const std = @import("std");
const mem = std.mem;
const Random = std.rand.Random;
const Self = @This();
const Cipher = std.crypto.stream.chacha.ChaCha8IETF;
const State = [2 * Cipher.block_length]u8;
state: State,
offset: usize,
const nonce = [_]u8{0} ** Cipher.nonce_length;
pub const secret_seed_length = Cipher.key_length;
pub fn init(secret_seed: [secret_seed_length]u8) Self {
var self = Self{ .state = undefined, .offset = 0 };
Cipher.stream(&self.state, 0, secret_seed, nonce);
return self;
}
pub fn addEntropy(self: *Self, bytes: []const u8) void {
var i: usize = 0;
while (i + Cipher.key_length <= bytes.len) : (i += Cipher.key_length) {
Cipher.xor(
self.state[0..Cipher.key_length],
self.state[0..Cipher.key_length],
0,
bytes[i..][0..Cipher.key_length].*,
nonce,
);
}
if (i < bytes.len) {
var k = [_]u8{0} ** Cipher.key_length;
mem.copy(u8, k[0..], bytes[i..]);
Cipher.xor(
self.state[0..Cipher.key_length],
self.state[0..Cipher.key_length],
0,
k,
nonce,
);
}
self.refill();
}
pub fn random(self: *Self) Random {
return Random.init(self, fill);
}
fn refill(self: *Self) void {
Cipher.stream(&self.state, 0, self.state[0..Cipher.key_length].*, nonce);
self.offset = 0;
}
pub fn fill(self: *Self, buf_: []u8) void {
const bytes = self.state[Cipher.key_length..];
var buf = buf_;
const avail = bytes.len - self.offset;
if (avail > 0) {
const n = @min(avail, buf.len);
mem.copy(u8, buf[0..n], bytes[self.offset..][0..n]);
mem.set(u8, bytes[self.offset..][0..n], 0);
buf = buf[n..];
self.offset += n;
}
if (buf.len == 0) return;
self.refill();
while (buf.len >= bytes.len) {
mem.copy(u8, buf[0..bytes.len], bytes);
buf = buf[bytes.len..];
self.refill();
}
if (buf.len > 0) {
mem.copy(u8, buf, bytes[0..buf.len]);
mem.set(u8, bytes[0..buf.len], 0);
self.offset = buf.len;
}
}