ChaChaNonVecImpl

fn ChaChaNonVecImpl(comptime rounds_nb: usize) type

File

Code

fn ChaChaNonVecImpl(comptime rounds_nb: usize) type {
    return struct {
        const BlockVec = [16]u32;

        fn initContext(key: [8]u32, d: [4]u32) BlockVec {
            const c = "expand 32-byte k";
            const constant_le = comptime [4]u32{
                mem.readInt(u32, c[0..4], .little),
                mem.readInt(u32, c[4..8], .little),
                mem.readInt(u32, c[8..12], .little),
                mem.readInt(u32, c[12..16], .little),
            };
            return BlockVec{
                constant_le[0], constant_le[1], constant_le[2], constant_le[3],
                key[0],         key[1],         key[2],         key[3],
                key[4],         key[5],         key[6],         key[7],
                d[0],           d[1],           d[2],           d[3],
            };
        }

        const QuarterRound = struct {
            a: usize,
            b: usize,
            c: usize,
            d: usize,
        };

        fn Rp(a: usize, b: usize, c: usize, d: usize) QuarterRound {
            return QuarterRound{
                .a = a,
                .b = b,
                .c = c,
                .d = d,
            };
        }

        fn chacha20Core(x: *BlockVec, input: BlockVec) void {
            x.* = input;

            const rounds = comptime [_]QuarterRound{
                Rp(0, 4, 8, 12),
                Rp(1, 5, 9, 13),
                Rp(2, 6, 10, 14),
                Rp(3, 7, 11, 15),
                Rp(0, 5, 10, 15),
                Rp(1, 6, 11, 12),
                Rp(2, 7, 8, 13),
                Rp(3, 4, 9, 14),
            };

            comptime var j: usize = 0;
            inline while (j < rounds_nb) : (j += 2) {
                inline for (rounds) |r| {
                    x[r.a] +%= x[r.b];
                    x[r.d] = math.rotl(u32, x[r.d] ^ x[r.a], @as(u32, 16));
                    x[r.c] +%= x[r.d];
                    x[r.b] = math.rotl(u32, x[r.b] ^ x[r.c], @as(u32, 12));
                    x[r.a] +%= x[r.b];
                    x[r.d] = math.rotl(u32, x[r.d] ^ x[r.a], @as(u32, 8));
                    x[r.c] +%= x[r.d];
                    x[r.b] = math.rotl(u32, x[r.b] ^ x[r.c], @as(u32, 7));
                }
            }
        }

        fn hashToBytes(out: *[64]u8, x: *const BlockVec) void {
            for (0..4) |i| {
                mem.writeInt(u32, out[16 * i + 0 ..][0..4], x[i * 4 + 0], .little);
                mem.writeInt(u32, out[16 * i + 4 ..][0..4], x[i * 4 + 1], .little);
                mem.writeInt(u32, out[16 * i + 8 ..][0..4], x[i * 4 + 2], .little);
                mem.writeInt(u32, out[16 * i + 12 ..][0..4], x[i * 4 + 3], .little);
            }
        }

        fn contextFeedback(x: *BlockVec, ctx: BlockVec) void {
            for (0..16) |i| {
                x[i] +%= ctx[i];
            }
        }

        fn chacha20Xor(out: []u8, in: []const u8, key: [8]u32, nonce_and_counter: [4]u32, comptime count64: bool) void {
            var ctx = initContext(key, nonce_and_counter);
            var x: BlockVec = undefined;
            var buf: [64]u8 = undefined;
            var i: usize = 0;
            while (i + 64 <= in.len) : (i += 64) {
                chacha20Core(x[0..], ctx);
                contextFeedback(&x, ctx);
                hashToBytes(buf[0..], &x);

                var xout = out[i..];
                const xin = in[i..];
                for (0..64) |j| {
                    xout[j] = xin[j];
                }
                for (0..64) |j| {
                    xout[j] ^= buf[j];
                }
                if (count64) {
                    const next = @addWithOverflow(ctx[12], 1);
                    ctx[12] = next[0];
                    ctx[13] +%= next[1];
                } else {
                    ctx[12] +%= 1;
                }
            }
            if (i < in.len) {
                chacha20Core(x[0..], ctx);
                contextFeedback(&x, ctx);
                hashToBytes(buf[0..], &x);

                var xout = out[i..];
                const xin = in[i..];
                for (0..in.len % 64) |j| {
                    xout[j] = xin[j] ^ buf[j];
                }
            }
        }

        fn chacha20Stream(out: []u8, key: [8]u32, nonce_and_counter: [4]u32, comptime count64: bool) void {
            var ctx = initContext(key, nonce_and_counter);
            var x: BlockVec = undefined;
            var i: usize = 0;
            while (i + 64 <= out.len) : (i += 64) {
                chacha20Core(x[0..], ctx);
                contextFeedback(&x, ctx);
                hashToBytes(out[i..][0..64], &x);
                if (count64) {
                    const next = @addWithOverflow(ctx[12], 1);
                    ctx[12] = next[0];
                    ctx[13] +%= next[1];
                } else {
                    ctx[12] +%= 1;
                }
            }
            if (i < out.len) {
                chacha20Core(x[0..], ctx);
                contextFeedback(&x, ctx);

                var buf: [64]u8 = undefined;
                hashToBytes(buf[0..], &x);
                @memcpy(out[i..], buf[0 .. out.len - i]);
            }
        }

        fn hchacha20(input: [16]u8, key: [32]u8) [32]u8 {
            var c: [4]u32 = undefined;
            for (c, 0..) |_, i| {
                c[i] = mem.readInt(u32, input[4 * i ..][0..4], .little);
            }
            const ctx = initContext(keyToWords(key), c);
            var x: BlockVec = undefined;
            chacha20Core(x[0..], ctx);
            var out: [32]u8 = undefined;
            mem.writeInt(u32, out[0..4], x[0], .little);
            mem.writeInt(u32, out[4..8], x[1], .little);
            mem.writeInt(u32, out[8..12], x[2], .little);
            mem.writeInt(u32, out[12..16], x[3], .little);
            mem.writeInt(u32, out[16..20], x[12], .little);
            mem.writeInt(u32, out[20..24], x[13], .little);
            mem.writeInt(u32, out[24..28], x[14], .little);
            mem.writeInt(u32, out[28..32], x[15], .little);
            return out;
        }
    };
}