/*
* PRNG: Pseudo Random Number Generator
* Based on NIST Recommended PRNG From ANSI X9.31 Appendix A.2.4 using
* AES 128 cipher in RFC3686 ctr mode
*
* (C) Neil Horman <nhorman@tuxdriver.com>
*
* This program is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License as published by the
* Free Software Foundation; either version 2 of the License, or (at your
* any later version.
*
*
*/
#include <linux/err.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/mm.h>
#include <linux/slab.h>
#include <linux/fs.h>
#include <linux/scatterlist.h>
#include <linux/string.h>
#include <linux/crypto.h>
#include <linux/highmem.h>
#include <linux/moduleparam.h>
#include <linux/jiffies.h>
#include <linux/timex.h>
#include <linux/interrupt.h>
#include <linux/miscdevice.h>
#include "prng.h"
#define TEST_PRNG_ON_START 0
#define DEFAULT_PRNG_KEY "0123456789abcdef1011"
#define DEFAULT_PRNG_KSZ 20
#define DEFAULT_PRNG_IV "defaultv"
#define DEFAULT_PRNG_IVSZ 8
#define DEFAULT_BLK_SZ 16
#define DEFAULT_V_SEED "zaybxcwdveuftgsh"
/*
* Flags for the prng_context flags field
*/
#define PRNG_FIXED_SIZE 0x1
#define PRNG_NEED_RESET 0x2
/*
* Note: DT is our counter value
* I is our intermediate value
* V is our seed vector
* See http://csrc.nist.gov/groups/STM/cavp/documents/rng/931rngext.pdf
* for implementation details
*/
struct prng_context {
char *prng_key;
char *prng_iv;
spinlock_t prng_lock;
unsigned char rand_data[DEFAULT_BLK_SZ];
unsigned char last_rand_data[DEFAULT_BLK_SZ];
unsigned char DT[DEFAULT_BLK_SZ];
unsigned char I[DEFAULT_BLK_SZ];
unsigned char V[DEFAULT_BLK_SZ];
u32 rand_data_valid;
struct crypto_blkcipher *tfm;
u32 flags;
};
static int dbg;
static void hexdump(char *note, unsigned char *buf, unsigned int len)
{
if (dbg) {
printk(KERN_CRIT "%s", note);
print_hex_dump(KERN_CONT, "", DUMP_PREFIX_OFFSET,
16, 1,
buf, len, false);
}
}
#define dbgprint(format, args...) do {if(dbg) printk(format, ##args);} while(0)
static void xor_vectors(unsigned char *in1, unsigned char *in2,
unsigned char *out, unsigned int size)
{
int i;
for (i=0;i<size;i++)
out[i] = in1[i] ^ in2[i];
}
/*
* Returns DEFAULT_BLK_SZ bytes of random data per call
* returns 0 if generation succeded, <0 if something went wrong
*/
static int _get_more_prng_bytes(struct prng_context *ctx)
{
int i;
struct blkcipher_desc desc;
struct scatterlist sg_in, sg_out;
int ret;
unsigned char tmp[DEFAULT_BLK_SZ];
desc.tfm = ctx->tfm;
desc.flags = 0;
dbgprint(KERN_CRIT "Calling _get_more_prng_bytes for context %p\n",ctx);
hexdump("Input DT: ", ctx->DT, DEFAULT_BLK_SZ);
hexdump("Input I: ", ctx->I, DEFAULT_BLK_SZ);
hexdump("Input V: ", ctx->V, DEFAULT_BLK_SZ);
/*
* This algorithm is a 3 stage state machine
*/
for (i=0;i<3;i++) {
desc.tfm = ctx->tfm;
desc.flags = 0;
switch (i) {
case 0:
/*
* Start by encrypting the counter value
* This gives us an intermediate value I
*/
memcpy(tmp, ctx->DT, DEFAULT_BLK_SZ);
sg_init_one(&sg_out, &ctx->I[0], DEFAULT_BLK_SZ);
