]>
git.ipfire.org Git - people/ms/u-boot.git/blob - lib/rsa/rsa-mod-exp.c
2 * Copyright (c) 2013, Google Inc.
4 * SPDX-License-Identifier: GPL-2.0+
10 #include <asm/types.h>
11 #include <asm/byteorder.h>
12 #include <linux/errno.h>
13 #include <asm/types.h>
14 #include <asm/unaligned.h>
18 #include <fdt_support.h>
20 #include <u-boot/rsa.h>
21 #include <u-boot/rsa-mod-exp.h>
23 #define UINT64_MULT32(v, multby) (((uint64_t)(v)) * ((uint32_t)(multby)))
25 #define get_unaligned_be32(a) fdt32_to_cpu(*(uint32_t *)a)
26 #define put_unaligned_be32(a, b) (*(uint32_t *)(b) = cpu_to_fdt32(a))
28 /* Default public exponent for backward compatibility */
29 #define RSA_DEFAULT_PUBEXP 65537
32 * subtract_modulus() - subtract modulus from the given value
34 * @key: Key containing modulus to subtract
35 * @num: Number to subtract modulus from, as little endian word array
37 static void subtract_modulus(const struct rsa_public_key
*key
, uint32_t num
[])
42 for (i
= 0; i
< key
->len
; i
++) {
43 acc
+= (uint64_t)num
[i
] - key
->modulus
[i
];
44 num
[i
] = (uint32_t)acc
;
50 * greater_equal_modulus() - check if a value is >= modulus
52 * @key: Key containing modulus to check
53 * @num: Number to check against modulus, as little endian word array
54 * @return 0 if num < modulus, 1 if num >= modulus
56 static int greater_equal_modulus(const struct rsa_public_key
*key
,
61 for (i
= (int)key
->len
- 1; i
>= 0; i
--) {
62 if (num
[i
] < key
->modulus
[i
])
64 if (num
[i
] > key
->modulus
[i
])
72 * montgomery_mul_add_step() - Perform montgomery multiply-add step
74 * Operation: montgomery result[] += a * b[] / n0inv % modulus
77 * @result: Place to put result, as little endian word array
79 * @b: Multiplicand, as little endian word array
81 static void montgomery_mul_add_step(const struct rsa_public_key
*key
,
82 uint32_t result
[], const uint32_t a
, const uint32_t b
[])
84 uint64_t acc_a
, acc_b
;
88 acc_a
= (uint64_t)a
* b
[0] + result
[0];
89 d0
= (uint32_t)acc_a
* key
->n0inv
;
90 acc_b
= (uint64_t)d0
* key
->modulus
[0] + (uint32_t)acc_a
;
91 for (i
= 1; i
< key
->len
; i
++) {
92 acc_a
= (acc_a
>> 32) + (uint64_t)a
* b
[i
] + result
[i
];
93 acc_b
= (acc_b
>> 32) + (uint64_t)d0
* key
->modulus
[i
] +
95 result
[i
- 1] = (uint32_t)acc_b
;
98 acc_a
= (acc_a
>> 32) + (acc_b
>> 32);
100 result
[i
- 1] = (uint32_t)acc_a
;
103 subtract_modulus(key
, result
);
107 * montgomery_mul() - Perform montgomery mutitply
109 * Operation: montgomery result[] = a[] * b[] / n0inv % modulus
112 * @result: Place to put result, as little endian word array
113 * @a: Multiplier, as little endian word array
114 * @b: Multiplicand, as little endian word array
116 static void montgomery_mul(const struct rsa_public_key
*key
,
117 uint32_t result
[], uint32_t a
[], const uint32_t b
[])
121 for (i
= 0; i
< key
->len
; ++i
)
123 for (i
= 0; i
< key
->len
; ++i
)
124 montgomery_mul_add_step(key
, result
, a
[i
], b
);
128 * num_pub_exponent_bits() - Number of bits in the public exponent
131 * @num_bits: Storage for the number of public exponent bits
133 static int num_public_exponent_bits(const struct rsa_public_key
*key
,
138 const uint max_bits
= (sizeof(exponent
) * 8);
140 exponent
= key
->exponent
;
144 *num_bits
= exponent_bits
;
148 for (exponent_bits
= 1; exponent_bits
< max_bits
+ 1; ++exponent_bits
)
149 if (!(exponent
>>= 1)) {
150 *num_bits
= exponent_bits
;
158 * is_public_exponent_bit_set() - Check if a bit in the public exponent is set
161 * @pos: The bit position to check
163 static int is_public_exponent_bit_set(const struct rsa_public_key
