rsa: Split the rsa-verify to separate the modular exponentiation

Public exponentiation which is required in rsa verify functionality is
tightly integrated with verification code in rsa_verify.c. The patch
splits the file into twp separating the modular exponentiation.

1. rsa-verify.c
- The file parses device tree keys node to fill a keyprop structure.
The keyprop structure can then be converted to implementation specific
format.
(struct rsa_pub_key for sw implementation)
- The parsed device tree node is then passed to a generic rsa_mod_exp
function.

2. rsa-mod-exp.c
Move the software specific functions related to modular exponentiation
from rsa-verify.c to this file.

Signed-off-by: Ruchika Gupta <ruchika.gupta@freescale.com>
CC: Simon Glass <sjg@chromium.org>
Acked-by: Simon Glass <sjg@chromium.org>

1 files changed, 303 insertions, 0 deletions

diff --git a/lib/rsa/rsa-mod-exp.c b/lib/rsa/rsa-mod-exp.c
new file mode 100644
index 0000000..4a6de2b
--- /dev/null
+++ b/lib/rsa/rsa-mod-exp.c
@@ -0,0 +1,303 @@
+/*
+ * Copyright (c) 2013, Google Inc.
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#ifndef USE_HOSTCC
+#include <common.h>
+#include <fdtdec.h>
+#include <asm/types.h>
+#include <asm/byteorder.h>
+#include <asm/errno.h>
+#include <asm/types.h>
+#include <asm/unaligned.h>
+#else
+#include "fdt_host.h"
+#include "mkimage.h"
+#include <fdt_support.h>
+#endif
+#include <u-boot/rsa.h>
+#include <u-boot/rsa-mod-exp.h>
+
+#define UINT64_MULT32(v, multby)  (((uint64_t)(v)) * ((uint32_t)(multby)))
+
+#define get_unaligned_be32(a) fdt32_to_cpu(*(uint32_t *)a)
+#define put_unaligned_be32(a, b) (*(uint32_t *)(b) = cpu_to_fdt32(a))
+
+/* Default public exponent for backward compatibility */
+#define RSA_DEFAULT_PUBEXP	65537
+
+/**
+ * subtract_modulus() - subtract modulus from the given value
+ *
+ * @key:	Key containing modulus to subtract
+ * @num:	Number to subtract modulus from, as little endian word array
+ */
+static void subtract_modulus(const struct rsa_public_key *key, uint32_t num[])
+{
+	int64_t acc = 0;
+	uint i;
+
+	for (i = 0; i < key->len; i++) {
+		acc += (uint64_t)num[i] - key->modulus[i];
+		num[i] = (uint32_t)acc;
+		acc >>= 32;
+	}
+}
+
+/**
+ * greater_equal_modulus() - check if a value is >= modulus
+ *
+ * @key:	Key containing modulus to check
+ * @num:	Number to check against modulus, as little endian word array
+ * @return 0 if num < modulus, 1 if num >= modulus
+ */
+static int greater_equal_modulus(const struct rsa_public_key *key,
+				 uint32_t num[])
+{
+	int i;
+
+	for (i = (int)key->len - 1; i >= 0; i--) {
+		if (num[i] < key->modulus[i])
+			return 0;
+		if (num[i] > key->modulus[i])
+			return 1;
+	}
+
+	return 1;  /* equal */
+}
+
+/**
+ * montgomery_mul_add_step() - Perform montgomery multiply-add step
+ *
+ * Operation: montgomery result[] += a * b[] / n0inv % modulus
+ *
+ * @key:	RSA key
+ * @result:	Place to put result, as little endian word array
+ * @a:		Multiplier
