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implement a cache for the CSPRNG

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This commit is contained in:
Daniel Micay 2018-08-23 16:30:44 -04:00
parent 70d61b6662
commit daa44905ee
2 changed files with 26 additions and 5 deletions
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24
random.c
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@ -1,4 +1,5 @@
#include <errno.h> #include <errno.h>
#include <string.h>
#include <sys/random.h> #include <sys/random.h>
@ -22,12 +23,27 @@ void get_random_seed(void *buf, size_t size) {
} }
} }
void random_state_init(UNUSED struct random_state *state) { void random_state_init(struct random_state *state) {
state->index = RANDOM_CACHE_SIZE;
} }
// TODO: add ChaCha20-based CSPRNG, for now avoid using this other than during initialization... void get_random_bytes(struct random_state *state, void *buf, size_t size) {
void get_random_bytes(UNUSED struct random_state *state, void *buf, size_t size) { if (size > RANDOM_CACHE_SIZE / 2) {
get_random_seed(buf, size); get_random_seed(buf, size);
return;
}
while (size) {
if (state->index == RANDOM_CACHE_SIZE) {
state->index = 0;
get_random_seed(state->cache, RANDOM_CACHE_SIZE);
}
size_t remaining = RANDOM_CACHE_SIZE - state->index;
size_t copy_size = size < remaining ? size : remaining;
memcpy(buf, state->cache + state->index, copy_size);
state->index += copy_size;
size -= copy_size;
}
} }
size_t get_random_size(struct random_state *state) { size_t get_random_size(struct random_state *state) {

7
random.h
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@ -1,8 +1,13 @@
#ifndef RANDOM_H #ifndef RANDOM_H
#define RANDOM_H #define RANDOM_H
#include <stdint.h>
#define RANDOM_CACHE_SIZE 4096
struct random_state { struct random_state {
char unused; size_t index;
uint8_t cache[RANDOM_CACHE_SIZE];
}; };
void get_random_seed(void *buf, size_t size); void get_random_seed(void *buf, size_t size);