crypto: rng - RNG interface and implementation
This patch adds a random number generator interface as well as a
cryptographic pseudo-random number generator based on AES. It is
meant to be used in cases where a deterministic CPRNG is required.
One of the first applications will be as an input in the IPsec IV
generation process.
Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
diff --git a/crypto/ansi_cprng.c b/crypto/ansi_cprng.c
new file mode 100644
index 0000000..72db0fd
--- /dev/null
+++ b/crypto/ansi_cprng.c
@@ -0,0 +1,417 @@
+/*
+ * PRNG: Pseudo Random Number Generator
+ * Based on NIST Recommended PRNG From ANSI X9.31 Appendix A.2.4 using
+ * AES 128 cipher
+ *
+ * (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 <crypto/internal/rng.h>
+#include <linux/err.h>
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/moduleparam.h>
+#include <linux/string.h>
+
+#include "internal.h"
+
+#define DEFAULT_PRNG_KEY "0123456789abcdef"
+#define DEFAULT_PRNG_KSZ 16
+#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 {
+ 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_cipher *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;
+ unsigned char tmp[DEFAULT_BLK_SZ];
+ unsigned char *output = NULL;
+
+
+ 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++) {
+
+ switch (i) {
+ case 0:
+ /*
+ * Start by encrypting the counter value
+ * This gives us an intermediate value I
+ */
+ memcpy(tmp, ctx->DT, DEFAULT_BLK_SZ);
+ output = ctx->I;
+ 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);
+ hexdump("tmp stage 1: ", tmp, DEFAULT_BLK_SZ);
+ output = ctx->rand_data;
+ 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 -EINVAL;
+ }
+ 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);
+ output = ctx->V;
+ hexdump("tmp stage 2: ", tmp, DEFAULT_BLK_SZ);
+ break;
+ }
+
+
+ /* do the encryption */
+ crypto_cipher_encrypt_one(ctx->tfm, output, tmp);
+
+ }
+
+ /*
+ * Now update our DT value
+ */
+ for (i = 0; i < DEFAULT_BLK_SZ; i++) {
+ ctx->DT[i] += 1;
+ if (ctx->DT[i] != 0)
+ break;
+ }
+
+ 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 */
+static int get_prng_bytes(char *buf, size_t 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 = -EINVAL;
+ 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 = -EINVAL;
+ 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 = -EINVAL;
+ 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;
+}
+
+static void free_prng_context(struct prng_context *ctx)
+{
+ crypto_free_cipher(ctx->tfm);
+}
+
+static int reset_prng_context(struct prng_context *ctx,
+ unsigned char *key, size_t klen,
+ unsigned char *V, unsigned char *DT)
+{
+ int ret;
+ int rc = -EINVAL;
+ unsigned char *prng_key;
+
+ spin_lock(&ctx->prng_lock);
+ ctx->flags |= PRNG_NEED_RESET;
+
+ prng_key = (key != NULL) ? key : (unsigned char *)DEFAULT_PRNG_KEY;
+
+ if (!key)
+ klen = DEFAULT_PRNG_KSZ;
+
+ 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_cipher(ctx->tfm);
+
+ ctx->tfm = crypto_alloc_cipher("aes", 0, 0);
+ if (IS_ERR(ctx->tfm)) {
+ dbgprint(KERN_CRIT "Failed to alloc tfm for context %p\n",
+ ctx);
+ ctx->tfm = NULL;
+ goto out;
+ }
+
+ ctx->rand_data_valid = DEFAULT_BLK_SZ;
+
+ ret = crypto_cipher_setkey(ctx->tfm, prng_key, klen);
+ if (ret) {
+ dbgprint(KERN_CRIT "PRNG: setkey() failed flags=%x\n",
+ crypto_cipher_get_flags(ctx->tfm));
+ crypto_free_cipher(ctx->tfm);
+ goto out;
+ }
+
+ rc = 0;
+ ctx->flags &= ~PRNG_NEED_RESET;
+out:
+ spin_unlock(&ctx->prng_lock);
+
+ return rc;
+
+}
+
+static int cprng_init(struct crypto_tfm *tfm)
+{
+ struct prng_context *ctx = crypto_tfm_ctx(tfm);
+
+ spin_lock_init(&ctx->prng_lock);
+
+ return reset_prng_context(ctx, NULL, DEFAULT_PRNG_KSZ, NULL, NULL);
+}
+
+static void cprng_exit(struct crypto_tfm *tfm)
+{
+ free_prng_context(crypto_tfm_ctx(tfm));
+}
+
+static int cprng_get_random(struct crypto_rng *tfm, u8 *rdata,
+ unsigned int dlen)
+{
+ struct prng_context *prng = crypto_rng_ctx(tfm);
+
+ return get_prng_bytes(rdata, dlen, prng);
+}
+
+static int cprng_reset(struct crypto_rng *tfm, u8 *seed, unsigned int slen)
+{
+ struct prng_context *prng = crypto_rng_ctx(tfm);
+ u8 *key = seed + DEFAULT_PRNG_KSZ;
+
+ if (slen < DEFAULT_PRNG_KSZ + DEFAULT_BLK_SZ)
+ return -EINVAL;
+
+ reset_prng_context(prng, key, DEFAULT_PRNG_KSZ, seed, NULL);
+
+ if (prng->flags & PRNG_NEED_RESET)
+ return -EINVAL;
+ return 0;
+}
+
+static struct crypto_alg rng_alg = {
+ .cra_name = "stdrng",
+ .cra_driver_name = "ansi_cprng",
+ .cra_priority = 100,
+ .cra_flags = CRYPTO_ALG_TYPE_RNG,
+ .cra_ctxsize = sizeof(struct prng_context),
+ .cra_type = &crypto_rng_type,
+ .cra_module = THIS_MODULE,
+ .cra_list = LIST_HEAD_INIT(rng_alg.cra_list),
+ .cra_init = cprng_init,
+ .cra_exit = cprng_exit,
+ .cra_u = {
+ .rng = {
+ .rng_make_random = cprng_get_random,
+ .rng_reset = cprng_reset,
+ .seedsize = DEFAULT_PRNG_KSZ + DEFAULT_BLK_SZ,
+ }
+ }
+};
+
+
+/* Module initalization */
+static int __init prng_mod_init(void)
+{
+ int ret = 0;
+
+ if (fips_enabled)
+ rng_alg.cra_priority += 200;
+
+ ret = crypto_register_alg(&rng_alg);
+
+ if (ret)
+ goto out;
+out:
+ return 0;
+}
+
+static void __exit prng_mod_fini(void)
+{
+ crypto_unregister_alg(&rng_alg);
+ 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);
+MODULE_ALIAS("stdrng");
