;
333 exlen
= (bignum_bitcount(ex
) + 15) / 16;
334 return 4 * (mdlen
+ exlen
) + 20;
337 void rsastr_fmt(char *str
, struct RSAKey
*key
)
340 int len
= 0, i
, nibbles
;
341 static const char hex
[] = "0123456789abcdef";
346 len
+= sprintf(str
+ len
, "0x");
348 nibbles
= (3 + bignum_bitcount(ex
)) / 4;
351 for (i
= nibbles
; i
--;)
352 str
[len
++] = hex
[(bignum_byte(ex
, i
/ 2) >> (4 * (i
% 2))) & 0xF];
354 len
+= sprintf(str
+ len
, ",0x");
356 nibbles
= (3 + bignum_bitcount(md
)) / 4;
359 for (i
= nibbles
; i
--;)
360 str
[len
++] = hex
[(bignum_byte(md
, i
/ 2) >> (4 * (i
% 2))) & 0xF];
366 * Generate a fingerprint string for the key. Compatible with the
367 * OpenSSH fingerprint code.
369 void rsa_fingerprint(char *str
, int len
, struct RSAKey
*key
)
371 struct MD5Context md5c
;
372 unsigned char digest
[16];
373 char buffer
[16 * 3 + 40];
377 numlen
= ssh1_bignum_length(key
->modulus
) - 2;
378 for (i
= numlen
; i
--;) {
379 unsigned char c
= bignum_byte(key
->modulus
, i
);
380 MD5Update(&md5c
, &c
, 1);
382 numlen
= ssh1_bignum_length(key
->exponent
) - 2;
383 for (i
= numlen
; i
--;) {
384 unsigned char c
= bignum_byte(key
->exponent
, i
);
385 MD5Update(&md5c
, &c
, 1);
387 MD5Final(digest
, &md5c
);
389 sprintf(buffer
, "%d ", bignum_bitcount(key
->modulus
));
390 for (i
= 0; i
< 16; i
++)
391 sprintf(buffer
+ strlen(buffer
), "%s%02x", i ?
":" : "",
393 strncpy(str
, buffer
, len
);
396 if (key
->comment
&& slen
< len
- 1) {
398 strncpy(str
+ slen
+ 1, key
->comment
, len
- slen
- 1);
404 * Verify that the public data in an RSA key matches the private
405 * data. We also check the private data itself: we ensure that p >
406 * q and that iqmp really is the inverse of q mod p.
408 int rsa_verify(struct RSAKey
*key
)
410 Bignum n
, ed
, pm1
, qm1
;
413 /* n must equal pq. */
414 n
= bigmul(key
->p
, key
->q
);
415 cmp
= bignum_cmp(n
, key
->modulus
);
420 /* e * d must be congruent to 1, modulo (p-1) and modulo (q-1). */
421 pm1
= copybn(key
->p
);
423 ed
= modmul(key
->exponent
, key
->private_exponent
, pm1
);
425 cmp
= bignum_cmp(ed
, One
);
430 qm1
= copybn(key
->q
);
432 ed
= modmul(key
->exponent
, key
->private_exponent
, qm1
);
434 cmp
= bignum_cmp(ed
, One
);
442 * I have seen key blobs in the wild which were generated with
443 * p < q, so instead of rejecting the key in this case we
444 * should instead flip them round into the canonical order of
445 * p > q. This also involves regenerating iqmp.
447 if (bignum_cmp(key
->p
, key
->q
) <= 0) {
453 key
->iqmp
= modinv(key
->q
, key
->p
);
459 * Ensure iqmp * q is congruent to 1, modulo p.
461 n
= modmul(key
->iqmp
, key
->q
, key
->p
);
462 cmp
= bignum_cmp(n
, One
);
470 /* Public key blob as used by Pageant: exponent before modulus. */
471 unsigned char *rsa_public_blob(struct RSAKey
*key
, int *len
)
476 length
= (ssh1_bignum_length(key
->modulus
) +
477 ssh1_bignum_length(key
->exponent
) + 4);
478 ret
= snewn(length
, unsigned char);
480 PUT_32BIT(ret
, bignum_bitcount(key
->modulus
));
482 pos
+= ssh1_write_bignum(ret
+ pos
, key
->exponent
);
483 pos
+= ssh1_write_bignum(ret
+ pos
, key
->modulus
);
489 /* Given a public blob, determine its length. */
490 int rsa_public_blob_len(void *data
, int maxlen
)
492 unsigned char *p
= (unsigned char *)data
;
497 p
+= 4; /* length word */
500 n
= ssh1_read_bignum(p
, maxlen
, NULL
); /* exponent */
505 n
= ssh1_read_bignum(p
, maxlen
, NULL
); /* modulus */
510 return p
- (unsigned char *)data
;
513 void freersakey(struct RSAKey
*key
)
516 freebn(key
->modulus
);
518 freebn(key
->exponent
);
519 if (key
->private_exponent
)
520 freebn(key
->private_exponent
);
531 /* ----------------------------------------------------------------------
532 * Implementation of the ssh-rsa signing key type.
