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 memset(lenbuf
, 0, sizeof(lenbuf
));
117 * This function is a wrapper on modpow(). It has the same effect
118 * as modpow(), but employs RSA blinding to protect against timing
121 static Bignum
rsa_privkey_op(Bignum input
, struct RSAKey
*key
)
123 Bignum random
, random_encrypted
, random_inverse
;
124 Bignum input_blinded
, ret_blinded
;
128 unsigned char digest512
[64];
129 int digestused
= lenof(digest512
);
133 * Start by inventing a random number chosen uniformly from the
134 * range 2..modulus-1. (We do this by preparing a random number
135 * of the right length and retrying if it's greater than the
136 * modulus, to prevent any potential Bleichenbacher-like
137 * attacks making use of the uneven distribution within the
138 * range that would arise from just reducing our number mod n.
139 * There are timing implications to the potential retries, of
140 * course, but all they tell you is the modulus, which you
143 * To preserve determinism and avoid Pageant needing to share
144 * the random number pool, we actually generate this `random'
145 * number by hashing stuff with the private key.
148 int bits
, byte
, bitsleft
, v
;
149 random
= copybn(key
->modulus
);
151 * Find the topmost set bit. (This function will return its
152 * index plus one.) Then we'll set all bits from that one
153 * downwards randomly.
155 bits
= bignum_bitcount(random
);
162 * Conceptually the following few lines are equivalent to
163 * byte = random_byte();
165 if (digestused
>= lenof(digest512
)) {
166 unsigned char seqbuf
[4];
167 PUT_32BIT(seqbuf
, hashseq
);
169 SHA512_Bytes(&ss
, "RSA deterministic blinding", 26);
170 SHA512_Bytes(&ss
, seqbuf
, sizeof(seqbuf
));
171 sha512_mpint(&ss
, key
->private_exponent
);
172 SHA512_Final(&ss
, digest512
);
176 * Now hash that digest plus the signature
180 SHA512_Bytes(&ss
, digest512
, sizeof(digest512
));
181 sha512_mpint(&ss
, input
);
182 SHA512_Final(&ss
, digest512
);
186 byte
= digest512
[digestused
++];
191 bignum_set_bit(random
, bits
, v
);
195 * Now check that this number is strictly greater than
196 * zero, and strictly less than modulus.
198 if (bignum_cmp(random
, Zero
) <= 0 ||
199 bignum_cmp(random
, key
->modulus
) >= 0) {
208 * RSA blinding relies on the fact that (xy)^d mod n is equal
209 * to (x^d mod n) * (y^d mod n) mod n. We invent a random pair
210 * y and y^d; then we multiply x by y, raise to the power d mod
211 * n as usual, and divide by y^d to recover x^d. Thus an
212 * attacker can't correlate the timing of the modpow with the
213 * input, because they don't know anything about the number
214 * that was input to the actual modpow.
216 * The clever bit is that we don't have to do a huge modpow to
217 * get y and y^d; we will use the number we just invented as
218 * _y^d_, and use the _public_ exponent to compute (y^d)^e = y
219 * from it, which is much faster to do.
221 random_encrypted
= modpow(random
, key
->exponent
, key
->modulus
);
222 random_inverse
= modinv(random
, key
->modulus
);
223 input_blinded
= modmul(input
, random_encrypted
, key
->modulus
);
224 ret_blinded
= modpow(input_blinded
, key
->private_exponent
, key
->modulus
);
225 ret
= modmul(ret_blinded
, random_inverse
, key
->modulus
);
228 freebn(input_blinded
);
229 freebn(random_inverse
);
230 freebn(random_encrypted
);
236 Bignum
rsadecrypt(Bignum input
, struct RSAKey
*key
)
238 return rsa_privkey_op(input
, key
);
241 int rsastr_len(struct RSAKey
*key
)
248 mdlen
= (bignum_bitcount(md
) + 15) / 16;
249 exlen
= (bignum_bitcount(ex
) + 15) / 16;
250 return 4 * (mdlen
+ exlen
) + 20;
253 void rsastr_fmt(char *str
, struct RSAKey
*key
)
256 int len
= 0, i
, nibbles
;
257 static const char hex
[] = "0123456789abcdef";
262 len
+= sprintf(str
+ len
, "0x");
264 nibbles
= (3 + bignum_bitcount(ex
)) / 4;
267 for (i
= nibbles
; i
--;)
268 str
[len
++] = hex
[(bignum_byte(ex
, i
/ 2) >> (4 * (i
% 2))) & 0xF];
270 len
+= sprintf(str
+ len
, ",0x");
272 nibbles
= (3 + bignum_bitcount(md
)) / 4;
275 for (i
= nibbles
; i
--;)
276 str
[len
++] = hex
[(bignum_byte(md
, i
/ 2) >> (4 * (i
% 2))) & 0xF];
282 * Generate a fingerprint string for the key. Compatible with the
283 * OpenSSH fingerprint code.
