[RFC 2/4] Add rsa support

[Jan Luebbe <jlu@pengutronix.de>]

From: Sascha Hauer <s.hauer@pengutronix.de>

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
---
 crypto/Kconfig              |   3 +
 crypto/Makefile             |   1 +
 crypto/rsa.c                | 411 ++++++++++++++++++++++++++++++++++++++++++++
 include/asm-generic/errno.h |   5 +
 include/rsa.h               |  54 ++++++
 5 files changed, 474 insertions(+)
 create mode 100644 crypto/rsa.c
 create mode 100644 include/rsa.h

diff --git a/crypto/Kconfig b/crypto/Kconfig
index 4bd8dcf359f8..fa9ba491b79b 100644
--- a/crypto/Kconfig
+++ b/crypto/Kconfig
@@ -25,3 +25,6 @@ config SHA256
 	bool "SHA256"
 
 endif
+
+config RSA
+	bool
diff --git a/crypto/Makefile b/crypto/Makefile
index 7c5b035b73de..44be124aa368 100644
--- a/crypto/Makefile
+++ b/crypto/Makefile
@@ -5,3 +5,4 @@ obj-$(CONFIG_MD5)	+= md5.o
 obj-$(CONFIG_SHA1)	+= sha1.o
 obj-$(CONFIG_SHA224)	+= sha2.o
 obj-$(CONFIG_SHA256)	+= sha2.o
+obj-$(CONFIG_RSA)	+= rsa.o
diff --git a/crypto/rsa.c b/crypto/rsa.c
new file mode 100644
index 000000000000..6a0c7b8a15cc
--- /dev/null
+++ b/crypto/rsa.c
@@ -0,0 +1,411 @@
+/*
+ * Copyright (c) 2013, Google Inc.
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#include <common.h>
+#include <malloc.h>
+#include <of.h>
+#include <digest.h>
+#include <asm/types.h>
+#include <asm/byteorder.h>
+#include <errno.h>
+#include <rsa.h>
+#include <asm/types.h>
+#include <asm/unaligned.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
+
+/* This is the minimum/maximum key size we support, in bits */
+#define RSA_MIN_KEY_BITS	1024
+#define RSA_MAX_KEY_BITS	4096
+
+/**
+ * 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, void *__inout)
+{
+	uint32_t *inout = __inout;
+	uint32_t *result, *ptr;
+	uint i;
+	int j, k;
+	uint32_t val[RSA_MAX_KEY_BITS / 32], acc[RSA_MAX_KEY_BITS / 32], tmp[RSA_MAX_KEY_BITS / 32];
+	uint32_t a_scaled[RSA_MAX_KEY_BITS / 32];
+
+	/* 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;
+	}
+
+	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;
+}
+
+/*
+ * Hash algorithm OIDs plus ASN.1 DER wrappings [RFC4880 sec 5.2.2].
+ */
+static const u8 RSA_digest_info_MD5[] = {
+	0x30, 0x20, 0x30, 0x0C, 0x06, 0x08,
+	0x2A, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x02, 0x05, /* OID */
+	0x05, 0x00, 0x04, 0x10
+};
+
+static const u8 RSA_digest_info_SHA1[] = {
+	0x30, 0x21, 0x30, 0x09, 0x06, 0x05,
+	0x2B, 0x0E, 0x03, 0x02, 0x1A,
+	0x05, 0x00, 0x04, 0x14
+};
+
+static const u8 RSA_digest_info_RIPE_MD_160[] = {
+	0x30, 0x21, 0x30, 0x09, 0x06, 0x05,
+	0x2B, 0x24, 0x03, 0x02, 0x01,
+	0x05, 0x00, 0x04, 0x14
+};
+
+static const u8 RSA_digest_info_SHA224[] = {
+	0x30, 0x2d, 0x30, 0x0d, 0x06, 0x09,
+	0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x04,
+	0x05, 0x00, 0x04, 0x1C
+};
+
+static const u8 RSA_digest_info_SHA256[] = {
+	0x30, 0x31, 0x30, 0x0d, 0x06, 0x09,
+	0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x01,
+	0x05, 0x00, 0x04, 0x20
+};
+
+static const u8 RSA_digest_info_SHA384[] = {
+	0x30, 0x41, 0x30, 0x0d, 0x06, 0x09,
+	0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x02,
+	0x05, 0x00, 0x04, 0x30
+};
+
+static const u8 RSA_digest_info_SHA512[] = {
+	0x30, 0x51, 0x30, 0x0d, 0x06, 0x09,
+	0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x03,
+	0x05, 0x00, 0x04, 0x40
+};
+
+static const struct {
+	const u8 *data;
+	size_t size;
+} RSA_ASN1_templates[] = {
+#define _(X) { RSA_digest_info_##X, sizeof(RSA_digest_info_##X) }
+	[HASH_ALGO_MD5]		= _(MD5),
+	[HASH_ALGO_SHA1]	= _(SHA1),
+	[HASH_ALGO_RIPE_MD_160]	= _(RIPE_MD_160),
+	[HASH_ALGO_SHA256]	= _(SHA256),
+	[HASH_ALGO_SHA384]	= _(SHA384),
+	[HASH_ALGO_SHA512]	= _(SHA512),
+	[HASH_ALGO_SHA224]	= _(SHA224),
+#undef _
+};
+
+int rsa_verify(const struct rsa_public_key *key, const uint8_t *sig,
+			  const uint32_t sig_len, const uint8_t *hash,
+			  enum hash_algo algo)
+{
+	int ret;
+	uint8_t buf[RSA_MAX_SIG_BITS / 8];
+	int i;
+	unsigned PS_end, T_offset;
+	const u8 *asn1_template = RSA_ASN1_templates[algo].data;
+	size_t asn1_size = RSA_ASN1_templates[algo].size;
+	struct digest *d = digest_get(algo);
+
+	if (!d)
+		return -EOPNOTSUPP;
+
+	if (sig_len != (key->len * sizeof(uint32_t))) {
+		debug("Signature is of incorrect length %d, should be %d\n", sig_len,
+				key->len * sizeof(uint32_t));
+		return -EINVAL;
+	}
+
+	/* Sanity check for stack size */
+	if (sig_len > RSA_MAX_SIG_BITS / 8) {
+		debug("Signature length %u exceeds maximum %d\n", sig_len,
+		      RSA_MAX_SIG_BITS / 8);
+		return -EINVAL;
+	}
+
+	memcpy(buf, sig, sig_len);
+
+	ret = pow_mod(key, buf);
+	if (ret)
+		return ret;
+
+	T_offset = sig_len - (asn1_size + d->length);
+
+	PS_end = T_offset - 1;
+	if (buf[PS_end] != 0x00) {
+		pr_err(" = -EBADMSG [EM[T-1] == %02u]", buf[PS_end]);
+		return -EBADMSG;
+	}
+
+	for (i = 2; i < PS_end; i++) {
+		if (buf[i] != 0xff) {
+			pr_err(" = -EBADMSG [EM[PS%x] == %02u]", i - 2, buf[i]);
+			return -EBADMSG;
+		}
+	}
+
+	if (memcmp(asn1_template, buf + T_offset, asn1_size) != 0) {
+		pr_err(" = -EBADMSG [EM[T] ASN.1 mismatch]");
+		return -EBADMSG;
+	}
+
+	if (memcmp(hash, buf + T_offset + asn1_size, d->length) != 0) {
+		pr_err(" = -EKEYREJECTED [EM[T] hash mismatch]");
+		return -EKEYREJECTED;
+	}
+
+	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_of_read_key(struct device_node *node, struct rsa_public_key *key)
+{
+	const void *modulus, *rr;
+	const uint64_t *public_exponent;
+	int length;
+
+	of_property_read_u32(node, "rsa,num-bits", &key->len);
+	of_property_read_u32(node, "rsa,n0-inverse", &key->n0inv);
+
+	public_exponent = of_get_property(node, "rsa,exponent", &length);
+	if (!public_exponent || length < sizeof(*public_exponent))
+		key->exponent = RSA_DEFAULT_PUBEXP;
+	else
+		key->exponent = fdt64_to_cpu(*public_exponent);
+
+	modulus = of_get_property(node, "rsa,modulus", NULL);
+	rr = of_get_property(node, "rsa,r-squared", NULL);
+
+	if (!key->len || !modulus || !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;
+
+	key->modulus = xzalloc(RSA_MAX_KEY_BITS / 8);
+	key->rr = xzalloc(RSA_MAX_KEY_BITS / 8);
+
+	rsa_convert_big_endian(key->modulus, modulus, key->len);
+	rsa_convert_big_endian(key->rr, rr, key->len);
+
+	return 0;
+}
diff --git a/include/asm-generic/errno.h b/include/asm-generic/errno.h
index bbf493c373ae..b239831bc703 100644
--- a/include/asm-generic/errno.h
+++ b/include/asm-generic/errno.h
@@ -126,6 +126,11 @@
 
