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const std = @import("std");
const assert = std.debug.assert;
const crypto = std.crypto;
const debug = std.debug;
const Ghash = std.crypto.onetimeauth.Ghash;
const math = std.math;
const mem = std.mem;
const modes = crypto.core.modes;
const AuthenticationError = crypto.errors.AuthenticationError;
pub const Aes128Gcm = AesGcm(crypto.core.aes.Aes128);
pub const Aes256Gcm = AesGcm(crypto.core.aes.Aes256);
fn AesGcm(comptime Aes: anytype) type {
debug.assert(Aes.block.block_length == 16);
return struct {
pub const tag_length = 16;
pub const nonce_length = 12;
pub const key_length = Aes.key_bits / 8;
const zeros = [_]u8{0} ** 16;
/// `c`: The ciphertext buffer to write the encrypted data to.
/// `tag`: The authentication tag buffer to write the computed tag to.
/// `m`: The plaintext message to encrypt.
/// `ad`: The associated data to authenticate.
/// `npub`: The nonce to use for encryption.
/// `key`: The encryption key.
pub fn encrypt(c: []u8, tag: *[tag_length]u8, m: []const u8, ad: []const u8, npub: [nonce_length]u8, key: [key_length]u8) void {
debug.assert(c.len == m.len);
debug.assert(m.len <= 16 * ((1 << 32) - 2));
const aes = Aes.initEnc(key);
var h: [16]u8 = undefined;
aes.encrypt(&h, &zeros);
var t: [16]u8 = undefined;
var j: [16]u8 = undefined;
j[0..nonce_length].* = npub;
mem.writeInt(u32, j[nonce_length..][0..4], 1, .big);
aes.encrypt(&t, &j);
const block_count = (math.divCeil(usize, ad.len, Ghash.block_length) catch unreachable) + (math.divCeil(usize, c.len, Ghash.block_length) catch unreachable) + 1;
var mac = Ghash.initForBlockCount(&h, block_count);
mac.update(ad);
mac.pad();
mem.writeInt(u32, j[nonce_length..][0..4], 2, .big);
modes.ctr(@TypeOf(aes), aes, c, m, j, .big);
mac.update(c[0..m.len][0..]);
mac.pad();
var final_block = h;
mem.writeInt(u64, final_block[0..8], @as(u64, ad.len) * 8, .big);
mem.writeInt(u64, final_block[8..16], @as(u64, m.len) * 8, .big);
mac.update(&final_block);
mac.final(tag);
for (t, 0..) |x, i| {
tag[i] ^= x;
}
}
/// `m`: Message
/// `c`: Ciphertext
/// `tag`: Authentication tag
/// `ad`: Associated data
/// `npub`: Public nonce
/// `k`: Private key
/// Asserts `c.len == m.len`.
///
/// Contents of `m` are undefined if an error is returned.