285 void rsa_fingerprint(char *str
, int len
, struct RSAKey
*key
)
287 struct MD5Context md5c
;
288 unsigned char digest
[16];
289 char buffer
[16 * 3 + 40];
293 numlen
= ssh1_bignum_length(key
->modulus
) - 2;
294 for (i
= numlen
; i
--;) {
295 unsigned char c
= bignum_byte(key
->modulus
, i
);
296 MD5Update(&md5c
, &c
, 1);
298 numlen
= ssh1_bignum_length(key
->exponent
) - 2;
299 for (i
= numlen
; i
--;) {
300 unsigned char c
= bignum_byte(key
->exponent
, i
);
301 MD5Update(&md5c
, &c
, 1);
303 MD5Final(digest
, &md5c
);
305 sprintf(buffer
, "%d ", bignum_bitcount(key
->modulus
));
306 for (i
= 0; i
< 16; i
++)
307 sprintf(buffer
+ strlen(buffer
), "%s%02x", i ?
":" : "",
309 strncpy(str
, buffer
, len
);
312 if (key
->comment
&& slen
< len
- 1) {
314 strncpy(str
+ slen
+ 1, key
->comment
, len
- slen
- 1);
320 * Verify that the public data in an RSA key matches the private
321 * data. We also check the private data itself: we ensure that p >
322 * q and that iqmp really is the inverse of q mod p.
324 int rsa_verify(struct RSAKey
*key
)
326 Bignum n
, ed
, pm1
, qm1
;
329 /* n must equal pq. */
330 n
= bigmul(key
->p
, key
->q
);
331 cmp
= bignum_cmp(n
, key
->modulus
);
336 /* e * d must be congruent to 1, modulo (p-1) and modulo (q-1). */
337 pm1
= copybn(key
->p
);
339 ed
= modmul(key
->exponent
, key
->private_exponent
, pm1
);
340 cmp
= bignum_cmp(ed
, One
);
345 qm1
= copybn(key
->q
);
347 ed
= modmul(key
->exponent
, key
->private_exponent
, qm1
);
348 cmp
= bignum_cmp(ed
, One
);
356 * I have seen key blobs in the wild which were generated with
357 * p < q, so instead of rejecting the key in this case we
358 * should instead flip them round into the canonical order of
359 * p > q. This also involves regenerating iqmp.
361 if (bignum_cmp(key
->p
, key
->q
) <= 0) {
367 key
->iqmp
= modinv(key
->q
, key
->p
);
371 * Ensure iqmp * q is congruent to 1, modulo p.
373 n
= modmul(key
->iqmp
, key
->q
, key
->p
);
374 cmp
= bignum_cmp(n
, One
);
382 /* Public key blob as used by Pageant: exponent before modulus. */
383 unsigned char *rsa_public_blob(struct RSAKey
*key
, int *len
)
388 length
= (ssh1_bignum_length(key
->modulus
) +
389 ssh1_bignum_length(key
->exponent
) + 4);
390 ret
= snewn(length
, unsigned char);
392 PUT_32BIT(ret
, bignum_bitcount(key
->modulus
));
394 pos
+= ssh1_write_bignum(ret
+ pos
, key
->exponent
);
395 pos
+= ssh1_write_bignum(ret
+ pos
, key
->modulus
);
401 /* Given a public blob, determine its length. */
402 int rsa_public_blob_len(void *data
, int maxlen
)
404 unsigned char *p
= (unsigned char *)data
;
409 p
+= 4; /* length word */
412 n
= ssh1_read_bignum(p
, maxlen
, NULL
); /* exponent */
417 n
= ssh1_read_bignum(p
, maxlen
, NULL
); /* modulus */
422 return p
- (unsigned char *)data
;
425 void freersakey(struct RSAKey
*key
)
428 freebn(key
->modulus
);
430 freebn(key
->exponent
);
431 if (key
->private_exponent
)
432 freebn(key
->private_exponent
);
443 /* ----------------------------------------------------------------------
444 * Implementation of the ssh-rsa signing key type.
