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zig/lib/std/crypto/aes_ocb.zig
Andrew Kelley d29871977f remove redundant license headers from zig standard library 
We already have a LICENSE file that covers the Zig Standard Library. We
no longer need to remind everyone that the license is MIT in every single
file.

Previously this was introduced to clarify the situation for a fork of
Zig that made Zig's LICENSE file harder to find, and replaced it with
their own license that required annual payments to their company.
However that fork now appears to be dead. So there is no need to
reinforce the copyright notice in every single file.
2021-08-24 12:25:09 -07:00

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const std = @import("std");
const crypto = std.crypto;
const aes = crypto.core.aes;
const assert = std.debug.assert;
const math = std.math;
const mem = std.mem;
const AuthenticationError = crypto.errors.AuthenticationError;
pub const Aes128Ocb = AesOcb(aes.Aes128);
pub const Aes256Ocb = AesOcb(aes.Aes256);
const Block = [16]u8;
/// AES-OCB (RFC 7253 - https://competitions.cr.yp.to/round3/ocbv11.pdf)
fn AesOcb(comptime Aes: anytype) type {
const EncryptCtx = aes.AesEncryptCtx(Aes);
const DecryptCtx = aes.AesDecryptCtx(Aes);
return struct {
pub const key_length = Aes.key_bits / 8;
pub const nonce_length: usize = 12;
pub const tag_length: usize = 16;
const Lx = struct {
star: Block align(16),
dol: Block align(16),
table: [56]Block align(16) = undefined,
upto: usize,
inline fn double(l: Block) Block {
const l_ = mem.readIntBig(u128, &l);
const l_2 = (l_ << 1) ^ (0x87 & -%(l_ >> 127));
var l2: Block = undefined;
mem.writeIntBig(u128, &l2, l_2);
return l2;
}
fn precomp(lx: *Lx, upto: usize) []const Block {
const table = &lx.table;
assert(upto < table.len);
var i = lx.upto;
while (i + 1 <= upto) : (i += 1) {
table[i + 1] = double(table[i]);
}
lx.upto = upto;
return lx.table[0 .. upto + 1];
}
fn init(aes_enc_ctx: EncryptCtx) Lx {
const zeros = [_]u8{0} ** 16;
var star: Block = undefined;
aes_enc_ctx.encrypt(&star, &zeros);
const dol = double(star);
var lx = Lx{ .star = star, .dol = dol, .upto = 0 };
lx.table[0] = double(dol);
return lx;
}
};
fn hash(aes_enc_ctx: EncryptCtx, lx: *Lx, a: []const u8) Block {
const full_blocks: usize = a.len / 16;
const x_max = if (full_blocks > 0) math.log2_int(usize, full_blocks) else 0;
const lt = lx.precomp(x_max);
var sum = [_]u8{0} ** 16;
var offset = [_]u8{0} ** 16;
var i: usize = 0;
while (i < full_blocks) : (i += 1) {
xorWith(&offset, lt[@ctz(usize, i + 1)]);
var e = xorBlocks(offset, a[i * 16 ..][0..16].*);
aes_enc_ctx.encrypt(&e, &e);
xorWith(&sum, e);
}
const leftover = a.len % 16;
if (leftover > 0) {
xorWith(&offset, lx.star);
var padded = [_]u8{0} ** 16;
mem.copy(u8, padded[0..leftover], a[i * 16 ..][0..leftover]);
padded[leftover] = 1;
var e = xorBlocks(offset, padded);
aes_enc_ctx.encrypt(&e, &e);
xorWith(&sum, e);
}
return sum;
}
fn getOffset(aes_enc_ctx: EncryptCtx, npub: [nonce_length]u8) Block {
var nx = [_]u8{0} ** 16;
nx[0] = @intCast(u8, @truncate(u7, tag_length * 8) << 1);
nx[16 - nonce_length - 1] = 1;
mem.copy(u8, nx[16 - nonce_length ..], &npub);
const bottom = @truncate(u6, nx[15]);
nx[15] &= 0xc0;
var ktop_: Block = undefined;
aes_enc_ctx.encrypt(&ktop_, &nx);
const ktop = mem.readIntBig(u128, &ktop_);
var stretch = (@as(u192, ktop) << 64) | @as(u192, @truncate(u64, ktop >> 64) ^ @truncate(u64, ktop >> 56));
var offset: Block = undefined;
mem.writeIntBig(u128, &offset, @truncate(u128, stretch >> (64 - @as(u7, bottom))));
return offset;
}
const has_aesni = std.Target.x86.featureSetHas(std.Target.current.cpu.features, .aes);
