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Replace random_byte() with random_read().

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This is in preparation for a PRNG revamp which will want to have a
well defined boundary for any given request-for-randomness, so that it
can destroy the evidence afterwards. So no more looping round calling
random_byte() and then stopping when we feel like it: now you say up
front how many random bytes you want, and call random_read() which
gives you that many in one go.

Most of the call sites that had to be fixed are fairly mechanical, and
quite a few ended up more concise afterwards. A few became more
cumbersome, such as mp_random_bits, in which the new API doesn't let
me load the random bytes directly into the target integer without
triggering undefined behaviour, so instead I have to allocate a
separate temporary buffer.

The _most_ interesting call site was in the PKCS#1 v1.5 padding code
in sshrsa.c (used in SSH-1), in which you need a stream of _nonzero_
random bytes. The previous code just looped on random_byte, retrying
if it got a zero. Now I'm doing a much more interesting thing with an
mpint, essentially scaling a binary fraction repeatedly to extract a
number in the range [0,255) and then adding 1 to it.
This commit is contained in:
Simon Tatham
2019-01-22 19:43:27 +00:00
parent 76aa3f6f7a
commit 628e794832
21 changed files with 108 additions and 101 deletions
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4
unix/uxsftpserver.c
View File

@ -58,7 +58,6 @@ static int uss_dirhandle_cmp(void *av, void *bv)
static SftpServer *uss_new(const SftpServerVtable *vt)
{
int i;
UnixSftpServer *uss = snew(UnixSftpServer);
memset(uss, 0, sizeof(UnixSftpServer));
@ -66,8 +65,7 @@ static SftpServer *uss_new(const SftpServerVtable *vt)
uss->dirhandles = newtree234(uss_dirhandle_cmp);
uss->srv.vt = vt;
for (i = 0; i < lenof(uss->handlekey); i++)
uss->handlekey[i] = random_byte();
random_read(uss->handlekey, sizeof(uss->handlekey));
return &uss->srv;
}

4
unix/uxshare.c
View File

@ -116,9 +116,7 @@ static char *make_dirname(const char *pi_name, char **logtext)
/*
* Invent some random data.
*/
for (i = 0; i < SALT_SIZE; i++) {
saltbuf[i] = random_byte();
}
random_read(saltbuf, SALT_SIZE);
ret = write(saltfd, saltbuf, SALT_SIZE);
/* POSIX atomicity guarantee: because we wrote less than
* PIPE_BUF bytes, the write either completed in full or