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d29871977f
We already have a LICENSE file that covers the Zig Standard Library. We no longer need to remind everyone that the license is MIT in every single file. Previously this was introduced to clarify the situation for a fork of Zig that made Zig's LICENSE file harder to find, and replaced it with their own license that required annual payments to their company. However that fork now appears to be dead. So there is no need to reinforce the copyright notice in every single file.
47 lines
2.2 KiB
Zig
47 lines
2.2 KiB
Zig
// Based on Go stdlib implementation
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const std = @import("../std.zig");
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const builtin = std.builtin;
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const mem = std.mem;
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const debug = std.debug;
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/// Counter mode.
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///
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/// This mode creates a key stream by encrypting an incrementing counter using a block cipher, and adding it to the source material.
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///
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/// Important: the counter mode doesn't provide authenticated encryption: the ciphertext can be trivially modified without this being detected.
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/// As a result, applications should generally never use it directly, but only in a construction that includes a MAC.
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pub fn ctr(comptime BlockCipher: anytype, block_cipher: BlockCipher, dst: []u8, src: []const u8, iv: [BlockCipher.block_length]u8, endian: builtin.Endian) void {
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debug.assert(dst.len >= src.len);
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const block_length = BlockCipher.block_length;
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var counter: [BlockCipher.block_length]u8 = undefined;
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var counterInt = mem.readInt(u128, &iv, endian);
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var i: usize = 0;
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const parallel_count = BlockCipher.block.parallel.optimal_parallel_blocks;
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const wide_block_length = parallel_count * 16;
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if (src.len >= wide_block_length) {
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var counters: [parallel_count * 16]u8 = undefined;
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while (i + wide_block_length <= src.len) : (i += wide_block_length) {
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comptime var j = 0;
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inline while (j < parallel_count) : (j += 1) {
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mem.writeInt(u128, counters[j * 16 .. j * 16 + 16], counterInt, endian);
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counterInt +%= 1;
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}
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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);
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}
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}
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while (i + block_length <= src.len) : (i += block_length) {
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mem.writeInt(u128, &counter, counterInt, endian);
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counterInt +%= 1;
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block_cipher.xor(dst[i .. i + block_length][0..block_length], src[i .. i + block_length][0..block_length], counter);
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}
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if (i < src.len) {
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mem.writeInt(u128, &counter, counterInt, endian);
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var pad = [_]u8{0} ** block_length;
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mem.copy(u8, &pad, src[i..]);
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block_cipher.xor(&pad, &pad, counter);
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mem.copy(u8, dst[i..], pad[0 .. src.len - i]);
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}
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}
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