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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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20
import.c
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@ -988,7 +988,7 @@ static bool openssh_pem_write(
*/
if (passphrase) {
unsigned char keybuf[32];
int origlen, outlen, pad, i;
int origlen, outlen, pad;
/*
* Padding on OpenSSH keys is deterministic. The number of
@ -1015,7 +1015,7 @@ static bool openssh_pem_write(
/*
* Invent an iv, and derive the encryption key.
*/
for (i = 0; i < 8; i++) iv[i] = random_byte();
random_read(iv, 8);
openssh_pem_derivekey(ptrlen_from_asciz(passphrase), iv, keybuf);
@ -1498,7 +1498,7 @@ static bool openssh_new_write(
const Filename *filename, ssh2_userkey *key, const char *passphrase)
{
strbuf *pubblob, *privblob, *cblob;
int padvalue, i;
int padvalue;
unsigned checkint;
bool ret = false;
unsigned char bcrypt_salt[16];
@ -1530,8 +1530,7 @@ static bool openssh_new_write(
} else {
strbuf *substr;
for (i = 0; i < (int)sizeof(bcrypt_salt); i++)
bcrypt_salt[i] = random_byte();
random_read(bcrypt_salt, sizeof(bcrypt_salt));
put_stringz(cblob, "aes256-ctr");
put_stringz(cblob, "bcrypt");
substr = strbuf_new();
@ -1551,9 +1550,9 @@ static bool openssh_new_write(
strbuf *cpblob = strbuf_new();
/* checkint. */
checkint = 0;
for (i = 0; i < 4; i++)
checkint = (checkint << 8) + random_byte();
uint8_t checkint_buf[4];
random_read(checkint_buf, 4);
checkint = GET_32BIT_MSB_FIRST(checkint_buf);
put_uint32(cpblob, checkint);
put_uint32(cpblob, checkint);
@ -2279,8 +2278,9 @@ static bool sshcom_write(
/* Pad encrypted blob to a multiple of cipher block size. */
if (passphrase) {
int padding = -(outblob->len - (lenpos+4)) & 7;
while (padding--)
put_byte(outblob, random_byte());
uint8_t padding_buf[8];
random_read(padding_buf, padding);
put_data(outblob, padding_buf, padding);
}
ciphertext = outblob->s + lenpos + 4;
cipherlen = outblob->len - (lenpos + 4);