535 static void getstring(char **data
, int *datalen
, char **p
, int *length
)
540 *length
= toint(GET_32BIT(*data
));
545 if (*datalen
< *length
)
551 static Bignum
getmp(char **data
, int *datalen
)
557 getstring(data
, datalen
, &p
, &length
);
560 b
= bignum_from_bytes((unsigned char *)p
, length
);
564 static void *rsa2_newkey(char *data
, int len
)
570 rsa
= snew(struct RSAKey
);
571 getstring(&data
, &len
, &p
, &slen
);
573 if (!p
|| slen
!= 7 || memcmp(p
, "ssh-rsa", 7)) {
577 rsa
->exponent
= getmp(&data
, &len
);
578 rsa
->modulus
= getmp(&data
, &len
);
579 rsa
->private_exponent
= NULL
;
580 rsa
->p
= rsa
->q
= rsa
->iqmp
= NULL
;
586 static void rsa2_freekey(void *key
)
588 struct RSAKey
*rsa
= (struct RSAKey
*) key
;
593 static char *rsa2_fmtkey(void *key
)
595 struct RSAKey
*rsa
= (struct RSAKey
*) key
;
599 len
= rsastr_len(rsa
);
600 p
= snewn(len
, char);
605 static unsigned char *rsa2_public_blob(void *key
, int *len
)
607 struct RSAKey
*rsa
= (struct RSAKey
*) key
;
608 int elen
, mlen
, bloblen
;
610 unsigned char *blob
, *p
;
612 elen
= (bignum_bitcount(rsa
->exponent
) + 8) / 8;
613 mlen
= (bignum_bitcount(rsa
->modulus
) + 8) / 8;
616 * string "ssh-rsa", mpint exp, mpint mod. Total 19+elen+mlen.
617 * (three length fields, 12+7=19).
619 bloblen
= 19 + elen
+ mlen
;
620 blob
= snewn(bloblen
, unsigned char);
624 memcpy(p
, "ssh-rsa", 7);
629 *p
++ = bignum_byte(rsa
->exponent
, i
);
633 *p
++ = bignum_byte(rsa
->modulus
, i
);
634 assert(p
== blob
+ bloblen
);
639 static unsigned char *rsa2_private_blob(void *key
, int *len
)
641 struct RSAKey
*rsa
= (struct RSAKey
*) key
;
642 int dlen
, plen
, qlen
, ulen
, bloblen
;
644 unsigned char *blob
, *p
;
646 dlen
= (bignum_bitcount(rsa
->private_exponent
) + 8) / 8;
647 plen
= (bignum_bitcount(rsa
->p
) + 8) / 8;
648 qlen
= (bignum_bitcount(rsa
->q
) + 8) / 8;
649 ulen
= (bignum_bitcount(rsa
->iqmp
) + 8) / 8;
652 * mpint private_exp, mpint p, mpint q, mpint iqmp. Total 16 +
655 bloblen
= 16 + dlen
+ plen
+ qlen
+ ulen
;
656 blob
= snewn(bloblen
, unsigned char);
661 *p
++ = bignum_byte(rsa
->private_exponent
, i
);
665 *p
++ = bignum_byte(rsa
->p
, i
);
669 *p
++ = bignum_byte(rsa
->q
, i
);
673 *p
++ = bignum_byte(rsa
->iqmp
, i
);
674 assert(p
== blob
+ bloblen
);
679 static void *rsa2_createkey(unsigned char *pub_blob