447 static void getstring(char **data
, int *datalen
, char **p
, int *length
)
452 *length
= GET_32BIT(*data
);
455 if (*datalen
< *length
)
461 static Bignum
getmp(char **data
, int *datalen
)
467 getstring(data
, datalen
, &p
, &length
);
470 b
= bignum_from_bytes((unsigned char *)p
, length
);
474 static void *rsa2_newkey(char *data
, int len
)
480 rsa
= snew(struct RSAKey
);
483 getstring(&data
, &len
, &p
, &slen
);
485 if (!p
|| slen
!= 7 || memcmp(p
, "ssh-rsa", 7)) {
489 rsa
->exponent
= getmp(&data
, &len
);
490 rsa
->modulus
= getmp(&data
, &len
);
491 rsa
->private_exponent
= NULL
;
492 rsa
->p
= rsa
->q
= rsa
->iqmp
= NULL
;
498 static void rsa2_freekey(void *key
)
500 struct RSAKey
*rsa
= (struct RSAKey
*) key
;
505 static char *rsa2_fmtkey(void *key
)
507 struct RSAKey
*rsa
= (struct RSAKey
*) key
;
511 len
= rsastr_len(rsa
);
512 p
= snewn(len
, char);
517 static unsigned char *rsa2_public_blob(void *key
, int *len
)
519 struct RSAKey
*rsa
= (struct RSAKey
*) key
;
520 int elen
, mlen
, bloblen
;
522 unsigned char *blob
, *p
;
524 elen
= (bignum_bitcount(rsa
->exponent
) + 8) / 8;
525 mlen
= (bignum_bitcount(rsa
->modulus
) + 8) / 8;
528 * string "ssh-rsa", mpint exp, mpint mod. Total 19+elen+mlen.
529 * (three length fields, 12+7=19).
531 bloblen
= 19 + elen
+ mlen
;
532 blob
= snewn(bloblen
, unsigned char);
536 memcpy(p
, "ssh-rsa", 7);
541 *p
++ = bignum_byte(rsa
->exponent
, i
);
545 *p
++ = bignum_byte(rsa
->modulus
, i
);
546 assert(p
== blob
+ bloblen
);
551 static unsigned char *rsa2_private_blob(void *key
, int *len
)
553 struct RSAKey
*rsa
= (struct RSAKey
*) key
;
554 int dlen
, plen
, qlen
, ulen
, bloblen
;
556 unsigned char *blob
, *p
;
558 dlen
= (bignum_bitcount(rsa
->private_exponent
) + 8) / 8;
559 plen
= (bignum_bitcount(rsa
->p
) + 8) / 8;
560 qlen
= (bignum_bitcount(rsa
->q
) + 8) / 8;
561 ulen
= (bignum_bitcount(rsa
->iqmp
) + 8) / 8;
564 * mpint private_exp, mpint p, mpint q, mpint iqmp. Total 16 +
567 bloblen
= 16 + dlen
+ plen
+ qlen
+ ulen
;
568 blob
= snewn(bloblen
, unsigned char);
573 *p
++ = bignum_byte(rsa
->private_exponent
, i
);
577 *p
++ = bignum_byte(rsa
->p
, i
);
581 *p
++ = bignum_byte(rsa
->q
, i
);
585 *p
++ = bignum_byte(rsa
->iqmp
, i
);
586 assert(p
== blob
+ bloblen
);
591 static void *rsa2_createkey(unsigned char *pub_blob
, int pub_len
