1/* $OpenBSD: chacha.c,v 1.2 2023/07/17 05:26:38 djm Exp $ */
2/*
3chacha-merged.c version 20080118
4D. J. Bernstein
5Public domain.
6*/
7
8#include "includes.h"
9
10#include "chacha.h"
11
12typedef unsigned char u8;
13typedef unsigned int u32;
14
15typedef struct chacha_ctx chacha_ctx;
16
17#define U8C(v) (v##U)
18#define U32C(v) (v##U)
19
20#define U8V(v) ((u8)(v) & U8C(0xFF))
21#define U32V(v) ((u32)(v) & U32C(0xFFFFFFFF))
22
23#define ROTL32(v, n) \
24  (U32V((v) << (n)) | ((v) >> (32 - (n))))
25
26#define U8TO32_LITTLE(p) \
27  (((u32)((p)[0])      ) | \
28   ((u32)((p)[1]) <<  8) | \
29   ((u32)((p)[2]) << 16) | \
30   ((u32)((p)[3]) << 24))
31
32#define U32TO8_LITTLE(p, v) \
33  do { \
34    (p)[0] = U8V((v)      ); \
35    (p)[1] = U8V((v) >>  8); \
36    (p)[2] = U8V((v) >> 16); \
37    (p)[3] = U8V((v) >> 24); \
38  } while (0)
39
40#define ROTATE(v,c) (ROTL32(v,c))
41#define XOR(v,w) ((v) ^ (w))
42#define PLUS(v,w) (U32V((v) + (w)))
43#define PLUSONE(v) (PLUS((v),1))
44
45#define QUARTERROUND(a,b,c,d) \
46  a = PLUS(a,b); d = ROTATE(XOR(d,a),16); \
47  c = PLUS(c,d); b = ROTATE(XOR(b,c),12); \
48  a = PLUS(a,b); d = ROTATE(XOR(d,a), 8); \
49  c = PLUS(c,d); b = ROTATE(XOR(b,c), 7);
50
51static const char sigma[16] = "expand 32-byte k";
52static const char tau[16] = "expand 16-byte k";
53
54void
55chacha_keysetup(chacha_ctx *x,const u8 *k,u32 kbits)
56{
57  const char *constants;
58
59  x->input[4] = U8TO32_LITTLE(k + 0);
60  x->input[5] = U8TO32_LITTLE(k + 4);
61  x->input[6] = U8TO32_LITTLE(k + 8);
62  x->input[7] = U8TO32_LITTLE(k + 12);
63  if (kbits == 256) { /* recommended */
64    k += 16;
65    constants = sigma;
66  } else { /* kbits == 128 */
67    constants = tau;
68  }
69  x->input[8] = U8TO32_LITTLE(k + 0);
70  x->input[9] = U8TO32_LITTLE(k + 4);
71  x->input[10] = U8TO32_LITTLE(k + 8);
72  x->input[11] = U8TO32_LITTLE(k + 12);
73  x->input[0] = U8TO32_LITTLE(constants + 0);
74  x->input[1] = U8TO32_LITTLE(constants + 4);
75  x->input[2] = U8TO32_LITTLE(constants + 8);
76  x->input[3] = U8TO32_LITTLE(constants + 12);
77}
78
79void
80chacha_ivsetup(chacha_ctx *x, const u8 *iv, const u8 *counter)
81{
82  x->input[12] = counter == NULL ? 0 : U8TO32_LITTLE(counter + 0);
83  x->input[13] = counter == NULL ? 0 : U8TO32_LITTLE(counter + 4);
84  x->input[14] = U8TO32_LITTLE(iv + 0);
85  x->input[15] = U8TO32_LITTLE(iv + 4);
86}
87
88void
89chacha_encrypt_bytes(chacha_ctx *x,const u8 *m,u8 *c,u32 bytes)
90{
91  u32 x0, x1, x2, x3, x4, x5, x6, x7, x8, x9, x10, x11, x12, x13, x14, x15;
92  u32 j0, j1, j2, j3, j4, j5, j6, j7, j8, j9, j10, j11, j12, j13, j14, j15;
93  u8 *ctarget = NULL;
94  u8 tmp[64];
95  u_int i;
96
97  if (!bytes) return;
98
99  j0 = x->input[0];
100  j1 = x->input[1];
101  j2 = x->input[2];
102  j3 = x->input[3];
103  j4 = x->input[4];
104  j5 = x->input[5];
105  j6 = x->input[6];
106  j7 = x->input[7];
107  j8 = x->input[8];
108  j9 = x->input[9];
109  j10 = x->input[10];
110  j11 = x->input[11];