, int pub_len
,
680 unsigned char *priv_blob
, int priv_len
)
683 char *pb
= (char *) priv_blob
;
685 rsa
= rsa2_newkey((char *) pub_blob
, pub_len
);
686 rsa
->private_exponent
= getmp(&pb
, &priv_len
);
687 rsa
->p
= getmp(&pb
, &priv_len
);
688 rsa
->q
= getmp(&pb
, &priv_len
);
689 rsa
->iqmp
= getmp(&pb
, &priv_len
);
691 if (!rsa_verify(rsa
)) {
699 static void *rsa2_openssh_createkey(unsigned char **blob
, int *len
)
701 char **b
= (char **) blob
;
704 rsa
= snew(struct RSAKey
);
707 rsa
->modulus
= getmp(b
, len
);
708 rsa
->exponent
= getmp(b
, len
);
709 rsa
->private_exponent
= getmp(b
, len
);
710 rsa
->iqmp
= getmp(b
, len
);
711 rsa
->p
= getmp(b
, len
);
712 rsa
->q
= getmp(b
, len
);
714 if (!rsa
->modulus
|| !rsa
->exponent
|| !rsa
->private_exponent
||
715 !rsa
->iqmp
|| !rsa
->p
|| !rsa
->q
) {
720 if (!rsa_verify(rsa
)) {
728 static int rsa2_openssh_fmtkey(void *key
, unsigned char *blob
, int len
)
730 struct RSAKey
*rsa
= (struct RSAKey
*) key
;
734 ssh2_bignum_length(rsa
->modulus
) +
735 ssh2_bignum_length(rsa
->exponent
) +
736 ssh2_bignum_length(rsa
->private_exponent
) +
737 ssh2_bignum_length(rsa
->iqmp
) +
738 ssh2_bignum_length(rsa
->p
) + ssh2_bignum_length(rsa
->q
);
745 PUT_32BIT(blob+bloblen, ssh2_bignum_length((x))-4); bloblen += 4; \
746 for (i = ssh2_bignum_length((x))-4; i-- ;) blob[bloblen++]=bignum_byte((x),i);
749 ENC(rsa
->private_exponent
);
757 static int rsa2_pubkey_bits(void *blob
, int len
)
762 rsa
= rsa2_newkey((char *) blob
, len
);
763 ret
= bignum_bitcount(rsa
->modulus
);
769 static char *rsa2_fingerprint(void *key
)
771 struct RSAKey
*rsa
= (struct RSAKey
*) key
;
772 struct MD5Context md5c
;
773 unsigned char digest
[16], lenbuf
[4];
774 char buffer
[16 * 3 + 40];
779 MD5Update(&md5c
, (unsigned char *)"\0\0\0\7ssh-rsa", 11);
781 #define ADD_BIGNUM(bignum) \
782 numlen = (bignum_bitcount(bignum)+8)/8; \
783 PUT_32BIT(lenbuf, numlen); MD5Update(&md5c, lenbuf, 4); \
784 for (i = numlen; i-- ;) { \
785 unsigned char c = bignum_byte(bignum, i); \
786 MD5Update(&md5c, &c, 1); \
788 ADD_BIGNUM(rsa
->exponent
);
789 ADD_BIGNUM(rsa
->modulus
);
792 MD5Final(digest
, &md5c
);
794 sprintf(buffer
, "ssh-rsa %d ", bignum_bitcount(rsa
->modulus
));
795 for (i
= 0; i
< 16; i
++)
796 sprintf(buffer
+ strlen(buffer
), "%s%02x", i ?
