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const std = @import("../std.zig");
const mem = std.mem;
const mulWide = std.math.mulWide;
pub const Poly1305 = struct {
pub const block_length: usize = 16;
pub const mac_length = 16;
pub const key_length = 32;
// constant multiplier (from the secret key)
r: [2]u64,
// accumulated hash
h: [3]u64 = [_]u64{ 0, 0, 0 },
// random number added at the end (from the secret key)
end_pad: [2]u64,
// how many bytes are waiting to be processed in a partial block
leftover: usize = 0,
// partial block buffer
buf: [block_length]u8 align(16) = undefined,
pub fn init(key: *const [key_length]u8) Poly1305 {
return Poly1305{
.r = [_]u64{
mem.readInt(u64, key[0..8], .little) & 0x0ffffffc0fffffff,
mem.readInt(u64, key[8..16], .little) & 0x0ffffffc0ffffffc,
},
.end_pad = [_]u64{
mem.readInt(u64, key[16..24], .little),
mem.readInt(u64, key[24..32], .little),
},
};
}
fn add(a: u64, b: u64, c: u1) struct { u64, u1 } {
const v1 = @addWithOverflow(a, b);
const v2 = @addWithOverflow(v1[0], c);
return .{ v2[0], v1[1] | v2[1] };
}
fn sub(a: u64, b: u64, c: u1) struct { u64, u1 } {
const v1 = @subWithOverflow(a, b);
const v2 = @subWithOverflow(v1[0], c);
return .{ v2[0], v1[1] | v2[1] };
}
fn blocks(st: *Poly1305, m: []const u8, comptime last: bool) void {
const hibit: u64 = if (last) 0 else 1;
const r0 = st.r[0];
const r1 = st.r[1];
var h0 = st.h[0];
var h1 = st.h[1];
var h2 = st.h[2];
var i: usize = 0;
while (i + block_length <= m.len) : (i += block_length) {
const in0 = mem.readInt(u64, m[i..][0..8], .little);
const in1 = mem.readInt(u64, m[i + 8 ..][0..8], .little);
// Add the input message to H
var v = @addWithOverflow(h0, in0);
h0 = v[0];
v = add(h1, in1, v[1]);
h1 = v[0];
h2 +%= v[1] +% hibit;
// Compute H * R
const m0 = mulWide(u64, h0, r0);
const h1r0 = mulWide(u64, h1, r0);
const h0r1 = mulWide(u64, h0, r1);
const h2r0 = mulWide(u64, h2, r0);
const h1r1 = mulWide(u64, h1, r1);
const m3 = mulWide(u64, h2, r1);
const m1 = h1r0 +% h0r1;
const m2 = h2r0 +% h1r1;
const t0 = @as(u64, @truncate(m0));
v = @addWithOverflow(@as(u64, @truncate(m1)), @as(u64, @truncate(m0 >> 64)));
const t1 = v[0];
v = add(@as(u64, @truncate(m2)), @as(u64, @truncate(m1 >> 64)), v[1]);
const t2 = v[0];
v = add(@as(u64, @truncate(m3)), @as(u64, @truncate(m2 >> 64)), v[1]);
const t3 = v[0];
// Partial reduction
h0 = t0;
h1 = t1;
h2 = t2 & 3;
// Add c*(4+1)
const cclo = t2 & ~@as(u64, 3);
const cchi = t3;
v = @addWithOverflow(h0, cclo);
h0 = v[0];
v = add(h1, cchi, v[1]);
h1 = v[0];
h2 +%= v[1];
const cc = (cclo | (@as(u128, cchi) << 64)) >> 2;
v = @addWithOverflow(h0, @as(u64, @truncate(cc)));
h0 = v[0];
v = add(h1, @as(u64, @truncate(cc >> 64)), v[1]);
h1 = v[0];
h2 +%= v[1];
}
st.h = [_]u64{ h0, h1, h2 };
}
pub fn update(st: *Poly1305, m: []const u8) void {
var mb = m;
// handle leftover
if (st.leftover > 0) {
