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Add support for using Diffie-Hellman with short exponents (sshdh.c

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contains a reference to a paper on the subject). Reduces time taken
for DH group exchange to the point where it's viable to enable it
all the time, so I have. :-)

[originally from svn r991]
This commit is contained in:
Simon Tatham
2001-03-10 11:04:07 +00:00
parent 0c8635beda
commit d823077f18
3 changed files with 59 additions and 29 deletions
Download Patch File Download Diff File Expand all files Collapse all files

46
ssh.c
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@ -179,9 +179,7 @@ const static struct ssh2_ciphers *ciphers[] = {
};
const static struct ssh_kex *kex_algs[] = {
#ifdef DO_DIFFIE_HELLMAN_GEX
&ssh_diffiehellman_gex,
#endif
&ssh_diffiehellman };
const static struct ssh_signkey *hostkey_algs[] = { &ssh_rsa, &ssh_dss };
@ -2331,7 +2329,7 @@ static void ssh2_mkkey(Bignum K, char *H, char *sessid, char chr, char *keyspace
*/
static int do_ssh2_transport(unsigned char *in, int inlen, int ispkt)
{
static int i, j, len, nbits;
static int i, j, len, nbits, pbits;
static char *str;
static Bignum p, g, e, f, K;
static int kex_init_value, kex_reply_value;
@ -2553,31 +2551,35 @@ static int do_ssh2_transport(unsigned char *in, int inlen, int ispkt)
}
}
/*
* Work out the number of bits of key we will need from the key
* exchange. We start with the maximum key length of either
* cipher...
*/
{
int csbits, scbits;
csbits = cscipher_tobe->keylen;
scbits = sccipher_tobe->keylen;
nbits = (csbits > scbits ? csbits : scbits);
}
/* The keys only have 160-bit entropy, since they're based on
* a SHA-1 hash. So cap the key size at 160 bits. */
if (nbits > 160) nbits = 160;
/*
* If we're doing Diffie-Hellman group exchange, start by
* requesting a group.
*/
if (kex == &ssh_diffiehellman_gex) {
int csbits, scbits;
logevent("Doing Diffie-Hellman group exchange");
/*
* Work out number of bits. We start with the maximum key
* length of either cipher...
*/
csbits = cscipher_tobe->keylen;
scbits = sccipher_tobe->keylen;
nbits = (csbits > scbits ? csbits : scbits);
/* The keys only have 160-bit entropy, since they're based on
* a SHA-1 hash. So cap the key size at 160 bits. */
if (nbits > 160) nbits = 160;
/*
* ... and then work out how big a DH group we will need to
* allow that much data.
*/
nbits = 512 << ((nbits-1) / 64);
* Work out how big a DH group we will need to allow that
* much data.
*/
pbits = 512 << ((nbits-1) / 64);
ssh2_pkt_init(SSH2_MSG_KEX_DH_GEX_REQUEST);
ssh2_pkt_adduint32(nbits);
ssh2_pkt_adduint32(pbits);
ssh2_pkt_send();
crWaitUntil(ispkt);
@ -2600,7 +2602,7 @@ static int do_ssh2_transport(unsigned char *in, int inlen, int ispkt)
/*
* Now generate and send e for Diffie-Hellman.
*/
e = dh_create_e();
e = dh_create_e(nbits*2);
ssh2_pkt_init(kex_init_value);
ssh2_pkt_addmp(e);
ssh2_pkt_send();
@ -2618,7 +2620,7 @@ static int do_ssh2_transport(unsigned char *in, int inlen, int ispkt)
sha_string(&exhash, hostkeydata, hostkeylen);
if (kex == &ssh_diffiehellman_gex) {
sha_uint32(&exhash, nbits);
sha_uint32(&exhash, pbits);
sha_mpint(&exhash, p);
sha_mpint(&exhash, g);
}