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>

1 files changed, 417 insertions, 0 deletions

diff --git a/crypto/ansi_cprng.c b/crypto/ansi_cprng.c
new file mode 100644
index 00000000000..72db0fd763c
--- /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");