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Add support for DSA authentication in SSH2, following clever ideas

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on how to get round the problem of generating a good k.

[originally from svn r1284]
This commit is contained in:
Simon Tatham
2001-09-22 20:52:21 +00:00
parent 486685c89a
commit d345ebc2a5
11 changed files with 749 additions and 263 deletions
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56
sshprime.c
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@ -2,6 +2,7 @@
* Prime generation.
*/
#include <assert.h>
#include "ssh.h"
/*
@ -1182,14 +1183,25 @@ static const unsigned short primes[] = {
#define NPRIMES (sizeof(primes) / sizeof(*primes))
/*
* Generate a prime. We arrange to select a prime with the property
* (prime % modulus) != residue (to speed up use in RSA).
* Generate a prime. We can deal with various extra properties of
* the prime:
*
* - to speed up use in RSA, we can arrange to select a prime with
* the property (prime % modulus) != residue.
*
* - for use in DSA, we can arrange to select a prime which is one
* more than a multiple of a dirty great bignum. In this case
* `bits' gives the size of the factor by which we _multiply_
* that bignum, rather than the size of the whole number.
*/
Bignum primegen(int bits, int modulus, int residue,
Bignum primegen(int bits, int modulus, int residue, Bignum factor,
int phase, progfn_t pfn, void *pfnparam)
{
int i, k, v, byte, bitsleft, check, checks;
unsigned long delta, moduli[NPRIMES + 1], residues[NPRIMES + 1];
unsigned long delta;
unsigned long moduli[NPRIMES + 1];
unsigned long residues[NPRIMES + 1];
unsigned long multipliers[NPRIMES + 1];
Bignum p, pm1, q, wqp, wqp2;
int progress = 0;
@ -1198,15 +1210,18 @@ Bignum primegen(int bits, int modulus, int residue,
STARTOVER:
pfn(pfnparam, phase, ++progress);
pfn(pfnparam, PROGFN_PROGRESS, phase, ++progress);
/*
* Generate a k-bit random number with top and bottom bits set.
* Alternatively, if `factor' is nonzero, generate a k-bit
* random number with the top bit set and the bottom bit clear,
* multiply it by `factor', and add one.
*/
p = bn_power_2(bits - 1);
for (i = 0; i < bits; i++) {
if (i == 0 || i == bits - 1)
v = 1;
v = (i != 0 || !factor) ? 1 : 0;
else {
if (bitsleft <= 0)
bitsleft = 8, byte = random_byte();
@ -1216,14 +1231,26 @@ Bignum primegen(int bits, int modulus, int residue,
}
bignum_set_bit(p, i, v);
}
if (factor) {
Bignum tmp = p;
p = bigmul(tmp, factor);
freebn(tmp);
assert(bignum_bit(p, 0) == 0);
bignum_set_bit(p, 0, 1);
}
/*
* Ensure this random number is coprime to the first few
* primes, by repeatedly adding 2 to it until it is.
* primes, by repeatedly adding either 2 or 2*factor to it
* until it is.
*/
for (i = 0; i < NPRIMES; i++) {
moduli[i] = primes[i];
residues[i] = bignum_mod_short(p, primes[i]);
if (factor)
multipliers[i] = bignum_mod_short(factor, primes[i]);
else
multipliers[i] = 1;
}
moduli[NPRIMES] = modulus;
residues[NPRIMES] = (bignum_mod_short(p, (unsigned short) modulus)
@ -1231,11 +1258,11 @@ Bignum primegen(int bits, int modulus, int residue,
delta = 0;
while (1) {
for (i = 0; i < (sizeof(moduli) / sizeof(*moduli)); i++)
if (!((residues[i] + delta) % moduli[i]))
if (!((residues[i] + delta * multipliers[i]) % moduli[i]))
break;
if (i < (sizeof(moduli) / sizeof(*moduli))) { /* we broke */
delta += 2;
if (delta < 2) {
if (delta > 65536) {
freebn(p);
goto STARTOVER;
}
@ -1244,7 +1271,14 @@ Bignum primegen(int bits, int modulus, int residue,
break;
}
q = p;
p = bignum_add_long(q, delta);
if (factor) {
Bignum tmp;
tmp = bignum_from_long(delta);
p = bigmuladd(tmp, factor, q);
freebn(tmp);
} else {
p = bignum_add_long(q, delta);
}
freebn(q);
/*
@ -1311,7 +1345,7 @@ Bignum primegen(int bits, int modulus, int residue,
break;
}
pfn(pfnparam, phase, ++progress);
pfn(pfnparam, PROGFN_PROGRESS, phase, ++progress);
/*
* Compute w^q mod p.