1// Based on Go stdlib implementation
2
3const std = @import("../std.zig");
4const mem = std.mem;
5const debug = std.debug;
6
7/// Counter mode.
8///
9/// This mode creates a key stream by encrypting an incrementing counter using a block cipher, and adding it to the source material.
10///
11/// Important: the counter mode doesn't provide authenticated encryption: the ciphertext can be trivially modified without this being detected.
12/// As a result, applications should generally never use it directly, but only in a construction that includes a MAC.
13pub fn ctr(comptime BlockCipher: anytype, block_cipher: BlockCipher, dst: []u8, src: []const u8, iv: [BlockCipher.block_length]u8, endian: std.builtin.Endian) void {
14 ctrSlice(BlockCipher, block_cipher, dst, src, iv, endian, 0, BlockCipher.block_length);
15}
16
17/// Counter mode with configurable counter position and size.
18///
19/// This extended version allows specifying where the counter is located within the IV block
20/// and how many bytes it occupies. This is useful for modes like AES-GCM-SIV which use a
21/// 32-bit counter at the beginning of the block.
22///
23/// @param counter_offset: Byte offset where the counter starts
24/// @param counter_size: Size of the counter in bytes
25pub fn ctrSlice(
26 comptime BlockCipher: anytype,
27 block_cipher: BlockCipher,
28 dst: []u8,
29 src: []const u8,
30 iv: [BlockCipher.block_length]u8,
31 endian: std.builtin.Endian,
32 comptime counter_offset: usize,
33 comptime counter_size: usize,
34) void {
35 debug.assert(dst.len >= src.len);
36 const block_length = BlockCipher.block_length;
37 debug.assert(counter_offset + counter_size <= block_length);
38 debug.assert(counter_size > 0 and counter_size <= block_length);
39
40 var counterBlock = iv;
41 var i: usize = 0;
42
43 const CounterInt = @Int(.unsigned, counter_size * 8);
44
45 const parallel_count = BlockCipher.block.parallel.optimal_parallel_blocks;
46 const wide_block_length = parallel_count * block_length;
47 var cnt_val = mem.readInt(CounterInt, counterBlock[counter_offset..][0..counter_size], endian);
48 if (src.len >= wide_block_length) {
49 var counters: [parallel_count * block_length]u8 = undefined;
50 inline for (0..parallel_count) |j| {
51 counters[j * block_length ..][0..block_length].* = iv;
52 }
53 while (i + wide_block_length <= src.len) : (i += wide_block_length) {
54 comptime var j = 0;
55 inline while (j < parallel_count) : (j += 1) {
56 mem.writeInt(CounterInt, counters[j * block_length + counter_offset ..][0..counter_size], cnt_val +% j, endian);
57 }
58 cnt_val +%= parallel_count;
59 block_cipher.xorWide(parallel_count, dst[i .. i + wide_block_length][0..wide_block_length], src[i .. i + wide_block_length][0..wide_block_length], counters);
60 }
61 mem.writeInt(CounterInt, counterBlock[counter_offset..][0..counter_size], cnt_val, endian);
