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2e4b409f31
* get rid of the pointless fences * make seed_len 16 instead of 32, which is accurate since it was already padding the rest anyway; now we do 1 pad instead of 2. * secureZero to clear the AT_RANDOM auxval * add a flag root source files can use to disable the start code. This is in case people want to opt out of the initialization when they don't depend on it.
63 lines
2.5 KiB
Zig
63 lines
2.5 KiB
Zig
// SPDX-License-Identifier: MIT
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// Copyright (c) 2015-2020 Zig Contributors
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// This file is part of [zig](https://ziglang.org/), which is MIT licensed.
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// The MIT license requires this copyright notice to be included in all copies
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// and substantial portions of the software.
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//! Thread-local cryptographically secure pseudo-random number generator.
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//! This file has public declarations that are intended to be used internally
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//! by the standard library; this namespace is not intended to be exposed
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//! directly to standard library users.
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const std = @import("std");
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const root = @import("root");
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const mem = std.mem;
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/// We use this as a layer of indirection because global const pointers cannot
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/// point to thread-local variables.
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pub var interface = std.rand.Random{ .fillFn = tlsCsprngFill };
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pub threadlocal var csprng_state: std.crypto.core.Gimli = undefined;
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pub threadlocal var csprng_state_initialized = false;
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fn tlsCsprngFill(r: *const std.rand.Random, buf: []u8) void {
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if (std.builtin.link_libc and @hasDecl(std.c, "arc4random_buf")) {
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// arc4random is already a thread-local CSPRNG.
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return std.c.arc4random_buf(buf.ptr, buf.len);
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}
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if (!csprng_state_initialized) {
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var seed: [seed_len]u8 = undefined;
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// Because we panic on getrandom() failing, we provide the opportunity
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// to override the default seed function. This also makes
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// `std.crypto.random` available on freestanding targets, provided that
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// the `cryptoRandomSeed` function is provided.
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if (@hasDecl(root, "cryptoRandomSeed")) {
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root.cryptoRandomSeed(&seed);
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} else {
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defaultSeed(&seed);
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}
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init(seed);
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}
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if (buf.len != 0) {
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csprng_state.squeeze(buf);
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} else {
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csprng_state.permute();
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}
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mem.set(u8, csprng_state.toSlice()[0..std.crypto.core.Gimli.RATE], 0);
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}
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fn defaultSeed(buffer: *[seed_len]u8) void {
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std.os.getrandom(buffer) catch @panic("getrandom() failed to seed thread-local CSPRNG");
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}
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pub const seed_len = 16;
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pub fn init(seed: [seed_len]u8) void {
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var initial_state: [std.crypto.core.Gimli.BLOCKBYTES]u8 = undefined;
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mem.copy(u8, initial_state[0..seed_len], &seed);
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mem.set(u8, initial_state[seed_len..], 0);
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csprng_state = std.crypto.core.Gimli.init(initial_state);
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// This is at the end so that accidental recursive dependencies result
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// in stack overflows instead of invalid random data.
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csprng_state_initialized = true;
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}
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