+ * @b:		Multiplicand, as little endian word array
+ */
+static void montgomery_mul_add_step(const struct rsa_public_key *key,
+		uint32_t result[], const uint32_t a, const uint32_t b[])
+{
+	uint64_t acc_a, acc_b;
+	uint32_t d0;
+	uint i;
+
+	acc_a = (uint64_t)a * b[0] + result[0];
+	d0 = (uint32_t)acc_a * key->n0inv;
+	acc_b = (uint64_t)d0 * key->modulus[0] + (uint32_t)acc_a;
+	for (i = 1; i < key->len; i++) {
+		acc_a = (acc_a >> 32) + (uint64_t)a * b[i] + result[i];
+		acc_b = (acc_b >> 32) + (uint64_t)d0 * key->modulus[i] +
+				(uint32_t)acc_a;
+		result[i - 1] = (uint32_t)acc_b;
+	}
+
+	acc_a = (acc_a >> 32) + (acc_b >> 32);
+
+	result[i - 1] = (uint32_t)acc_a;
+
+	if (acc_a >> 32)
+		subtract_modulus(key, result);
+}
+
+/**
+ * montgomery_mul() - Perform montgomery mutitply
+ *
+ * Operation: montgomery result[] = a[] * b[] / n0inv % modulus
+ *
+ * @key:	RSA key
+ * @result:	Place to put result, as little endian word array
+ * @a:		Multiplier, as little endian word array
+ * @b:		Multiplicand, as little endian word array
+ */
+static void montgomery_mul(const struct rsa_public_key *key,
+		uint32_t result[], uint32_t a[], const uint32_t b[])
+{
+	uint i;
+
+	for (i = 0; i < key->len; ++i)
+		result[i] = 0;
+	for (i = 0; i < key->len; ++i)
+		montgomery_mul_add_step(key, result, a[i], b);
+}
+
+/**
+ * num_pub_exponent_bits() - Number of bits in the public exponent
+ *
+ * @key:	RSA key
+ * @num_bits:	Storage for the number of public exponent bits
+ */
+static int num_public_exponent_bits(const struct rsa_public_key *key,
+		int *num_bits)
+{
+	uint64_t exponent;
+	int exponent_bits;
+	const uint max_bits = (sizeof(exponent) * 8);
+
+	exponent = key->exponent;
+	exponent_bits = 0;
+
+	if (!exponent) {
+		*num_bits = exponent_bits;
+		return 0;
+	}
+
+	for (exponent_bits = 1; exponent_bits < max_bits + 1; ++exponent_bits)
+		if (!(exponent >>= 1)) {
+			*num_bits = exponent_bits;
+			return 0;
+		}
+
+	return -EINVAL;
+}
+
+/**
+ * is_public_exponent_bit_set() - Check if a bit in the public exponent is set
+ *
+ * @key:	RSA key
+ * @pos:	The bit position to check
+ */
+static int is_public_exponent_bit_set(const struct rsa_public_key *key,
+		int pos)
+{
+	return key->exponent & (1ULL << pos);
+}
+
+/**
+ * pow_mod() - in-place public exponentiation
+ *
+ * @key:	RSA key
+ * @inout:	Big-endian word array containing value and result
+ */
+static int pow_mod(const struct rsa_public_key *key, uint32_t *inout)
+{
+	uint32_t *result, *ptr;
+	uint i;
+	int j, k;
+
+	/* Sanity check for stack size - key->len is in 32-bit words */
+	if (key->len > RSA_MAX_KEY_BITS / 32) {
+		debug("RSA key words %u exceeds maximum %d\n", key->len,
+		      RSA_MAX_KEY_BITS / 32);
+		return -EINVAL;
+	}
+
+	uint32_t val[key->len], acc[key->len], tmp[key->len];
+	uint32_t a_scaled[key->len];
+	result = tmp;  /* Re-use location. */
+
+	/* Convert from big endian byte array to little endian word array. */
+	for (i = 0, ptr = inout + key->len - 1; i < key->len; i++, ptr--)