hexdump("tmp stage 0: ", tmp, DEFAULT_BLK_SZ);
break;
case 1:
/*
* Next xor I with our secret vector V
* encrypt that result to obtain our
* pseudo random data which we output
*/
xor_vectors(ctx->I, ctx->V, tmp, DEFAULT_BLK_SZ);
sg_init_one(&sg_out, &ctx->rand_data[0], DEFAULT_BLK_SZ);
hexdump("tmp stage 1: ", tmp, DEFAULT_BLK_SZ);
break;
case 2:
/*
* First check that we didn't produce the same random data
* that we did last time around through this
*/
if (!memcmp(ctx->rand_data, ctx->last_rand_data, DEFAULT_BLK_SZ)) {
printk(KERN_ERR "ctx %p Failed repetition check!\n",
ctx);
ctx->flags |= PRNG_NEED_RESET;
return -1;
}
memcpy(ctx->last_rand_data, ctx->rand_data, DEFAULT_BLK_SZ);
/*
* Lastly xor the random data with I
* and encrypt that to obtain a new secret vector V
*/
xor_vectors(ctx->rand_data, ctx->I, tmp, DEFAULT_BLK_SZ);
sg_init_one(&sg_out, &ctx->V[0], DEFAULT_BLK_SZ);
hexdump("tmp stage 2: ", tmp, DEFAULT_BLK_SZ);
break;
}
/* Initialize our input buffer */
sg_init_one(&sg_in, &tmp[0], DEFAULT_BLK_SZ);
/* do the encryption */
ret = crypto_blkcipher_encrypt(&desc, &sg_out, &sg_in, DEFAULT_BLK_SZ);
/* And check the result */
if (ret) {
dbgprint(KERN_CRIT "Encryption of new block failed for context %p\n",ctx);
ctx->rand_data_valid = DEFAULT_BLK_SZ;
return -1;
}
}
/*
* Now update our DT value
*/
for (i=DEFAULT_BLK_SZ-1;i>0;i--) {
ctx->DT[i] = ctx->DT[i-1];
}
ctx->DT[0] += 1;
dbgprint("Returning new block for context %p\n",ctx);
ctx->rand_data_valid = 0;
hexdump("Output DT: ", ctx->DT, DEFAULT_BLK_SZ);
hexdump("Output I: ", ctx->I, DEFAULT_BLK_SZ);
hexdump("Output V: ", ctx->V, DEFAULT_BLK_SZ);
hexdump("New Random Data: ", ctx->rand_data, DEFAULT_BLK_SZ);
return 0;
}
/* Our exported functions */
int get_prng_bytes(char *buf, int nbytes, struct prng_context *ctx)
{
unsigned long flags;
unsigned char *ptr = buf;
unsigned int byte_count = (unsigned int)nbytes;
int err;
if (nbytes < 0)
return -EINVAL;
spin_lock_irqsave(&ctx->prng_lock, flags);
err = -EFAULT;
if (ctx->flags & PRNG_NEED_RESET)
goto done;
/*
* If the FIXED_SIZE flag is on, only return whole blocks of
* pseudo random data
*/
err = -EINVAL;
if (ctx->flags & PRNG_FIXED_SIZE) {
if (nbytes < DEFAULT_BLK_SZ)
goto done;
byte_count = DEFAULT_BLK_SZ;
}
err = byte_count;
dbgprint(KERN_CRIT "getting %d random bytes for context %p\n",byte_count, ctx);
remainder:
if (ctx->rand_data_valid == DEFAULT_BLK_SZ) {
if (_get_more_prng_bytes(ctx) < 0) {
memset(buf, 0, nbytes);
err = -EFAULT;
goto done;
}
}
/*
* Copy up to the next whole block size
*/
if (byte_count < DEFAULT_BLK_SZ) {
for (;ctx->rand_data_valid < DEFAULT_BLK_SZ; ctx->rand_data_valid++) {
*ptr = ctx->rand_data[ctx->rand_data_valid];
ptr++;
byte_count--;
if (byte_count == 0)
goto done;
}
}
/*
* Now copy whole blocks
*/
for(;byte_count >= DEFAULT_BLK_SZ; byte_count -= DEFAULT_BLK_SZ) {
if (_get_more_prng_bytes(ctx) < 0) {
memset(buf, 0, nbytes);
err = -1;
goto done;
}
memcpy(ptr, ctx->rand_data, DEFAULT_BLK_SZ);