const has_armaes = std.Target.aarch64.featureSetHas(std.Target.current.cpu.features, .aes);
const wb: usize = if ((std.Target.current.cpu.arch == .x86_64 and has_aesni) or (std.Target.current.cpu.arch == .aarch64 and has_armaes)) 4 else 0;
/// c: ciphertext: output buffer should be of size m.len
/// tag: authentication tag: output MAC
/// m: message
/// ad: Associated Data
/// npub: public nonce
/// k: secret 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 {
assert(c.len == m.len);
const aes_enc_ctx = Aes.initEnc(key);
const full_blocks: usize = m.len / 16;
const x_max = if (full_blocks > 0) math.log2_int(usize, full_blocks) else 0;
var lx = Lx.init(aes_enc_ctx);
const lt = lx.precomp(x_max);
var offset = getOffset(aes_enc_ctx, npub);
var sum = [_]u8{0} ** 16;
var i: usize = 0;
while (wb > 0 and i + wb <= full_blocks) : (i += wb) {
var offsets: [wb]Block align(16) = undefined;
var es: [16 * wb]u8 align(16) = undefined;
var j: usize = 0;
while (j < wb) : (j += 1) {
xorWith(&offset, lt[@ctz(usize, i + 1 + j)]);
offsets[j] = offset;
const p = m[(i + j) * 16 ..][0..16].*;
mem.copy(u8, es[j * 16 ..][0..16], &xorBlocks(p, offsets[j]));
xorWith(&sum, p);
}
aes_enc_ctx.encryptWide(wb, &es, &es);
j = 0;
while (j < wb) : (j += 1) {
const e = es[j * 16 ..][0..16].*;
mem.copy(u8, c[(i + j) * 16 ..][0..16], &xorBlocks(e, offsets[j]));
}
}
while (i < full_blocks) : (i += 1) {
xorWith(&offset, lt[@ctz(usize, i + 1)]);
const p = m[i * 16 ..][0..16].*;
var e = xorBlocks(p, offset);
aes_enc_ctx.encrypt(&e, &e);
mem.copy(u8, c[i * 16 ..][0..16], &xorBlocks(e, offset));
xorWith(&sum, p);
}
const leftover = m.len % 16;
if (leftover > 0) {
xorWith(&offset, lx.star);
var pad = offset;
aes_enc_ctx.encrypt(&pad, &pad);
for (m[i * 16 ..]) |x, j| {
c[i * 16 + j] = pad[j] ^ x;
}
var e = [_]u8{0} ** 16;
mem.copy(u8, e[0..leftover], m[i * 16 ..][0..leftover]);
e[leftover] = 0x80;
xorWith(&sum, e);
}
var e = xorBlocks(xorBlocks(sum, offset), lx.dol);
aes_enc_ctx.encrypt(&e, &e);
tag.* = xorBlocks(e, hash(aes_enc_ctx, &lx, ad));
}
/// m: message: output buffer should be of size c.len
/// c: ciphertext
/// tag: authentication tag
/// ad: Associated Data
/// npub: public nonce
/// k: secret key
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_enc_ctx = Aes.initEnc(key);
const aes_dec_ctx = DecryptCtx.initFromEnc(aes_enc_ctx);
const full_blocks: usize = m.len / 16;
const x_max = if (full_blocks > 0) math.log2_int(usize, full_blocks) else 0;
var lx = Lx.init(aes_enc_ctx);
const lt = lx.precomp(x_max);
var offset = getOffset(aes_enc_ctx, npub);
var sum = [_]u8{0} ** 16;
var i: usize = 0;
while (wb > 0 and i + wb <= full_blocks) : (i += wb) {
var offsets: [wb]Block align(16) = undefined;
var es: [16 * wb]u8 align(16) = undefined;
var j: usize = 0;
while (j < wb) : (j += 1) {
xorWith(&offset, lt[@ctz(usize, i + 1 + j)]);
offsets[j] = offset;
const q = c[(i + j) * 16 ..][0..16].*;
mem.copy(u8, es[j * 16 ..][0..16], &xorBlocks(q, offsets[j]));
}
aes_dec_ctx.decryptWide(wb, &es, &es);
j = 0;
while (j < wb) : (j += 1) {
const p = xorBlocks(es[j * 16 ..][0..16].*, offsets[j]);
mem.copy(u8, m[(i + j) * 16 ..][0..16], &p);
xorWith(&sum, p);
}
}
while (i < full_blocks) : (i += 1) {
xorWith(&offset, lt[@ctz(usize, i + 1)]);
const q = c[i * 16 ..][0..16].*;
var e = xorBlocks(q, offset);
aes_dec_ctx.decrypt(&e, &e);
const p = xorBlocks(e, offset);
mem.copy(u8, m[i * 16 ..][0..16], &p);
xorWith(&sum, p);
}
const leftover = m.len % 16;
if (leftover > 0) {
xorWith(&offset, lx.star);
var pad = offset;
aes_enc_ctx.encrypt(&pad, &pad);
for (c[i * 16 ..]) |x, j| {
m[i * 16 + j] = pad[j] ^ x;
}
var e = [_]u8{0} ** 16;
mem.copy(u8, e[0..leftover], m[i * 16 ..][0..leftover]);