+		val[i] = get_unaligned_be32(ptr);
+
+	if (0 != num_public_exponent_bits(key, &k))
+		return -EINVAL;
+
+	if (k < 2) {
+		debug("Public exponent is too short (%d bits, minimum 2)\n",
+		      k);
+		return -EINVAL;
+	}
+
+	if (!is_public_exponent_bit_set(key, 0)) {
+		debug("LSB of RSA public exponent must be set.\n");
+		return -EINVAL;
+	}
+
+	/* the bit at e[k-1] is 1 by definition, so start with: C := M */
+	montgomery_mul(key, acc, val, key->rr); /* acc = a * RR / R mod n */
+	/* retain scaled version for intermediate use */
+	memcpy(a_scaled, acc, key->len * sizeof(a_scaled[0]));
+
+	for (j = k - 2; j > 0; --j) {
+		montgomery_mul(key, tmp, acc, acc); /* tmp = acc^2 / R mod n */
+
+		if (is_public_exponent_bit_set(key, j)) {
+			/* acc = tmp * val / R mod n */
+			montgomery_mul(key, acc, tmp, a_scaled);
+		} else {
+			/* e[j] == 0, copy tmp back to acc for next operation */
+			memcpy(acc, tmp, key->len * sizeof(acc[0]));
+		}
+	}
+
+	/* the bit at e[0] is always 1 */
+	montgomery_mul(key, tmp, acc, acc); /* tmp = acc^2 / R mod n */
+	montgomery_mul(key, acc, tmp, val); /* acc = tmp * a / R mod M */
+	memcpy(result, acc, key->len * sizeof(result[0]));
+
+	/* Make sure result < mod; result is at most 1x mod too large. */
+	if (greater_equal_modulus(key, result))
+		subtract_modulus(key, result);
+
+	/* Convert to bigendian byte array */
+	for (i = key->len - 1, ptr = inout; (int)i >= 0; i--, ptr++)
+		put_unaligned_be32(result[i], ptr);
+	return 0;
+}
+
+static void rsa_convert_big_endian(uint32_t *dst, const uint32_t *src, int len)
+{
+	int i;
+
+	for (i = 0; i < len; i++)
+		dst[i] = fdt32_to_cpu(src[len - 1 - i]);
+}
+
+int rsa_mod_exp_sw(const uint8_t *sig, uint32_t sig_len,
+		struct key_prop *prop, uint8_t *out)
+{
+	struct rsa_public_key key;
+	int ret;
+
+	if (!prop) {
+		debug("%s: Skipping invalid prop", __func__);
+		return -EBADF;
+	}
+	key.n0inv = prop->n0inv;
+	key.len = prop->num_bits;
+
+	if (!prop->public_exponent)
+		key.exponent = RSA_DEFAULT_PUBEXP;
+	else
+		key.exponent =
+			fdt64_to_cpu(*((uint64_t *)(prop->public_exponent)));
+
+	if (!key.len || !prop->modulus || !prop->rr) {
+		debug("%s: Missing RSA key info", __func__);
+		return -EFAULT;
+	}
+
+	/* Sanity check for stack size */
+	if (key.len > RSA_MAX_KEY_BITS || key.len < RSA_MIN_KEY_BITS) {
+		debug("RSA key bits %u outside allowed range %d..%d\n",
+		      key.len, RSA_MIN_KEY_BITS, RSA_MAX_KEY_BITS);
+		return -EFAULT;
+	}
+	key.len /= sizeof(uint32_t) * 8;
+	uint32_t key1[key.len], key2[key.len];
+
+	key.modulus = key1;
+	key.rr = key2;
+	rsa_convert_big_endian(key.modulus, (uint32_t *)prop->modulus, key.len);
+	rsa_convert_big_endian(key.rr, (uint32_t *)prop->rr, key.len);
+	if (!key.modulus || !key.rr) {
+		debug("%s: Out of memory", __func__);
+		return -ENOMEM;
+	}
+
+	uint32_t buf[sig_len / sizeof(uint32_t)];
+
+	memcpy(buf, sig, sig_len);
+
+	ret = pow_mod(&key, buf);
+	if (ret)
+		return ret;
+
+	memcpy(out, buf, sig_len);
+
+	return 0;
+}