ctx->rand_data_valid += DEFAULT_BLK_SZ;
ptr += DEFAULT_BLK_SZ;
}
/*
* Now copy any extra partial data
*/
if (byte_count)
goto remainder;
done:
spin_unlock_irqrestore(&ctx->prng_lock, flags);
dbgprint(KERN_CRIT "returning %d from get_prng_bytes in context %p\n",err, ctx);
return err;
}
EXPORT_SYMBOL_GPL(get_prng_bytes);
struct prng_context *alloc_prng_context(void)
{
struct prng_context *ctx=kzalloc(sizeof(struct prng_context), GFP_KERNEL);
spin_lock_init(&ctx->prng_lock);
if (reset_prng_context(ctx, NULL, NULL, NULL, NULL)) {
kfree(ctx);
ctx = NULL;
}
dbgprint(KERN_CRIT "returning context %p\n",ctx);
return ctx;
}
EXPORT_SYMBOL_GPL(alloc_prng_context);
void free_prng_context(struct prng_context *ctx)
{
crypto_free_blkcipher(ctx->tfm);
kfree(ctx);
}
EXPORT_SYMBOL_GPL(free_prng_context);
int reset_prng_context(struct prng_context *ctx,
unsigned char *key, unsigned char *iv,
unsigned char *V, unsigned char *DT)
{
int ret;
int iv_len;
int rc = -EFAULT;
spin_lock(&ctx->prng_lock);
ctx->flags |= PRNG_NEED_RESET;
if (key)
memcpy(ctx->prng_key,key,strlen(ctx->prng_key));
else
ctx->prng_key = DEFAULT_PRNG_KEY;
if (iv)
memcpy(ctx->prng_iv,iv, strlen(ctx->prng_iv));
else
ctx->prng_iv = DEFAULT_PRNG_IV;
if (V)
memcpy(ctx->V,V,DEFAULT_BLK_SZ);
else
memcpy(ctx->V,DEFAULT_V_SEED,DEFAULT_BLK_SZ);
if (DT)
memcpy(ctx->DT, DT, DEFAULT_BLK_SZ);
else
memset(ctx->DT, 0, DEFAULT_BLK_SZ);
memset(ctx->rand_data,0,DEFAULT_BLK_SZ);
memset(ctx->last_rand_data,0,DEFAULT_BLK_SZ);
if (ctx->tfm)
crypto_free_blkcipher(ctx->tfm);
ctx->tfm = crypto_alloc_blkcipher("rfc3686(ctr(aes))",0,0);
if (!ctx->tfm) {
dbgprint(KERN_CRIT "Failed to alloc crypto tfm for context %p\n",ctx->tfm);
goto out;
}
ctx->rand_data_valid = DEFAULT_BLK_SZ;
ret = crypto_blkcipher_setkey(ctx->tfm, ctx->prng_key, strlen(ctx->prng_key));
if (ret) {
dbgprint(KERN_CRIT "PRNG: setkey() failed flags=%x\n",
crypto_blkcipher_get_flags(ctx->tfm));
crypto_free_blkcipher(ctx->tfm);
goto out;
}
iv_len = crypto_blkcipher_ivsize(ctx->tfm);
if (iv_len) {
crypto_blkcipher_set_iv(ctx->tfm, ctx->prng_iv, iv_len);
}
rc = 0;
ctx->flags &= ~PRNG_NEED_RESET;
out:
spin_unlock(&ctx->prng_lock);
return rc;
}
EXPORT_SYMBOL_GPL(reset_prng_context);
/* Module initalization */
static int __init prng_mod_init(void)
{
#ifdef TEST_PRNG_ON_START
int i;
unsigned char tmpbuf[DEFAULT_BLK_SZ];
struct prng_context *ctx = alloc_prng_context();
if (ctx == NULL)
return -EFAULT;
for (i=0;i<16;i++) {
if (get_prng_bytes(tmpbuf, DEFAULT_BLK_SZ, ctx) < 0) {
free_prng_context(ctx);
return -EFAULT;
}
}
free_prng_context(ctx);
#endif
return 0;
}
static void __exit prng_mod_fini(void)
{
return;
}
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("Software Pseudo Random Number Generator");
MODULE_AUTHOR("Neil Horman <nhorman@tuxdriver.com>");
module_param(dbg, int, 0);
MODULE_PARM_DESC(dbg, "Boolean to enable debugging (0/1 == off/on)");
module_init(prng_mod_init);
module_exit(prng_mod_fini);