111  j12 = x->input[12];
112  j13 = x->input[13];
113  j14 = x->input[14];
114  j15 = x->input[15];
115
116  for (;;) {
117    if (bytes < 64) {
118      for (i = 0;i < bytes;++i) tmp[i] = m[i];
119      m = tmp;
120      ctarget = c;
121      c = tmp;
122    }
123    x0 = j0;
124    x1 = j1;
125    x2 = j2;
126    x3 = j3;
127    x4 = j4;
128    x5 = j5;
129    x6 = j6;
130    x7 = j7;
131    x8 = j8;
132    x9 = j9;
133    x10 = j10;
134    x11 = j11;
135    x12 = j12;
136    x13 = j13;
137    x14 = j14;
138    x15 = j15;
139    for (i = 20;i > 0;i -= 2) {
140      QUARTERROUND( x0, x4, x8,x12)
141      QUARTERROUND( x1, x5, x9,x13)
142      QUARTERROUND( x2, x6,x10,x14)
143      QUARTERROUND( x3, x7,x11,x15)
144      QUARTERROUND( x0, x5,x10,x15)
145      QUARTERROUND( x1, x6,x11,x12)
146      QUARTERROUND( x2, x7, x8,x13)
147      QUARTERROUND( x3, x4, x9,x14)
148    }
149    x0 = PLUS(x0,j0);
150    x1 = PLUS(x1,j1);
151    x2 = PLUS(x2,j2);
152    x3 = PLUS(x3,j3);
153    x4 = PLUS(x4,j4);
154    x5 = PLUS(x5,j5);
155    x6 = PLUS(x6,j6);
156    x7 = PLUS(x7,j7);
157    x8 = PLUS(x8,j8);
158    x9 = PLUS(x9,j9);
159    x10 = PLUS(x10,j10);
160    x11 = PLUS(x11,j11);
161    x12 = PLUS(x12,j12);
162    x13 = PLUS(x13,j13);
163    x14 = PLUS(x14,j14);
164    x15 = PLUS(x15,j15);
165
166    x0 = XOR(x0,U8TO32_LITTLE(m + 0));
167    x1 = XOR(x1,U8TO32_LITTLE(m + 4));
168    x2 = XOR(x2,U8TO32_LITTLE(m + 8));
169    x3 = XOR(x3,U8TO32_LITTLE(m + 12));
170    x4 = XOR(x4,U8TO32_LITTLE(m + 16));
171    x5 = XOR(x5,U8TO32_LITTLE(m + 20));
172    x6 = XOR(x6,U8TO32_LITTLE(m + 24));
173    x7 = XOR(x7,U8TO32_LITTLE(m + 28));
174    x8 = XOR(x8,U8TO32_LITTLE(m + 32));
175    x9 = XOR(x9,U8TO32_LITTLE(m + 36));
176    x10 = XOR(x10,U8TO32_LITTLE(m + 40));
177    x11 = XOR(x11,U8TO32_LITTLE(m + 44));
178    x12 = XOR(x12,U8TO32_LITTLE(m + 48));
179    x13 = XOR(x13,U8TO32_LITTLE(m + 52));
180    x14 = XOR(x14,U8TO32_LITTLE(m + 56));
181    x15 = XOR(x15,U8TO32_LITTLE(m + 60));
182
183    j12 = PLUSONE(j12);
184    if (!j12) {
185      j13 = PLUSONE(j13);
186      /* stopping at 2^70 bytes per nonce is user's responsibility */
187    }
188
189    U32TO8_LITTLE(c + 0,x0);
190    U32TO8_LITTLE(c + 4,x1);
191    U32TO8_LITTLE(c + 8,x2);
192    U32TO8_LITTLE(c + 12,x3);
193    U32TO8_LITTLE(c + 16,x4);
194    U32TO8_LITTLE(c + 20,x5);
195    U32TO8_LITTLE(c + 24,x6);
196    U32TO8_LITTLE(c + 28,x7);
197    U32TO8_LITTLE(c + 32,x8);
198    U32TO8_LITTLE(c + 36,x9);
199    U32TO8_LITTLE(c + 40,x10);
200    U32TO8_LITTLE(c + 44,x11);
201    U32TO8_LITTLE(c + 48,x12);
202    U32TO8_LITTLE(c + 52,x13);
203    U32TO8_LITTLE(c + 56,x14);
204    U32TO8_LITTLE(c + 60,x15);
205
206    if (bytes <= 64) {
207      if (bytes < 64) {
208        for (i = 0;i < bytes;++i) ctarget[i] = c[i];
209      }
210      x->input[12] = j12;
211      x->input[13] = j13;
212      return;
213    }
214    bytes -= 64;
215    c += 64;
216    m += 64;
217  }
218}
219