62 }
63 while (i + block_length <= src.len) : (i += block_length) {
64 block_cipher.xor(dst[i .. i + block_length][0..block_length], src[i .. i + block_length][0..block_length], counterBlock);
65 cnt_val +%= 1;
66 mem.writeInt(CounterInt, counterBlock[counter_offset..][0..counter_size], cnt_val, endian);
67 }
68 if (i < src.len) {
69 var pad: [block_length]u8 = @splat(0);
70 const src_slice = src[i..];
71 @memcpy(pad[0..src_slice.len], src_slice);
72 block_cipher.xor(&pad, &pad, counterBlock);
73 const pad_slice = pad[0 .. src.len - i];
74 @memcpy(dst[i..][0..pad_slice.len], pad_slice);
75 }
76}
77
78test "ctr mode" {
79 const testing = std.testing;
80 const aes = std.crypto.core.aes;
81
82 // Test key and IV from NIST SP 800-38A
83 const key = [_]u8{ 0x2b, 0x7e, 0x15, 0x16, 0x28, 0xae, 0xd2, 0xa6, 0xab, 0xf7, 0x15, 0x88, 0x09, 0xcf, 0x4f, 0x3c };
84 const iv = [_]u8{ 0xf0, 0xf1, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7, 0xf8, 0xf9, 0xfa, 0xfb, 0xfc, 0xfd, 0xfe, 0xff };
85 const ctx = aes.Aes128.initEnc(key);
86
87 // Test 1: Empty input
88 {
89 const in = [_]u8{};
90 const expected = [_]u8{};
91 var out: [0]u8 = undefined;
92 ctr(aes.AesEncryptCtx(aes.Aes128), ctx, out[0..], in[0..], iv, std.builtin.Endian.big);
93 try testing.expectEqualSlices(u8, expected[0..], out[0..]);
94 }
95
96 // Test 2: Single byte
97 {
98 const in = [_]u8{0x6b};
99 const expected = [_]u8{0x87};
100 var out: [1]u8 = undefined;
101 ctr(aes.AesEncryptCtx(aes.Aes128), ctx, out[0..], in[0..], iv, std.builtin.Endian.big);
102 try testing.expectEqualSlices(u8, expected[0..], out[0..]);
103 }
104
105 // Test 3: Less than one block (15 bytes)
106 {
107 const in = [_]u8{ 0x6b, 0xc1, 0xbe, 0xe2, 0x2e, 0x40, 0x9f, 0x96, 0xe9, 0x3d, 0x7e, 0x11, 0x73, 0x93, 0x17 };
108 const expected = [_]u8{ 0x87, 0x4d, 0x61, 0x91, 0xb6, 0x20, 0xe3, 0x26, 0x1b, 0xef, 0x68, 0x64, 0x99, 0x0d, 0xb6 };
109 var out: [15]u8 = undefined;
110 ctr(aes.AesEncryptCtx(aes.Aes128), ctx, out[0..], in[0..], iv, std.builtin.Endian.big);
111 try testing.expectEqualSlices(u8, expected[0..], out[0..]);
112 }
113
114 // Test 4: Exactly one block (16 bytes)
115 {
116 const in = [_]u8{ 0x6b, 0xc1, 0xbe, 0xe2, 0x2e, 0x40, 0x9f, 0x96, 0xe9, 0x3d, 0x7e, 0x11, 0x73, 0x93, 0x17, 0x2a };
117 const expected = [_]u8{ 0x87, 0x4d, 0x61, 0x91, 0xb6, 0x20, 0xe3, 0x26, 0x1b, 0xef, 0x68, 0x64, 0x99, 0x0d, 0xb6, 0xce };
118 var out: [16]u8 = undefined;
119 ctr(aes.AesEncryptCtx(aes.Aes128), ctx, out[0..], in[0..], iv, std.builtin.Endian.big);
120 try testing.expectEqualSlices(u8, expected[0..], out[0..]);
121 }
122
123 // Test 5: One block plus one byte (17 bytes)
124 {
125 const in = [_]u8{ 0x6b, 0xc1, 0xbe, 0xe2, 0x2e, 0x40, 0x9f, 0x96, 0xe9, 0x3d, 0x7e, 0x11, 0x73, 0x93, 0x17, 0x2a, 0xae };