pub fn decrypt(m: []u8, c: []const u8, tag: [tag_length]u8, ad: []const u8, npub: [nonce_length]u8, key: [key_length]u8) AuthenticationError!void {
assert(c.len == m.len);
const aes = Aes.initEnc(key);
var h: [16]u8 = undefined;
aes.encrypt(&h, &zeros);
var t: [16]u8 = undefined;
var j: [16]u8 = undefined;
j[0..nonce_length].* = npub;
mem.writeInt(u32, j[nonce_length..][0..4], 1, .big);
aes.encrypt(&t, &j);
const block_count = (math.divCeil(usize, ad.len, Ghash.block_length) catch unreachable) + (math.divCeil(usize, c.len, Ghash.block_length) catch unreachable) + 1;
var mac = Ghash.initForBlockCount(&h, block_count);
mac.update(ad);
mac.pad();
mac.update(c);
mac.pad();
var final_block = h;
mem.writeInt(u64, final_block[0..8], @as(u64, ad.len) * 8, .big);
mem.writeInt(u64, final_block[8..16], @as(u64, m.len) * 8, .big);
mac.update(&final_block);
var computed_tag: [Ghash.mac_length]u8 = undefined;
mac.final(&computed_tag);
for (t, 0..) |x, i| {
computed_tag[i] ^= x;
}
const verify = crypto.timing_safe.eql([tag_length]u8, computed_tag, tag);
if (!verify) {
crypto.secureZero(u8, &computed_tag);
@memset(m, undefined);
return error.AuthenticationFailed;
}
mem.writeInt(u32, j[nonce_length..][0..4], 2, .big);
modes.ctr(@TypeOf(aes), aes, m, c, j, .big);
}
};
}
const htest = @import("test.zig");
const testing = std.testing;
test "Aes256Gcm - Empty message and no associated data" {
const key: [Aes256Gcm.key_length]u8 = [_]u8{0x69} ** Aes256Gcm.key_length;
const nonce: [Aes256Gcm.nonce_length]u8 = [_]u8{0x42} ** Aes256Gcm.nonce_length;
const ad = "";
const m = "";
var c: [m.len]u8 = undefined;
var tag: [Aes256Gcm.tag_length]u8 = undefined;
Aes256Gcm.encrypt(&c, &tag, m, ad, nonce, key);
try htest.assertEqual("6b6ff610a16fa4cd59f1fb7903154e92", &tag);
}
test "Aes256Gcm - Associated data only" {
const key: [Aes256Gcm.key_length]u8 = [_]u8{0x69} ** Aes256Gcm.key_length;
const nonce: [Aes256Gcm.nonce_length]u8 = [_]u8{0x42} ** Aes256Gcm.nonce_length;
const m = "";
const ad = "Test with associated data";
var c: [m.len]u8 = undefined;
var tag: [Aes256Gcm.tag_length]u8 = undefined;
Aes256Gcm.encrypt(&c, &tag, m, ad, nonce, key);
try htest.assertEqual("262ed164c2dfb26e080a9d108dd9dd4c", &tag);
}
test "Aes256Gcm - Message only" {
const key: [Aes256Gcm.key_length]u8 = [_]u8{0x69} ** Aes256Gcm.key_length;
const nonce: [Aes256Gcm.nonce_length]u8 = [_]u8{0x42} ** Aes256Gcm.nonce_length;
const m = "Test with message only";
const ad = "";
var c: [m.len]u8 = undefined;
var m2: [m.len]u8 = undefined;
var tag: [Aes256Gcm.tag_length]u8 = undefined;
Aes256Gcm.encrypt(&c, &tag, m, ad, nonce, key);
try Aes256Gcm.decrypt(&m2, &c, tag, ad, nonce, key);
try testing.expectEqualSlices(u8, m[0..], m2[0..]);
try htest.assertEqual("5ca1642d90009fea33d01f78cf6eefaf01d539472f7c", &c);
try htest.assertEqual("07cd7fc9103e2f9e9bf2dfaa319caff4", &tag);
}
test "Aes256Gcm - Message and associated data" {
const key: [Aes256Gcm.key_length]u8 = [_]u8{0x69} ** Aes256Gcm.key_length;
const nonce: [Aes256Gcm.nonce_length]u8 = [_]u8{0x42} ** Aes256Gcm.nonce_length;
const m = "Test with message";
const ad = "Test with associated data";
var c: [m.len]u8 = undefined;
var m2: [m.len]u8 = undefined;
var tag: [Aes256Gcm.tag_length]u8 = undefined;
Aes256Gcm.encrypt(&c, &tag, m, ad, nonce, key);
try Aes256Gcm.decrypt(&m2, &c, tag, ad, nonce, key);
try testing.expectEqualSlices(u8, m[0..], m2[0..]);
try htest.assertEqual("5ca1642d90009fea33d01f78cf6eefaf01", &c);
try htest.assertEqual("64accec679d444e2373bd9f6796c0d2c", &tag);
}
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