1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /*
3  * The "hash function" used as the core of the ChaCha stream cipher (RFC7539)
4  *
5  * Copyright (C) 2015 Martin Willi
6  */
7 
8 #include <linux/bug.h>
9 #include <linux/kernel.h>
10 #include <linux/export.h>
11 #include <linux/bitops.h>
12 #include <linux/string.h>
13 #include <asm/unaligned.h>
14 #include <crypto/chacha.h>
15 
chacha_permute(u32 * x,int nrounds)16 static void chacha_permute(u32 *x, int nrounds)
17 {
18 	int i;
19 
20 	/* whitelist the allowed round counts */
21 	WARN_ON_ONCE(nrounds != 20 && nrounds != 12);
22 
23 	for (i = 0; i < nrounds; i += 2) {
24 		x[0]  += x[4];    x[12] = rol32(x[12] ^ x[0],  16);
25 		x[1]  += x[5];    x[13] = rol32(x[13] ^ x[1],  16);
26 		x[2]  += x[6];    x[14] = rol32(x[14] ^ x[2],  16);
27 		x[3]  += x[7];    x[15] = rol32(x[15] ^ x[3],  16);
28 
29 		x[8]  += x[12];   x[4]  = rol32(x[4]  ^ x[8],  12);
30 		x[9]  += x[13];   x[5]  = rol32(x[5]  ^ x[9],  12);
31 		x[10] += x[14];   x[6]  = rol32(x[6]  ^ x[10], 12);
32 		x[11] += x[15];   x[7]  = rol32(x[7]  ^ x[11], 12);
33 
34 		x[0]  += x[4];    x[12] = rol32(x[12] ^ x[0],   8);
35 		x[1]  += x[5];    x[13] = rol32(x[13] ^ x[1],   8);
36 		x[2]  += x[6];    x[14] = rol32(x[14] ^ x[2],   8);
37 		x[3]  += x[7];    x[15] = rol32(x[15] ^ x[3],   8);
38 
39 		x[8]  += x[12];   x[4]  = rol32(x[4]  ^ x[8],   7);
40 		x[9]  += x[13];   x[5]  = rol32(x[5]  ^ x[9],   7);
41 		x[10] += x[14];   x[6]  = rol32(x[6]  ^ x[10],  7);
42 		x[11] += x[15];   x[7]  = rol32(x[7]  ^ x[11],  7);
43 
44 		x[0]  += x[5];    x[15] = rol32(x[15] ^ x[0],  16);
45 		x[1]  += x[6];    x[12] = rol32(x[12] ^ x[1],  16);
46 		x[2]  += x[7];    x[13] = rol32(x[13] ^ x[2],  16);
47 		x[3]  += x[4];    x[14] = rol32(x[14] ^ x[3],  16);
48 
49 		x[10] += x[15];   x[5]  = rol32(x[5]  ^ x[10], 12);
50 		x[11] += x[12];   x[6]  = rol32(x[6]  ^ x[11], 12);
51 		x[8]  += x[13];   x[7]  = rol32(x[7]  ^ x[8],  12);
52 		x[9]  += x[14];   x[4]  = rol32(x[4]  ^ x[9],  12);
53 
54 		x[0]  += x[5];    x[15] = rol32(x[15] ^ x[0],   8);
55 		x[1]  += x[6];    x[12] = rol32(x[12] ^ x[1],   8);
56 		x[2]  += x[7];    x[13] = rol32(x[13] ^ x[2],   8);
57 		x[3]  += x[4];    x[14] = rol32(x[14] ^ x[3],   8);
58 
59 		x[10] += x[15];   x[5]  = rol32(x[5]  ^ x[10],  7);
60 		x[11] += x[12];   x[6]  = rol32(x[6]  ^ x[11],  7);
61 		x[8]  += x[13];   x[7]  = rol32(x[7]  ^ x[8],   7);
62 		x[9]  += x[14];   x[4]  = rol32(x[4]  ^ x[9],   7);
63 	}
64 }
65 
66 /**
67  * chacha_block_generic - generate one keystream block and increment block counter
68  * @state: input state matrix (16 32-bit words)
69  * @stream: output keystream block (64 bytes)
70  * @nrounds: number of rounds (20 or 12; 20 is recommended)
71  *
72  * This is the ChaCha core, a function from 64-byte strings to 64-byte strings.
73  * The caller has already converted the endianness of the input.  This function
74  * also handles incrementing the block counter in the input matrix.
75  */
chacha_block_generic(u32 * state,u8 * stream,int nrounds)76 void chacha_block_generic(u32 *state, u8 *stream, int nrounds)
77 {
78 	u32 x[16];
79 	int i;
80 
81 	memcpy(x, state, 64);
82 
83 	chacha_permute(x, nrounds);
84 
85 	for (i = 0; i < ARRAY_SIZE(x); i++)
86 		put_unaligned_le32(x[i] + state[i], &stream[i * sizeof(u32)]);
87 
88 	state[12]++;
89 }
90 EXPORT_SYMBOL(chacha_block_generic);
91 
92 /**
93  * hchacha_block_generic - abbreviated ChaCha core, for XChaCha
94  * @state: input state matrix (16 32-bit words)
95  * @stream: output (8 32-bit words)
96  * @nrounds: number of rounds (20 or 12; 20 is recommended)
97  *
98  * HChaCha is the ChaCha equivalent of HSalsa and is an intermediate step
99  * towards XChaCha (see https://cr.yp.to/snuffle/xsalsa-20081128.pdf).  HChaCha
100  * skips the final addition of the initial state, and outputs only certain words
101  * of the state.  It should not be used for streaming directly.
102  */
hchacha_block_generic(const u32 * state,u32 * stream,int nrounds)103 void hchacha_block_generic(const u32 *state, u32 *stream, int nrounds)
104 {
105 	u32 x[16];
106 
107 	memcpy(x, state, 64);
108 
109 	chacha_permute(x, nrounds);
110 
111 	memcpy(&stream[0], &x[0], 16);
112 	memcpy(&stream[4], &x[12], 16);
113 }
114 EXPORT_SYMBOL(hchacha_block_generic);
115