,
592 unsigned char *priv_blob
, int priv_len
)
595 char *pb
= (char *) priv_blob
;
597 rsa
= rsa2_newkey((char *) pub_blob
, pub_len
);
598 rsa
->private_exponent
= getmp(&pb
, &priv_len
);
599 rsa
->p
= getmp(&pb
, &priv_len
);
600 rsa
->q
= getmp(&pb
, &priv_len
);
601 rsa
->iqmp
= getmp(&pb
, &priv_len
);
603 if (!rsa_verify(rsa
)) {
611 static void *rsa2_openssh_createkey(unsigned char **blob
, int *len
)
613 char **b
= (char **) blob
;
616 rsa
= snew(struct RSAKey
);
621 rsa
->modulus
= getmp(b
, len
);
622 rsa
->exponent
= getmp(b
, len
);
623 rsa
->private_exponent
= getmp(b
, len
);
624 rsa
->iqmp
= getmp(b
, len
);
625 rsa
->p
= getmp(b
, len
);
626 rsa
->q
= getmp(b
, len
);
628 if (!rsa
->modulus
|| !rsa
->exponent
|| !rsa
->private_exponent
||
629 !rsa
->iqmp
|| !rsa
->p
|| !rsa
->q
) {
631 sfree(rsa
->exponent
);
632 sfree(rsa
->private_exponent
);
643 static int rsa2_openssh_fmtkey(void *key
, unsigned char *blob
, int len
)
645 struct RSAKey
*rsa
= (struct RSAKey
*) key
;
649 ssh2_bignum_length(rsa
->modulus
) +
650 ssh2_bignum_length(rsa
->exponent
) +
651 ssh2_bignum_length(rsa
->private_exponent
) +
652 ssh2_bignum_length(rsa
->iqmp
) +
653 ssh2_bignum_length(rsa
->p
) + ssh2_bignum_length(rsa
->q
);
660 PUT_32BIT(blob+bloblen, ssh2_bignum_length((x))-4); bloblen += 4; \
661 for (i = ssh2_bignum_length((x))-4; i-- ;) blob[bloblen++]=bignum_byte((x),i);
664 ENC(rsa
->private_exponent
);
672 static int rsa2_pubkey_bits(void *blob
, int len
)
677 rsa
= rsa2_newkey((char *) blob
, len
);
678 ret
= bignum_bitcount(rsa
->modulus
);
684 static char *rsa2_fingerprint(void *key
)
686 struct RSAKey
*rsa
= (struct RSAKey
*) key
;
687 struct MD5Context md5c
;
688 unsigned char digest
[16], lenbuf
[4];
689 char buffer
[16 * 3 + 40];
694 MD5Update(&md5c
, (unsigned char *)"\0\0\0\7ssh-rsa", 11);
696 #define ADD_BIGNUM(bignum) \
697 numlen = (bignum_bitcount(bignum)+8)/8; \
698 PUT_32BIT(lenbuf, numlen); MD5Update(&md5c, lenbuf, 4); \
699 for (i = numlen; i-- ;) { \
700 unsigned char c = bignum_byte(bignum, i); \
701 MD5Update(&md5c, &c, 1); \
703 ADD_BIGNUM(rsa
->exponent
);
704 ADD_BIGNUM(rsa
->modulus
);
707 MD5Final(digest
, &md5c
);
709 sprintf(buffer
, "ssh-rsa %d ", bignum_bitcount(rsa
->modulus
));
710 for (i
= 0; i
< 16; i
++)
711 sprintf(buffer
+ strlen(buffer
), "%s%02x", i ?
