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|
const std = @import("std");
const builtin = @import("builtin");
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(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(builtin.cpu.features, .aes);
const has_armaes = std.Target.aarch64.featureSetHas(builtin.cpu.features, .aes);
const wb: usize = if ((builtin.cpu.arch == .x86_64 and has_aesni) or (builtin.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(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(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(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(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));
}
|