const want = @min(block_length - st.leftover, mb.len);
const mc = mb[0..want];
for (mc, 0..) |x, i| {
st.buf[st.leftover + i] = x;
}
mb = mb[want..];
st.leftover += want;
if (st.leftover < block_length) {
return;
}
st.blocks(&st.buf, false);
st.leftover = 0;
}
// process full blocks
if (mb.len >= block_length) {
const want = mb.len & ~(block_length - 1);
st.blocks(mb[0..want], false);
mb = mb[want..];
}
// store leftover
if (mb.len > 0) {
for (mb, 0..) |x, i| {
st.buf[st.leftover + i] = x;
}
st.leftover += mb.len;
}
}
/// Zero-pad to align the next input to the first byte of a block
pub fn pad(st: *Poly1305) void {
if (st.leftover == 0) {
return;
}
@memset(st.buf[st.leftover..], 0);
st.blocks(&st.buf, false);
st.leftover = 0;
}
pub fn final(st: *Poly1305, out: *[mac_length]u8) void {
if (st.leftover > 0) {
var i = st.leftover;
st.buf[i] = 1;
i += 1;
@memset(st.buf[i..], 0);
st.blocks(&st.buf, true);
}
var h0 = st.h[0];
var h1 = st.h[1];
const h2 = st.h[2];
// H - (2^130 - 5)
var v = @subWithOverflow(h0, 0xfffffffffffffffb);
const h_p0 = v[0];
v = sub(h1, 0xffffffffffffffff, v[1]);
const h_p1 = v[0];
v = sub(h2, 0x0000000000000003, v[1]);
// Final reduction, subtract 2^130-5 from H if H >= 2^130-5
const mask = @as(u64, v[1]) -% 1;
h0 ^= mask & (h0 ^ h_p0);
h1 ^= mask & (h1 ^ h_p1);
// Add the first half of the key, we intentionally don't use @addWithOverflow() here.
st.h[0] = h0 +% st.end_pad[0];
const c = ((h0 & st.end_pad[0]) | ((h0 | st.end_pad[0]) & ~st.h[0])) >> 63;
st.h[1] = h1 +% st.end_pad[1] +% c;
mem.writeInt(u64, out[0..8], st.h[0], .little);
mem.writeInt(u64, out[8..16], st.h[1], .little);
std.crypto.secureZero(u8, @as([*]u8, @ptrCast(st))[0..@sizeOf(Poly1305)]);
}
pub fn create(out: *[mac_length]u8, msg: []const u8, key: *const [key_length]u8) void {
var st = Poly1305.init(key);
st.update(msg);
st.final(out);
}
};
test "rfc7439 vector1" {
const expected_mac = "\xa8\x06\x1d\xc1\x30\x51\x36\xc6\xc2\x2b\x8b\xaf\x0c\x01\x27\xa9";
const msg = "Cryptographic Forum Research Group";
const key = "\x85\xd6\xbe\x78\x57\x55\x6d\x33\x7f\x44\x52\xfe\x42\xd5\x06\xa8" ++
"\x01\x03\x80\x8a\xfb\x0d\xb2\xfd\x4a\xbf\xf6\xaf\x41\x49\xf5\x1b";
var mac: [16]u8 = undefined;
Poly1305.create(mac[0..], msg, key);
try std.testing.expectEqualSlices(u8, expected_mac, &mac);
}
test "requiring a final reduction" {
const expected_mac = [_]u8{ 25, 13, 249, 42, 164, 57, 99, 60, 149, 181, 74, 74, 13, 63, 121, 6 };
const msg = [_]u8{ 253, 193, 249, 146, 70, 6, 214, 226, 131, 213, 241, 116, 20, 24, 210, 224, 65, 151, 255, 104, 133 };
const key = [_]u8{ 190, 63, 95, 57, 155, 103, 77, 170, 7, 98, 106, 44, 117, 186, 90, 185, 109, 118, 184, 24, 69, 41, 166, 243, 119, 132, 151, 61, 52, 43, 64, 250 };
var mac: [16]u8 = undefined;
Poly1305.create(mac[0..], &msg, &key);
try std.testing.expectEqualSlices(u8, &expected_mac, &mac);
}
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