 #define	ENOMEDIUM	123	/* No medium found */
 #define	EMEDIUMTYPE	124	/* Wrong medium type */
+#define	ECANCELED	125	/* Operation Canceled */
+#define	ENOKEY		126	/* Required key not available */
+#define	EKEYEXPIRED	127	/* Key has expired */
+#define	EKEYREVOKED	128	/* Key has been revoked */
+#define	EKEYREJECTED	129	/* Key was rejected by service */
 
 /* Should never be seen by user programs */
 #define ERESTARTSYS	512
diff --git a/include/rsa.h b/include/rsa.h
new file mode 100644
index 000000000000..feb8c3120023
--- /dev/null
+++ b/include/rsa.h
@@ -0,0 +1,54 @@
+/*
+ * Copyright (c) 2013, Google Inc.
+ *
+ * (C) Copyright 2008 Semihalf
+ *
+ * (C) Copyright 2000-2006
+ * Wolfgang Denk, DENX Software Engineering, wd@denx.de.
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#ifndef _RSA_H
+#define _RSA_H
+
+#include <errno.h>
+#include <digest.h>
+
+/**
+ * struct rsa_public_key - holder for a public key
+ *
+ * An RSA public key consists of a modulus (typically called N), the inverse
+ * and R^2, where R is 2^(# key bits).
+ */
+
+struct rsa_public_key {
+	uint len;		/* len of modulus[] in number of uint32_t */
+	uint32_t n0inv;		/* -1 / modulus[0] mod 2^32 */
+	uint32_t *modulus;	/* modulus as little endian array */
+	uint32_t *rr;		/* R^2 as little endian array */
+	uint64_t exponent;	/* public exponent */
+};
+
+/**
+ * rsa_verify() - Verify a signature against some data
+ *
+ * Verify a RSA PKCS1.5 signature against an expected hash.
+ *
+ * @info:	Specifies key and FIT information
+ * @data:	Pointer to the input data
+ * @data_len:	Data length
+ * @sig:	Signature
+ * @sig_len:	Number of bytes in signature
+ * @return 0 if verified, -ve on error
+ */
+int rsa_verify(const struct rsa_public_key *key, const uint8_t *sig,
+			  const uint32_t sig_len, const uint8_t *hash,
+			  enum hash_algo algo);
+
+/* This is the maximum signature length that we support, in bits */
+#define RSA_MAX_SIG_BITS	4096
+
+int rsa_of_read_key(struct device_node *node, struct rsa_public_key *key);
+
+#endif
-- 
2.1.4


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