":" : "",
713 ret
= snewn(strlen(buffer
) + 1, char);
720 * This is the magic ASN.1/DER prefix that goes in the decoded
721 * signature, between the string of FFs and the actual SHA hash
722 * value. The meaning of it is:
724 * 00 -- this marks the end of the FFs; not part of the ASN.1 bit itself
726 * 30 21 -- a constructed SEQUENCE of length 0x21
727 * 30 09 -- a constructed sub-SEQUENCE of length 9
728 * 06 05 -- an object identifier, length 5
729 * 2B 0E 03 02 1A -- object id { 1 3 14 3 2 26 }
730 * (the 1,3 comes from 0x2B = 43 = 40*1+3)
732 * 04 14 -- a primitive OCTET STRING of length 0x14
733 * [0x14 bytes of hash data follows]
735 * The object id in the middle there is listed as `id-sha1' in
736 * ftp://ftp.rsasecurity.com/pub/pkcs/pkcs-1/pkcs-1v2-1d2.asn (the
737 * ASN module for PKCS #1) and its expanded form is as follows:
739 * id-sha1 OBJECT IDENTIFIER ::= {
740 * iso(1) identified-organization(3) oiw(14) secsig(3)
743 static const unsigned char asn1_weird_stuff
[] = {
744 0x00, 0x30, 0x21, 0x30, 0x09, 0x06, 0x05, 0x2B,
745 0x0E, 0x03, 0x02, 0x1A, 0x05, 0x00, 0x04, 0x14,
748 #define ASN1_LEN ( (int) sizeof(asn1_weird_stuff) )
750 static int rsa2_verifysig(void *key
, char *sig
, int siglen
,
751 char *data
, int datalen
)
753 struct RSAKey
*rsa
= (struct RSAKey
*) key
;
757 int bytes
, i
, j
, ret
;
758 unsigned char hash
[20];
760 getstring(&sig
, &siglen
, &p
, &slen
);
761 if (!p
|| slen
!= 7 || memcmp(p
, "ssh-rsa", 7)) {
764 in
= getmp(&sig
, &siglen
);
765 out
= modpow(in
, rsa
->exponent
, rsa
->modulus
);
770 bytes
= (bignum_bitcount(rsa
->modulus
)+7) / 8;
771 /* Top (partial) byte should be zero. */
772 if (bignum_byte(out
, bytes
- 1) != 0)
774 /* First whole byte should be 1. */
775 if (bignum_byte(out
, bytes
- 2) != 1)
777 /* Most of the rest should be FF. */
778 for (i
= bytes
- 3; i
>= 20 + ASN1_LEN
; i
--) {
779 if (bignum_byte(out
, i
) != 0xFF)
782 /* Then we expect to see the asn1_weird_stuff. */
783 for (i
= 20 + ASN1_LEN
- 1, j
= 0; i
>= 20; i
--, j
++) {
784 if (bignum_byte(out
, i
) != asn1_weird_stuff
[j
])
787 /* Finally, we expect to see the SHA-1 hash of the signed data. */
788 SHA_Simple(data
, datalen
, hash
);
789 for (i
= 19, j
= 0; i
>= 0; i
--, j
++) {
790 if (bignum_byte(out
, i
) != hash
[j
])
798 static unsigned char *rsa2_sign(void *key
, char *data
, int datalen
,
801 struct RSAKey
*rsa
= (struct RSAKey
*) key
;
802 unsigned char *bytes
;
804 unsigned char hash
[20];
808 SHA_Simple(data
, datalen
, hash
);
810 nbytes
= (bignum_bitcount(rsa
->modulus
) - 1) / 8;
811 assert(1 <= nbytes
- 20 - ASN1_LEN
);
812 bytes
= snewn(nbytes
, unsigned char);
815 for (i
= 1; i
< nbytes
- 20 - ASN1_LEN
; i
++)
817 for (i
= nbytes
- 20 - ASN1_LEN
, j
= 0; i
< nbytes
- 20; i
++, j
++)
818 bytes
[i
] = asn1_weird_stuff
[j
];
819 for (i
= nbytes
- 20, j
= 0; i
< nbytes
; i
++, j
++)
822 in
= bignum_from_bytes(bytes
, nbytes
);
825 out
= rsa_privkey_op(in
, rsa
);
828 nbytes
= (bignum_bitcount(out
) + 7) / 8;
829 bytes
= snewn(4 + 7 + 4 + nbytes
, unsigned char);
831 memcpy(bytes
+ 4, "ssh-rsa", 7);
832 PUT_32BIT(bytes
+ 4 + 7, nbytes
);
833 for (i
= 0; i
< nbytes
; i
++)
834 bytes
[4 + 7 + 4 + i
] = bignum_byte(out
, nbytes
- 1 - i
);
837 *siglen
= 4 + 7 + 4 + nbytes
;
841 const struct ssh_signkey ssh_rsa
= {
848 rsa2_openssh_createkey
,
858 void *ssh_rsakex_newkey(char *data
, int len
)
860 return rsa2_newkey(data
, len
);
863 void ssh_rsakex_freekey(void *key
)
868 int ssh_rsakex_klen(void *key
)
870 struct RSAKey
*rsa
= (struct RSAKey
*) key
;
872 return bignum_bitcount(rsa
->modulus
);
875 static void oaep_mask(const struct ssh_hash
*h
, void *seed
, int seedlen
,
876 void *vdata
, int datalen
)
878 unsigned char *data
= (unsigned char *)vdata
;
881 while (datalen
> 0) {
882 int i
, max
= (datalen
> h
->hlen ? h
->hlen
: datalen
);
884 unsigned char counter
[4], hash
[SSH2_KEX_MAX_HASH_LEN
];
886 assert(h
->hlen
<= SSH2_KEX_MAX_HASH_LEN
);
887 PUT_32BIT(counter
, count
);
889 h
->bytes(s
, seed
, seedlen
);
890 h
->bytes(s
, counter
, 4);
894 for (i
= 0; i
< max
; i
++)
902 void ssh_rsakex_encrypt(const struct ssh_hash
*h
, unsigned char *in
, int inlen
,
903 unsigned char *out
, int outlen
,
907 struct RSAKey
*rsa
= (struct RSAKey
*) key
;
910 const int HLEN
= h
->hlen
;
913 * Here we encrypt using RSAES-OAEP. Essentially this means:
915 * - we have a SHA-based `mask generation function' which
916 * creates a pseudo-random stream of mask data
917 * deterministically from an input chunk of data.
