tiny.quic.crypto.header

1const std = @import("std");2const quic = @import("../root.zig");34const crypto = quic.crypto;5const Aes128 = std.crypto.core.aes.Aes128;6const ChaCha20 = std.crypto.stream.chacha.ChaCha20IETF;78pub const sample_bytes: usize = 16;9pub const mask_bytes: usize = 5;1011pub const ApplyError = error{12    InvalidPacketNumberLength,13    InvalidPacketNumberOffset,14    TruncatedPacket,15};1617pub const Inspected = struct {18    first_byte: u8,19    pn_len: u3,20};2122pub fn mask(keys: *const crypto.Keys, sample: *const [sample_bytes]u8) [mask_bytes]u8 {23    return switch (keys.selectedSuite()) {24        .aes_128_gcm_sha256 => aesMask(keys, sample),25        .chacha20_poly1305_sha256 => chachaMask(keys, sample),26    };27}2829fn aesMask(keys: *const crypto.Keys, sample: *const [sample_bytes]u8) [mask_bytes]u8 {30    const header_key = keys.headerKey();31    const hp_key: [16]u8 = header_key[0..16].*;32    const cipher = Aes128.initEnc(hp_key);33    var block: [sample_bytes]u8 = undefined;34    cipher.encrypt(&block, sample);35    return block[0..mask_bytes].*;36}3738fn chachaMask(keys: *const crypto.Keys, sample: *const [sample_bytes]u8) [mask_bytes]u8 {39    const counter = std.mem.readInt(u32, sample[0..4], .little);40    const nonce: [12]u8 = sample[4..16].*;41    var zeros: [mask_bytes]u8 = @splat(0);42    var result: [mask_bytes]u8 = undefined;43    ChaCha20.xor(&result, &zeros, counter, keys.headerKey(), nonce);44    return result;45}4647fn protectedBits(first: u8) u8 {48    return if (first & 0x80 != 0) 0x0f else 0x1f;49}5051fn validate(packet: []const u8, pn_offset: usize, pn_len: u3) ApplyError!void {52    if (packet.len == 0) return error.TruncatedPacket;53    if (pn_offset == 0) return error.InvalidPacketNumberOffset;54    if (pn_len == 0 or pn_len > 4) return error.InvalidPacketNumberLength;55    if (pn_offset > packet.len) return error.TruncatedPacket;56    if (pn_len > packet.len - pn_offset) return error.TruncatedPacket;57}5859pub fn inspect(60    protection_mask: [mask_bytes]u8,61    packet: []const u8,62    pn_offset: usize,63) ApplyError!Inspected {64    if (packet.len == 0) return error.TruncatedPacket;65    if (pn_offset == 0) return error.InvalidPacketNumberOffset;66    const first = packet[0] ^ (protection_mask[0] & protectedBits(packet[0]));67    const pn_len = quic.packet.packetNumberLength(first);68    try validate(packet, pn_offset, pn_len);69    return .{ .first_byte = first, .pn_len = pn_len };70}7172pub fn protect(73    protection_mask: [mask_bytes]u8,74    packet: []u8,75    pn_offset: usize,76    pn_len: u3,77) ApplyError!void {78    try validate(packet, pn_offset, pn_len);79    packet[0] ^= protection_mask[0] & protectedBits(packet[0]);80    for (0..4) |index| {81        if (index >= pn_len) break;82        packet[pn_offset + index] ^= protection_mask[index + 1];83    }84}8586pub fn unprotect(87    protection_mask: [mask_bytes]u8,88    packet: []u8,89    pn_offset: usize,90) ApplyError!u3 {91    const inspected = try inspect(protection_mask, packet, pn_offset);92    packet[0] = inspected.first_byte;93    for (0..4) |index| {94        if (index >= inspected.pn_len) break;95        packet[pn_offset + index] ^= protection_mask[index + 1];96    }97    return inspected.pn_len;98}

1pub const header = @import("header.zig");