*key
,
166 return key
->exponent
& (1ULL << pos
);
170 * pow_mod() - in-place public exponentiation
173 * @inout: Big-endian word array containing value and result
175 static int pow_mod(const struct rsa_public_key
*key
, uint32_t *inout
)
177 uint32_t *result
, *ptr
;
181 /* Sanity check for stack size - key->len is in 32-bit words */
182 if (key
->len
> RSA_MAX_KEY_BITS
/ 32) {
183 debug("RSA key words %u exceeds maximum %d\n", key
->len
,
184 RSA_MAX_KEY_BITS
/ 32);
188 uint32_t val
[key
->len
], acc
[key
->len
], tmp
[key
->len
];
189 uint32_t a_scaled
[key
->len
];
190 result
= tmp
; /* Re-use location. */
192 /* Convert from big endian byte array to little endian word array. */
193 for (i
= 0, ptr
= inout
+ key
->len
- 1; i
< key
->len
; i
++, ptr
--)
194 val
[i
] = get_unaligned_be32(ptr
);
196 if (0 != num_public_exponent_bits(key
, &k
))
200 debug("Public exponent is too short (%d bits, minimum 2)\n",
205 if (!is_public_exponent_bit_set(key
, 0)) {
206 debug("LSB of RSA public exponent must be set.\n");
210 /* the bit at e[k-1] is 1 by definition, so start with: C := M */
211 montgomery_mul(key
, acc
, val
, key
->rr
); /* acc = a * RR / R mod n */
212 /* retain scaled version for intermediate use */
213 memcpy(a_scaled
, acc
, key
->len
* sizeof(a_scaled
[0]));
215 for (j
= k
- 2; j
> 0; --j
) {
216 montgomery_mul(key
, tmp
, acc
, acc
); /* tmp = acc^2 / R mod n */
218 if (is_public_exponent_bit_set(key
, j
)) {
219 /* acc = tmp * val / R mod n */
220 montgomery_mul(key
, acc
, tmp
, a_scaled
);
222 /* e[j] == 0, copy tmp back to acc for next operation */
223 memcpy(acc
, tmp
, key
->len
* sizeof(acc
[0]));
227 /* the bit at e[0] is always 1 */
228 montgomery_mul(key
, tmp
, acc
, acc
); /* tmp = acc^2 / R mod n */
229 montgomery_mul(key
, acc
, tmp
, val
); /* acc = tmp * a / R mod M */
230 memcpy(result
, acc
, key
->len
* sizeof(result
[0]));
232 /* Make sure result < mod; result is at most 1x mod too large. */
233 if (greater_equal_modulus(key
, result
))
234 subtract_modulus(key
, result
);
236 /* Convert to bigendian byte array */
237 for (i
= key
->len
- 1, ptr
= inout
; (int)i
>= 0; i
--, ptr
++)
238 put_unaligned_be32(result
[i
], ptr
);
242 static void rsa_convert_big_endian(uint32_t *dst
, const uint32_t *src
, int len
)
246 for (i
= 0; i
< len
; i
++)
247 dst
[i
] = fdt32_to_cpu(src
[len
- 1 - i
]);
250 int rsa_mod_exp_sw(const uint8_t *sig
, uint32_t sig_len
,
251 struct key_prop
*prop
, uint8_t *out
)
253 struct rsa_public_key key
;
257 debug("%s: Skipping invalid prop", __func__
);
260 key
.n0inv
= prop
->n0inv
;
261 key
.len
= prop
->num_bits
;
263 if (!prop
->public_exponent
)
264 key
.exponent
= RSA_DEFAULT_PUBEXP
;
267 fdt64_to_cpu(*((uint64_t *)(prop
->public_exponent
)));
269 if (!key
.len
|| !prop
->modulus
|| !prop
->rr
) {
270 debug("%s: Missing RSA key info", __func__
);
274 /* Sanity check for stack size */
275 if (key
.len
> RSA_MAX_KEY_BITS
|| key
.len
< RSA_MIN_KEY_BITS
) {
276 debug("RSA key bits %u outside allowed range %d..%d\n",
277 key
.len
, RSA_MIN_KEY_BITS
, RSA_MAX_KEY_BITS
);
280 key
.len
/= sizeof(uint32_t) * 8;
281 uint32_t key1
[key
.len
], key2
[key
.len
];
285 rsa_convert_big_endian(key
.modulus
, (uint32_t *)prop
->modulus
, key
.len
);
286 rsa_convert_big_endian(key
.rr
, (uint32_t *)prop
->rr
, key
.len
);
287 if (!key
.modulus
|| !key
.rr
) {
288 debug("%s: Out of memory", __func__
);
292 uint32_t buf
[sig_len
/ sizeof(uint32_t)];
294 memcpy(buf
, sig
, sig_len
);
296 ret
= pow_mod(&key
, buf
);
300 memcpy(out
, buf
, sig_len
);