919 * - we have a random chunk of data called a seed.
921 * - we use the seed to generate a mask which we XOR with our
924 * - then we use _the masked plaintext_ to generate a mask
925 * which we XOR with the seed.
927 * - then we concatenate the masked seed and the masked
928 * plaintext, and RSA-encrypt that lot.
930 * The result is that the data input to the encryption function
931 * is random-looking and (hopefully) contains no exploitable
932 * structure such as PKCS1-v1_5 does.
934 * For a precise specification, see RFC 3447, section 7.1.1.
935 * Some of the variable names below are derived from that, so
936 * it'd probably help to read it anyway.
939 /* k denotes the length in octets of the RSA modulus. */
940 k
= (7 + bignum_bitcount(rsa
->modulus
)) / 8;
942 /* The length of the input data must be at most k - 2hLen - 2. */
943 assert(inlen
> 0 && inlen
<= k
- 2*HLEN
- 2);
945 /* The length of the output data wants to be precisely k. */
949 * Now perform EME-OAEP encoding. First set up all the unmasked
952 /* Leading byte zero. */
954 /* At position 1, the seed: HLEN bytes of random data. */
955 for (i
= 0; i
< HLEN
; i
++)
956 out
[i
+ 1] = random_byte();
957 /* At position 1+HLEN, the data block DB, consisting of: */
958 /* The hash of the label (we only support an empty label here) */
959 h
->final(h
->init(), out
+ HLEN
+ 1);
960 /* A bunch of zero octets */
961 memset(out
+ 2*HLEN
+ 1, 0, outlen
- (2*HLEN
+ 1));
962 /* A single 1 octet, followed by the input message data. */
963 out
[outlen
- inlen
- 1] = 1;
964 memcpy(out
+ outlen
- inlen
, in
, inlen
);
967 * Now use the seed data to mask the block DB.
969 oaep_mask(h
, out
+1, HLEN
, out
+HLEN
+1, outlen
-HLEN
-1);
972 * And now use the masked DB to mask the seed itself.
974 oaep_mask(h
, out
+HLEN
+1, outlen
-HLEN
-1, out
+1, HLEN
);
977 * Now `out' contains precisely the data we want to
980 b1
= bignum_from_bytes(out
, outlen
);
981 b2
= modpow(b1
, rsa
->exponent
, rsa
->modulus
);
983 for (i
= outlen
; i
--;) {
984 *p
++ = bignum_byte(b2
, i
);
994 static const struct ssh_kex ssh_rsa_kex_sha1
= {
995 "rsa1024-sha1", NULL
, KEXTYPE_RSA
, NULL
, NULL
, 0, 0, &ssh_sha1
998 static const struct ssh_kex ssh_rsa_kex_sha256
= {
999 "rsa2048-sha256", NULL
, KEXTYPE_RSA
, NULL
, NULL
, 0, 0, &ssh_sha256
1002 static const struct ssh_kex
*const rsa_kex_list
[] = {
1003 &ssh_rsa_kex_sha256
,
1007 const struct ssh_kexes ssh_rsa_kex
= {
1008 sizeof(rsa_kex_list
) / sizeof(*rsa_kex_list
),