126 const expected = [_]u8{ 0x87, 0x4d, 0x61, 0x91, 0xb6, 0x20, 0xe3, 0x26, 0x1b, 0xef, 0x68, 0x64, 0x99, 0x0d, 0xb6, 0xce, 0x98 };
127 var out: [17]u8 = undefined;
128 ctr(aes.AesEncryptCtx(aes.Aes128), ctx, out[0..], in[0..], iv, std.builtin.Endian.big);
129 try testing.expectEqualSlices(u8, expected[0..], out[0..]);
130 }
131
132 // Test 6: Exactly two blocks (32 bytes)
133 {
134 const in = [_]u8{
135 0x6b, 0xc1, 0xbe, 0xe2, 0x2e, 0x40, 0x9f, 0x96, 0xe9, 0x3d, 0x7e, 0x11, 0x73, 0x93, 0x17, 0x2a,
136 0xae, 0x2d, 0x8a, 0x57, 0x1e, 0x03, 0xac, 0x9c, 0x9e, 0xb7, 0x6f, 0xac, 0x45, 0xaf, 0x8e, 0x51,
137 };
138 const expected = [_]u8{
139 0x87, 0x4d, 0x61, 0x91, 0xb6, 0x20, 0xe3, 0x26, 0x1b, 0xef, 0x68, 0x64, 0x99, 0x0d, 0xb6, 0xce,
140 0x98, 0x06, 0xf6, 0x6b, 0x79, 0x70, 0xfd, 0xff, 0x86, 0x17, 0x18, 0x7b, 0xb9, 0xff, 0xfd, 0xff,
141 };
142 var out: [32]u8 = undefined;
143 ctr(aes.AesEncryptCtx(aes.Aes128), ctx, out[0..], in[0..], iv, std.builtin.Endian.big);
144 try testing.expectEqualSlices(u8, expected[0..], out[0..]);
145 }
146
147 // Test 7: Two blocks plus 5 bytes (37 bytes)
148 {
149 const in = [_]u8{
150 0x6b, 0xc1, 0xbe, 0xe2, 0x2e, 0x40, 0x9f, 0x96, 0xe9, 0x3d, 0x7e, 0x11, 0x73, 0x93, 0x17, 0x2a,
151 0xae, 0x2d, 0x8a, 0x57, 0x1e, 0x03, 0xac, 0x9c, 0x9e, 0xb7, 0x6f, 0xac, 0x45, 0xaf, 0x8e, 0x51,
152 0x30, 0xc8, 0x1c, 0x46, 0xa3,
153 };
154 const expected = [_]u8{
155 0x87, 0x4d, 0x61, 0x91, 0xb6, 0x20, 0xe3, 0x26, 0x1b, 0xef, 0x68, 0x64, 0x99, 0x0d, 0xb6, 0xce,
156 0x98, 0x06, 0xf6, 0x6b, 0x79, 0x70, 0xfd, 0xff, 0x86, 0x17, 0x18, 0x7b, 0xb9, 0xff, 0xfd, 0xff,
157 0x5a, 0xe4, 0xdf, 0x3e, 0xdb,
158 };
159 var out: [37]u8 = undefined;
160 ctr(aes.AesEncryptCtx(aes.Aes128), ctx, out[0..], in[0..], iv, std.builtin.Endian.big);
161 try testing.expectEqualSlices(u8, expected[0..], out[0..]);
162 }
163
164 // Test 8: Four blocks (64 bytes) - NIST test vector
165 {
166 const in = [_]u8{
167 0x6b, 0xc1, 0xbe, 0xe2, 0x2e, 0x40, 0x9f, 0x96, 0xe9, 0x3d, 0x7e, 0x11, 0x73, 0x93, 0x17, 0x2a,
168 0xae, 0x2d, 0x8a, 0x57, 0x1e, 0x03, 0xac, 0x9c, 0x9e, 0xb7, 0x6f, 0xac, 0x45, 0xaf, 0x8e, 0x51,
169 0x30, 0xc8, 0x1c, 0x46, 0xa3, 0x5c, 0xe4, 0x11, 0xe5, 0xfb, 0xc1, 0x19, 0x1a, 0x0a, 0x52, 0xef,
170 0xf6, 0x9f, 0x24, 0x45, 0xdf, 0x4f, 0x9b, 0x17, 0xad, 0x2b, 0x41, 0x7b, 0xe6, 0x6c, 0x37, 0x10,
171 };
172 const expected = [_]u8{
173 0x87, 0x4d, 0x61, 0x91, 0xb6, 0x20, 0xe3, 0x26, 0x1b, 0xef, 0x68, 0x64, 0x99, 0x0d, 0xb6, 0xce,
174 0x98, 0x06, 0xf6, 0x6b, 0x79, 0x70, 0xfd, 0xff, 0x86, 0x17, 0x18, 0x7b, 0xb9, 0xff, 0xfd, 0xff,
175 0x5a, 0xe4, 0xdf, 0x3e, 0xdb, 0xd5, 0xd3, 0x5e, 0x5b, 0x4f, 0x09, 0x02, 0x0d, 0xb0, 0x3e, 0xab,
176 0x1e, 0x03, 0x1d, 0xda, 0x2f, 0xbe, 0x03, 0xd1, 0x79, 0x21, 0x70, 0xa0, 0xf3, 0x00, 0x9c, 0xee,
177 };
178 var out: [64]u8 = undefined;
