crypto: prng - Deterministic CPRNG

This patch adds a cryptographic pseudo-random number generator
based on CTR(AES-128).  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>

crypto/Kconfig

@@ -666,6 +666,15 @@ config CRYPTO_LZO
 	help
 	  This is the LZO algorithm.
 
+comment "Random Number Generation"
+
+config CRYPTO_PRNG
+	tristate "Pseudo Random Number Generation for Cryptographic modules"
+	help
+	  This option enables the generic pseudo random number generator
+	  for cryptographic modules.  Uses the Algorithm specified in
+	  ANSI X9.31 A.2.4
+
 source "drivers/crypto/Kconfig"
 
 endif	# if CRYPTO

crypto/Makefile

@@ -69,7 +69,7 @@ obj-$(CONFIG_CRYPTO_MICHAEL_MIC) += michael_mic.o
 obj-$(CONFIG_CRYPTO_CRC32C) += crc32c.o
 obj-$(CONFIG_CRYPTO_AUTHENC) += authenc.o
 obj-$(CONFIG_CRYPTO_LZO) += lzo.o
-
+obj-$(CONFIG_CRYPTO_PRNG) += prng.o
 obj-$(CONFIG_CRYPTO_TEST) += tcrypt.o
 
 #

crypto/prng.c

+/*
+ * 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);

crypto/prng.h

+/*
+ * PRNG: Pseudo Random Number Generator
+ *
+ *  (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.
+ *
+ *
+ */
+
+#ifndef _PRNG_H_
+#define _PRNG_H_
+struct prng_context;
+
+int get_prng_bytes(char *buf, int nbytes, struct prng_context *ctx);
+struct prng_context *alloc_prng_context(void);
+int reset_prng_context(struct prng_context *ctx,
+			unsigned char *key, unsigned char *iv,
+			unsigned char *V,
+			unsigned char *DT);
+void free_prng_context(struct prng_context *ctx);
+
+#endif
+