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Refactor the ssh_hash vtable. (NFC)

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The idea is to arrange that an ssh_hash object can be reused without
having to free it and allocate a new one. So the 'final' method has
been replaced with 'digest', which does everything except the trailing
free; and there's also a new pair of methods 'reset' and 'copyfrom'
which overwrite the state of a hash with either the starting state or
a copy of another state. Meanwhile, the 'new' allocator function has
stopped performing 'reset' as a side effect; now it _just_ does the
administrative stuff (allocation, setting up vtables), and returns an
object which isn't yet ready to receive any actual data, expecting
that the caller will either reset it or copy another hash state into
it.

In particular, that means that the SHA-384 / SHA-512 pair no longer
need separate 'new' methods, because only the 'reset' part has to
change between them.

This commit makes no change to the user-facing API of wrapper
functions in ssh.h, except to add new functions which nothing yet
calls. The user-facing ssh_hash_new() calls the new and reset methods
in succession, and the copy and final methods still exist to do
new+copy and digest+free.
This commit is contained in:
Simon Tatham
2019-12-15 09:30:10 +00:00
parent 859c81e838
commit 156762fc02
5 changed files with 155 additions and 131 deletions
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26
ssh.h
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@ -715,8 +715,9 @@ struct ssh_hash {
struct ssh_hashalg {
ssh_hash *(*new)(const ssh_hashalg *alg);
ssh_hash *(*copy)(ssh_hash *);
void (*final)(ssh_hash *, unsigned char *); /* ALSO FREES THE ssh_hash! */
void (*reset)(ssh_hash *);
void (*copyfrom)(ssh_hash *dest, ssh_hash *src);
void (*digest)(ssh_hash *, unsigned char *);
void (*free)(ssh_hash *);
int hlen; /* output length in bytes */
int blocklen; /* length of the hash's input block, or 0 for N/A */
@ -726,16 +727,27 @@ struct ssh_hashalg {
};
static inline ssh_hash *ssh_hash_new(const ssh_hashalg *alg)
{ return alg->new(alg); }
static inline ssh_hash *ssh_hash_copy(ssh_hash *h)
{ return h->vt->copy(h); }
static inline void ssh_hash_final(ssh_hash *h, unsigned char *out)
{ h->vt->final(h, out); }
{ ssh_hash *h = alg->new(alg); if (h) h->vt->reset(h); return h; }
static inline ssh_hash *ssh_hash_copy(ssh_hash *orig)
{ ssh_hash *h = orig->vt->new(orig->vt); h->vt->copyfrom(h, orig); return h; }
static inline void ssh_hash_digest(ssh_hash *h, unsigned char *out)
{ h->vt->digest(h, out); }
static inline void ssh_hash_free(ssh_hash *h)
{ h->vt->free(h); }
static inline const ssh_hashalg *ssh_hash_alg(ssh_hash *h)
{ return h->vt; }
/* The reset and copyfrom vtable methods return void. But for call-site
* convenience, these wrappers return their input pointer. */
static inline ssh_hash *ssh_hash_reset(ssh_hash *h)
{ h->vt->reset(h); return h; }
static inline ssh_hash *ssh_hash_copyfrom(ssh_hash *dest, ssh_hash *src)
{ dest->vt->copyfrom(dest, src); return dest; }
/* ssh_hash_final emits the digest _and_ frees the ssh_hash */
static inline void ssh_hash_final(ssh_hash *h, unsigned char *out)
{ h->vt->digest(h, out); h->vt->free(h); }
/* Handy macros for defining all those text-name fields at once */
#define HASHALG_NAMES_BARE(base) \
base, NULL, base