1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * (pseudo) random functions
4 * Currently uses SHA-256 to scramble the PRNG state.
5 *
6 * Copyright IBM Corp. 2024
7 */
8
9 #include "libcflat.h"
10 #include "rand.h"
11 #include <string.h>
12
13 /* Begin SHA-256 related definitions */
14
15 #define INITAL_HASH { \
16 0x6a09e667, \
17 0xbb67ae85, \
18 0x3c6ef372, \
19 0xa54ff53a, \
20 0x510e527f, \
21 0x9b05688c, \
22 0x1f83d9ab, \
23 0x5be0cd19, \
24 }
25
26 static const uint32_t K[] = {
27 0x428a2f98, 0x71374491, 0xb5c0fbcf, 0xe9b5dba5, 0x3956c25b, 0x59f111f1, 0x923f82a4, 0xab1c5ed5,
28 0xd807aa98, 0x12835b01, 0x243185be, 0x550c7dc3, 0x72be5d74, 0x80deb1fe, 0x9bdc06a7, 0xc19bf174,
29 0xe49b69c1, 0xefbe4786, 0x0fc19dc6, 0x240ca1cc, 0x2de92c6f, 0x4a7484aa, 0x5cb0a9dc, 0x76f988da,
30 0x983e5152, 0xa831c66d, 0xb00327c8, 0xbf597fc7, 0xc6e00bf3, 0xd5a79147, 0x06ca6351, 0x14292967,
31 0x27b70a85, 0x2e1b2138, 0x4d2c6dfc, 0x53380d13, 0x650a7354, 0x766a0abb, 0x81c2c92e, 0x92722c85,
32 0xa2bfe8a1, 0xa81a664b, 0xc24b8b70, 0xc76c51a3, 0xd192e819, 0xd6990624, 0xf40e3585, 0x106aa070,
33 0x19a4c116, 0x1e376c08, 0x2748774c, 0x34b0bcb5, 0x391c0cb3, 0x4ed8aa4a, 0x5b9cca4f, 0x682e6ff3,
34 0x748f82ee, 0x78a5636f, 0x84c87814, 0x8cc70208, 0x90befffa, 0xa4506ceb, 0xbef9a3f7, 0xc67178f2,
35 };
36
ch(uint32_t x,uint32_t y,uint32_t z)37 static inline uint32_t ch(uint32_t x, uint32_t y, uint32_t z)
38 {
39 return (x & y) ^ ((~x) & z);
40 }
41
maj(uint32_t x,uint32_t y,uint32_t z)42 static inline uint32_t maj(uint32_t x, uint32_t y, uint32_t z)
43 {
44 return (x & y) ^ (x & z) ^ (y & z);
45 }
46
rot(uint32_t value,unsigned int count)47 static inline uint32_t rot(uint32_t value, unsigned int count)
48 {
49 return value >> count | value << (32 - count);
50 }
51
upper_sig0(uint32_t x)52 static inline uint32_t upper_sig0(uint32_t x)
53 {
54 return rot(x, 2) ^ rot(x, 13) ^ rot(x, 22);
55 }
56
upper_sig1(uint32_t x)57 static inline uint32_t upper_sig1(uint32_t x)
58 {
59 return rot(x, 6) ^ rot(x, 11) ^ rot(x, 25);
60 }
61
lower_sig0(uint32_t x)62 static inline uint32_t lower_sig0(uint32_t x)
63 {
64 return rot(x, 7) ^ rot(x, 18) ^ (x >> 3);
65 }
66
lower_sig1(uint32_t x)67 static inline uint32_t lower_sig1(uint32_t x)
68 {
69 return rot(x, 17) ^ rot(x, 19) ^ (x >> 10);
70 }
71
72 enum alphabet { A, B, C, D, E, F, G, H, };
73
sha256_chunk(const uint32_t (* chunk)[16],uint32_t (* hash)[8])74 static void sha256_chunk(const uint32_t (*chunk)[16], uint32_t (*hash)[8])
75 {
76 uint32_t w[64];
77 uint32_t w_hash[8];
78
79 memcpy(w, chunk, sizeof(*chunk));
80
81 for (int i = 16; i < 64; i++)
82 w[i] = lower_sig1(w[i - 2]) + w[i - 7] + lower_sig0(w[i - 15]) + w[i - 16];
83
84 memcpy(w_hash, hash, sizeof(*hash));
85
86 for (int i = 0; i < 64; i++) {
87 uint32_t t1, t2;
88
89 t1 = w_hash[H] +