179 ctr(aes.AesEncryptCtx(aes.Aes128), ctx, out[0..], in[0..], iv, std.builtin.Endian.big);
180 try testing.expectEqualSlices(u8, expected[0..], out[0..]);
181 }
182
183 // Test 9: Large input (> 2*block_length, 100 bytes)
184 {
185 // Create a 100-byte input by extending with zeros
186 var in: [100]u8 = @splat(0);
187 @memcpy(in[0..64], &[_]u8{
188 0x6b, 0xc1, 0xbe, 0xe2, 0x2e, 0x40, 0x9f, 0x96, 0xe9, 0x3d, 0x7e, 0x11, 0x73, 0x93, 0x17, 0x2a,
189 0xae, 0x2d, 0x8a, 0x57, 0x1e, 0x03, 0xac, 0x9c, 0x9e, 0xb7, 0x6f, 0xac, 0x45, 0xaf, 0x8e, 0x51,
190 0x30, 0xc8, 0x1c, 0x46, 0xa3, 0x5c, 0xe4, 0x11, 0xe5, 0xfb, 0xc1, 0x19, 0x1a, 0x0a, 0x52, 0xef,
191 0xf6, 0x9f, 0x24, 0x45, 0xdf, 0x4f, 0x9b, 0x17, 0xad, 0x2b, 0x41, 0x7b, 0xe6, 0x6c, 0x37, 0x10,
192 });
193
194 // Expected output: first 64 bytes from NIST, then CTR continues with zeros
195 var expected: [100]u8 = undefined;
196 @memcpy(expected[0..64], &[_]u8{
197 0x87, 0x4d, 0x61, 0x91, 0xb6, 0x20, 0xe3, 0x26, 0x1b, 0xef, 0x68, 0x64, 0x99, 0x0d, 0xb6, 0xce,
198 0x98, 0x06, 0xf6, 0x6b, 0x79, 0x70, 0xfd, 0xff, 0x86, 0x17, 0x18, 0x7b, 0xb9, 0xff, 0xfd, 0xff,
199 0x5a, 0xe4, 0xdf, 0x3e, 0xdb, 0xd5, 0xd3, 0x5e, 0x5b, 0x4f, 0x09, 0x02, 0x0d, 0xb0, 0x3e, 0xab,
200 0x1e, 0x03, 0x1d, 0xda, 0x2f, 0xbe, 0x03, 0xd1, 0x79, 0x21, 0x70, 0xa0, 0xf3, 0x00, 0x9c, 0xee,
201 });
202 // Compute the rest with zeros XORed with keystream
203 @memcpy(expected[64..], &[_]u8{
204 0xb0, 0x0d, 0x47, 0xf8, 0x14, 0x8a, 0x91, 0x0e, 0xf0, 0x68, 0x30, 0x97, 0x90, 0x4b, 0xa5, 0x02,
205 0x58, 0x99, 0x44, 0x5a, 0x4d, 0xe1, 0x01, 0xf5, 0x13, 0xca, 0xd1, 0x98, 0x7d, 0x89, 0xe9, 0x1b,
206 0x3b, 0xd9, 0xac, 0x79,
207 });
208
209 var out: [100]u8 = undefined;
210 ctr(aes.AesEncryptCtx(aes.Aes128), ctx, out[0..], in[0..], iv, std.builtin.Endian.big);
211 try testing.expectEqualSlices(u8, expected[0..], out[0..]);
212 }
213
214 // Test 10: Test with different endianness (little-endian counter)
215 {
216 const le_iv = [_]u8{ 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 };
217 const in = [_]u8{ 0x00, 0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77, 0x88, 0x99, 0xaa, 0xbb, 0xcc, 0xdd, 0xee, 0xff };
218
219 // We'll compute the expected value from the actual encryption
220 var out: [16]u8 = undefined;
221 ctr(aes.AesEncryptCtx(aes.Aes128), ctx, out[0..], in[0..], le_iv, std.builtin.Endian.little);
222
223 // The actual output for this test with little-endian counter=1
224 const expected = [_]u8{ 0x7e, 0x48, 0x15, 0xa8, 0x16, 0x66, 0xf0, 0xea, 0xad, 0x3c, 0x07, 0x97, 0x2f, 0xe8, 0x25, 0xc1 };
225 try testing.expectEqualSlices(u8, expected[0..], out[0..]);
226 }
227
228 // Make the counter wrap
229 {
230 const iv_top: [16]u8 = @splat(0xff);
231 var buf: [256]u8 = @splat(0);
232 ctr(aes.AesEncryptCtx(aes.Aes128), ctx, buf[0..], buf[0..], iv_top, .little);
233 }
234}