e[leftover] = 0x80;
xorWith(&sum, e);
}
var e = xorBlocks(xorBlocks(sum, offset), lx.dol);
aes_enc_ctx.encrypt(&e, &e);
var computed_tag = xorBlocks(e, hash(aes_enc_ctx, &lx, ad));
const verify = crypto.utils.timingSafeEql([tag_length]u8, computed_tag, tag);
crypto.utils.secureZero(u8, &computed_tag);
if (!verify) {
return error.AuthenticationFailed;
}
}
};
}
inline fn xorBlocks(x: Block, y: Block) Block {
var z: Block = x;
for (z) |*v, i| {
v.* = x[i] ^ y[i];
}
return z;
}
inline fn xorWith(x: *Block, y: Block) void {
for (x) |*v, i| {
v.* ^= y[i];
}
}
const hexToBytes = std.fmt.hexToBytes;
test "AesOcb test vector 1" {
var k: [Aes128Ocb.key_length]u8 = undefined;
var nonce: [Aes128Ocb.nonce_length]u8 = undefined;
var tag: [Aes128Ocb.tag_length]u8 = undefined;
_ = try hexToBytes(&k, "000102030405060708090A0B0C0D0E0F");
_ = try hexToBytes(&nonce, "BBAA99887766554433221100");
var c: [0]u8 = undefined;
Aes128Ocb.encrypt(&c, &tag, "", "", nonce, k);
var expected_tag: [tag.len]u8 = undefined;
_ = try hexToBytes(&expected_tag, "785407BFFFC8AD9EDCC5520AC9111EE6");
var m: [0]u8 = undefined;
try Aes128Ocb.decrypt(&m, "", tag, "", nonce, k);
}
test "AesOcb test vector 2" {
var k: [Aes128Ocb.key_length]u8 = undefined;
var nonce: [Aes128Ocb.nonce_length]u8 = undefined;
var tag: [Aes128Ocb.tag_length]u8 = undefined;
var ad: [40]u8 = undefined;
_ = try hexToBytes(&k, "000102030405060708090A0B0C0D0E0F");
_ = try hexToBytes(&ad, "000102030405060708090A0B0C0D0E0F101112131415161718191A1B1C1D1E1F2021222324252627");
_ = try hexToBytes(&nonce, "BBAA9988776655443322110E");
var c: [0]u8 = undefined;
Aes128Ocb.encrypt(&c, &tag, "", &ad, nonce, k);
var expected_tag: [tag.len]u8 = undefined;
_ = try hexToBytes(&expected_tag, "C5CD9D1850C141E358649994EE701B68");
var m: [0]u8 = undefined;
try Aes128Ocb.decrypt(&m, &c, tag, &ad, nonce, k);
}
test "AesOcb test vector 3" {
var k: [Aes128Ocb.key_length]u8 = undefined;
var nonce: [Aes128Ocb.nonce_length]u8 = undefined;
var tag: [Aes128Ocb.tag_length]u8 = undefined;
var m: [40]u8 = undefined;
var c: [m.len]u8 = undefined;
_ = try hexToBytes(&k, "000102030405060708090A0B0C0D0E0F");
_ = try hexToBytes(&m, "000102030405060708090A0B0C0D0E0F101112131415161718191A1B1C1D1E1F2021222324252627");
_ = try hexToBytes(&nonce, "BBAA9988776655443322110F");
Aes128Ocb.encrypt(&c, &tag, &m, "", nonce, k);
var expected_c: [c.len]u8 = undefined;
var expected_tag: [tag.len]u8 = undefined;
_ = try hexToBytes(&expected_tag, "479AD363AC366B95A98CA5F3000B1479");
_ = try hexToBytes(&expected_c, "4412923493C57D5DE0D700F753CCE0D1D2D95060122E9F15A5DDBFC5787E50B5CC55EE507BCB084E");
var m2: [m.len]u8 = undefined;
try Aes128Ocb.decrypt(&m2, &c, tag, "", nonce, k);
assert(mem.eql(u8, &m, &m2));
}
test "AesOcb test vector 4" {
var k: [Aes128Ocb.key_length]u8 = undefined;
var nonce: [Aes128Ocb.nonce_length]u8 = undefined;
var tag: [Aes128Ocb.tag_length]u8 = undefined;
var m: [40]u8 = undefined;
var ad = m;
var c: [m.len]u8 = undefined;
_ = try hexToBytes(&k, "000102030405060708090A0B0C0D0E0F");
_ = try hexToBytes(&m, "000102030405060708090A0B0C0D0E0F101112131415161718191A1B1C1D1E1F2021222324252627");
_ = try hexToBytes(&nonce, "BBAA99887766554433221104");
Aes128Ocb.encrypt(&c, &tag, &m, &ad, nonce, k);
var expected_c: [c.len]u8 = undefined;
var expected_tag: [tag.len]u8 = undefined;
_ = try hexToBytes(&expected_tag, "3AD7A4FF3835B8C5701C1CCEC8FC3358");
_ = try hexToBytes(&expected_c, "571D535B60B277188BE5147170A9A22C");
var m2: [m.len]u8 = undefined;
try Aes128Ocb.decrypt(&m2, &c, tag, &ad, nonce, k);
assert(mem.eql(u8, &m, &m2));
}
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