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New API for primegen(), using PrimeCandidateSource.

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The more features and options I add to PrimeCandidateSource, the more
cumbersome it will be to replicate each one in a command-line option
to the ultimate primegen() function. So I'm moving to an API in which
the client of primegen() constructs a PrimeCandidateSource themself,
and passes it in to primegen().

Also, changed the API for pcs_new() so that you don't have to pass
'firstbits' unless you really want to. The net effect is that even
though we've added flexibility, we've also simplified the call sites
of primegen() in the simple case: if you want a 1234-bit prime, you
just need to pass pcs_new(1234) as the argument to primegen, and
you're done.

The new declaration of primegen() lives in ssh_keygen.h, along with
all the types it depends on. So I've had to #include that header in a
few new files.
This commit is contained in:
Simon Tatham
2020-02-24 19:09:08 +00:00
parent 809a4eb249
commit 63b8f537f2
11 changed files with 64 additions and 58 deletions
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39
sshprime.c
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@ -108,44 +108,13 @@
* all, so after we've seen a -1 we can be sure of seeing nothing
* but 1s.)
*/
/*
* 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.
*
* - for the basically cosmetic purposes of generating keys of the
* length actually specified rather than off by one bit, we permit
* the caller to provide an unsigned integer 'firstbits' which will
* match the top few bits of the returned prime. (That is, there
* will exist some n such that (returnvalue >> n) == firstbits.) If
* 'firstbits' is not needed, specifying it to either 0 or 1 is
* an adequate no-op.
*/
mp_int *primegen(
int bits, int modulus, int residue, mp_int *factor,
int phase, progfn_t pfn, void *pfnparam, unsigned firstbits)
mp_int *primegen(PrimeCandidateSource *pcs,
int phase, progfn_t pfn, void *pfnparam)
{
int progress = 0;
size_t fbsize = 0;
while (firstbits >> fbsize) /* work out how to align this */
fbsize++;
PrimeCandidateSource *pcs = pcs_new(bits, firstbits, fbsize);
if (factor)
pcs_require_residue_1(pcs, factor);
if (modulus)
pcs_avoid_residue_small(pcs, modulus, residue);
pcs_ready(pcs);
int progress = 0;
STARTOVER:
pfn(pfnparam, PROGFN_PROGRESS, phase, ++progress);