90 upper_sig1(w_hash[E]) +
91 ch(w_hash[E], w_hash[F], w_hash[G]) +
92 K[i] +
93 w[i];
94
95 t2 = upper_sig0(w_hash[A]) + maj(w_hash[A], w_hash[B], w_hash[C]);
96
97 w_hash[H] = w_hash[G];
98 w_hash[G] = w_hash[F];
99 w_hash[F] = w_hash[E];
100 w_hash[E] = w_hash[D] + t1;
101 w_hash[D] = w_hash[C];
102 w_hash[C] = w_hash[B];
103 w_hash[B] = w_hash[A];
104 w_hash[A] = t1 + t2;
105 }
106
107 for (int i = 0; i < 8; i++)
108 (*hash)[i] += w_hash[i];
109 }
110
111 /**
112 * sha256_hash - Calculate SHA-256 of input. Only a limited subset of inputs supported.
113 * @n: Number of words to hash, must be <= 13
114 * @input: Input data to hash
115 * @hash: Output hash as a word array, ordered such that the first word contains
116 * the first/leftmost bits of the 256 bit hash
117 *
118 * Calculate the SHA-256 hash of the input where the input must be a multiple of
119 * 4 bytes and at most 52 long. The input is used without any adjustment, so,
120 * should the caller want to hash bytes it needs to interpret the bytes in the
121 * ordering as defined by the specification, that is big endian.
122 * The same applies to interpreting the output array as bytes.
123 * The function computes the same as: printf "%08x" ${input[@]} | xxd -r -p | sha256sum .
124 */
sha256_hash(unsigned int n,const uint32_t (* input)[n],uint32_t (* hash)[8])125 static void sha256_hash(unsigned int n, const uint32_t (*input)[n], uint32_t (*hash)[8])
126 {
127 /*
128 * Pad according to SHA-2 specification.
129 * First set up length in bits.
130 */
131 uint32_t chunk[16] = {
132 [15] = sizeof(*input) * 8,
133 };
134
135 memcpy(chunk, input, sizeof(*input));
136 /* Then add separator */
137 chunk[n] = 1 << 31;
138 memcpy(hash, (uint32_t[])INITAL_HASH, sizeof(*hash));
139 sha256_chunk(&chunk, hash);
140 }
141
142 /* End SHA-256 related definitions */
143
prng_init(uint64_t seed)144 prng_state prng_init(uint64_t seed)
145 {
146 prng_state state = { .next_word = 0 };
147 uint32_t seed_arr[2] = { seed >> 32, seed };
148
149 sha256_hash(ARRAY_SIZE(seed_arr), &seed_arr, &state.hash);
150 return state;
151 }
152
prng_scramble(prng_state * state)153 static void prng_scramble(prng_state *state)
154 {
155 uint32_t input[8];
156
157 memcpy(input, state->hash, sizeof(state->hash));
158 sha256_hash(ARRAY_SIZE(input), &input, &state->hash);
159 state->next_word = 0;
160 }
161
prng32(prng_state * state)162 uint32_t prng32(prng_state *state)
163 {
164 if (state->next_word < ARRAY_SIZE(state->hash))
165 return state->hash[state->next_word++];
166
167 prng_scramble(state);
168 return prng32(state);
169 }
170
prng64(prng_state * state)171 uint64_t prng64(prng_state *state)
172 {
173 /* explicitly evaluate the high word first */
174 uint64_t high = prng32(state);
175
176 return high << 32 | prng32(state);
177 }
178