":" : "",
798 ret
= snewn(strlen(buffer
) + 1, char);
805 * This is the magic ASN.1/DER prefix that goes in the decoded
806 * signature, between the string of FFs and the actual SHA hash
807 * value. The meaning of it is:
809 * 00 -- this marks the end of the FFs; not part of the ASN.1 bit itself
811 * 30 21 -- a constructed SEQUENCE of length 0x21
812 * 30 09 -- a constructed sub-SEQUENCE of length 9
813 * 06 05 -- an object identifier, length 5
814 * 2B 0E 03 02 1A -- object id { 1 3 14 3 2 26 }
815 * (the 1,3 comes from 0x2B = 43 = 40*1+3)
817 * 04 14 -- a primitive OCTET STRING of length 0x14
818 * [0x14 bytes of hash data follows]
820 * The object id in the middle there is listed as `id-sha1' in
821 * ftp://ftp.rsasecurity.com/pub/pkcs/pkcs-1/pkcs-1v2-1d2.asn (the
822 * ASN module for PKCS #1) and its expanded form is as follows:
824 * id-sha1 OBJECT IDENTIFIER ::= {
825 * iso(1) identified-organization(3) oiw(14) secsig(3)
828 static const unsigned char asn1_weird_stuff
[] = {
829 0x00, 0x30, 0x21, 0x30, 0x09, 0x06, 0x05, 0x2B,
830 0x0E, 0x03, 0x02, 0x1A, 0x05, 0x00, 0x04, 0x14,
833 #define ASN1_LEN ( (int) sizeof(asn1_weird_stuff) )
835 static int rsa2_verifysig(void *key
, char *sig
, int siglen
,
836 char *data
, int datalen
)
838 struct RSAKey
*rsa
= (struct RSAKey
*) key
;
842 int bytes
, i
, j
, ret
;
843 unsigned char hash
[20];
845 getstring(&sig
, &siglen
, &p
, &slen
);
846 if (!p
|| slen
!= 7 || memcmp(p
, "ssh-rsa", 7)) {
849 in
= getmp(&sig
, &siglen
);
852 out
= modpow(in
, rsa
->exponent
, rsa
->modulus
);
857 bytes
= (bignum_bitcount(rsa
->modulus
)+7) / 8;
858 /* Top (partial) byte should be zero. */
859 if (bignum_byte(out
, bytes
- 1) != 0)
861 /* First whole byte should be 1. */
862 if (bignum_byte(out
, bytes
- 2) != 1)
864 /* Most of the rest should be FF. */
865 for (i
= bytes
- 3; i
>= 20 + ASN1_LEN
; i
--) {
866 if (bignum_byte(out
, i
) != 0xFF)
869 /* Then we expect to see the asn1_weird_stuff. */
870 for (i
= 20 + ASN1_LEN
- 1, j
= 0; i
>= 20; i
--, j
++) {
871 if (bignum_byte(out
, i
) != asn1_weird_stuff
[j
])
874 /* Finally, we expect to see the SHA-1 hash of the signed data. */
875 SHA_Simple(data
, datalen
, hash
);
876 for (i
= 19, j
= 0; i
>= 0; i
--, j
++) {
877 if (bignum_byte(out
, i
) != hash
[j
])
885 static unsigned char *rsa2_sign(void *key
, char *data
, int datalen
,
888 struct RSAKey
*rsa
= (struct RSAKey
*) key
;
889 unsigned char *bytes
;
891 unsigned char hash
[20];
895 SHA_Simple(data
, datalen
, hash
);
897 nbytes
= (bignum_bitcount(rsa
->modulus
) - 1) / 8;
898 assert(1 <= nbytes
- 20 - ASN1_LEN
);
899 bytes
= snewn(nbytes
, unsigned char);
902 for (i
= 1; i
< nbytes
- 20 - ASN1_LEN
; i
++)
904 for (i
= nbytes
- 20 - ASN1_LEN
, j
= 0; i
< nbytes
- 20; i
++, j
++)
905 bytes
[i
] = asn1_weird_stuff
[j
];
906 for (i
= nbytes
- 20, j
= 0; i
< nbytes
; i
++, j
++)
909 in
= bignum_from_bytes(bytes
, nbytes
);
912 out
= rsa_privkey_op(in
, rsa
);
915 nbytes
= (bignum_bitcount(out
) + 7) / 8;
916 bytes
= snewn(4 + 7 + 4 + nbytes
, unsigned char);
918 memcpy(bytes
+ 4, "ssh-rsa", 7);
919 PUT_32BIT(bytes
+ 4 + 7, nbytes
);
920 for (i
= 0; i
< nbytes
; i
++)
921 bytes
[4 + 7 + 4 + i
] = bignum_byte(out
, nbytes
- 1 - i
);
924 *siglen
= 4 + 7 + 4 + nbytes
;
928 const struct ssh_signkey ssh_rsa
= {
935 rsa2_openssh_createkey
,
945 void *ssh_rsakex_newkey(char *data
, int len
)
947 return rsa2_newkey(data
, len
);
950 void ssh_rsakex_freekey(void *key
)
955 int ssh_rsakex_klen(void *key
)
957 struct RSAKey
*rsa
= (struct RSAKey
*) key
;
959 return bignum_bitcount(rsa
->modulus
);
962 static void oaep_mask(const struct ssh_hash
*h
, void *seed
, int seedlen
,
963 void *vdata
, int datalen
)
965 unsigned char *data
= (unsigned char *)vdata
;
968 while (datalen
> 0) {
969 int i
, max
= (datalen
> h
->hlen ? h
->hlen
: datalen
);
971 unsigned char counter
[4], hash
[SSH2_KEX_MAX_HASH_LEN
];
973 assert(h
->hlen
<= SSH2_KEX_MAX_HASH_LEN
);
974 PUT_32BIT(counter
, count
);
976 h
->bytes(s
, seed
, seedlen
);
977 h
->bytes(s
, counter
, 4);
981 for (i
= 0; i
< max
; i
++)
989 void ssh_rsakex_encrypt(const struct ssh_hash
*h
, unsigned char *in
, int inlen
,
990 unsigned char *out
, int outlen
,
994 struct RSAKey
*rsa
= (struct RSAKey
*) key
;
997 const int HLEN
= h
->hlen
;
1000 * Here we encrypt using RSAES-OAEP. Essentially this means:
1002 * - we have a SHA-based `mask generation function' which
1003 * creates a pseudo-random stream of mask data
1004 * deterministically from an input chunk of data.
1006 * - we have a random chunk of data called a seed.
1008 * - we use the seed to generate a mask which we XOR with our
1011 * - then we use _the masked plaintext_ to generate a mask
1012 * which we XOR with the seed.
1014 * - then we concatenate the masked seed and the masked
1015 * plaintext, and RSA-encrypt that lot.
1017 * The result is that the data input to the encryption function
1018 * is random-looking and (hopefully) contains no exploitable
1019 * structure such as PKCS1-v1_5 does.
1021 * For a precise specification, see RFC 3447, section 7.1.1.
1022 * Some of the variable names below are derived from that, so
1023 * it'd probably help to read it anyway.
1026 /* k denotes the length in octets of the RSA modulus. */
1027 k
= (7 + bignum_bitcount(rsa
->modulus
)) / 8;
1029 /* The length of the input data must be at most k - 2hLen - 2. */
1030 assert(inlen
> 0 && inlen
<= k
- 2*HLEN
- 2);
1032 /* The length of the output data wants to be precisely k. */
1033 assert(outlen
== k
);
1036 * Now perform EME-OAEP encoding. First set up all the unmasked
1039 /* Leading byte zero. */
1041 /* At position 1, the seed: HLEN bytes of random data. */
1042 for (i
= 0; i
< HLEN
; i
++)
1043 out
[i
+ 1] = random_byte();
1044 /* At position 1+HLEN, the data block DB, consisting of: */
1045 /* The hash of the label (we only support an empty label here) */
1046 h
->final(h
->init(), out
+ HLEN
+ 1);
1047 /* A bunch of zero octets */
1048 memset(out
+ 2*HLEN
+ 1, 0, outlen
- (2*HLEN
+ 1));
1049 /* A single 1 octet, followed by the input message data. */
1050 out
[outlen
- inlen
- 1] = 1;
1051 memcpy(out
+ outlen
- inlen
, in
, inlen
);
1054 * Now use the seed data to mask the block DB.
1056 oaep_mask(h
, out
+1, HLEN
, out
+HLEN
+1, outlen
-HLEN
-1);
1059 * And now use the masked DB to mask the seed itself.
1061 oaep_mask(h
, out
+HLEN
+1, outlen
-HLEN
-1, out
+1, HLEN
);
1064 * Now `out' contains precisely the data we want to
1067 b1
= bignum_from_bytes(out
, outlen
);
1068 b2
= modpow(b1
, rsa
->exponent
, rsa
->modulus
);
1070 for (i
= outlen
; i
--;) {
1071 *p
++ = bignum_byte(b2
, i
);
1081 static const struct ssh_kex ssh_rsa_kex_sha1
= {
1082 "rsa1024-sha1", NULL
, KEXTYPE_RSA
, NULL
, NULL
, 0, 0, &ssh_sha1
1085 static const struct ssh_kex ssh_rsa_kex_sha256
= {
1086 "rsa2048-sha256", NULL
, KEXTYPE_RSA
, NULL
, NULL
, 0, 0, &ssh_sha256
1089 static const struct ssh_kex
*const rsa_kex_list
[] = {
1090 &ssh_rsa_kex_sha256
,
1094 const struct ssh_kexes ssh_rsa_kex
= {
1095 sizeof(rsa_kex_list
) / sizeof(*rsa_kex_list
),