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SHA-256: the rotations masked again, as the integer rule asks

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The unmasked rotations of the previous commit were exact, but on the VM
they left values of up to 62 bits in the sums, against the rule of the
package: every value in 32 bits on the VM as on the web. Masked again, the
unrolled rounds are as fast: PBKDF2 at 600 000 iterations takes about 1 s
on the VM.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
v0.11
dev 2 days ago
parent a2e2bbfcd6
commit 4850b6bca8
1 changed files with 60 additions and 39 deletions
Show Stats Download Patch File Download Diff File

99
lib/src/sha256.dart
Unescape View File

@ -52,17 +52,22 @@ const _iv = [
/// Compresses the 16 words of [w] (big-endian words of one block, w[0..15];
/// w[16..63] are scratch) into the eight words of [state].
///
/// The left halves of the rotations are not masked: on the VM their bits
/// above 32 only reach sums that are masked before any other use, and an
/// addition carries upward only; on the web, `<<` keeps 32 bits itself. The
/// rounds are unrolled by eight, so that the working variables rotate by
/// name instead of by assignment.
/// Every value stays in 32 bits on the VM as on the web: the left half of
/// each rotation is masked, and each sum of at most five words is masked
/// before any other use. The rounds are unrolled by eight, so that the
/// working variables rotate by name instead of by assignment.
void _compress(Uint32List state, Uint32List w) {
for (var t = 16; t < 64; t++) {
final x = w[t - 15];
final y = w[t - 2];
final s0 = (x >>> 7 | x << 25) ^ (x >>> 18 | x << 14) ^ x >>> 3;
final s1 = (y >>> 17 | y << 15) ^ (y >>> 19 | y << 13) ^ y >>> 10;
final s0 =
(x >>> 7 | x << 25 & _mask32) ^
(x >>> 18 | x << 14 & _mask32) ^
x >>> 3;
final s1 =
(y >>> 17 | y << 15 & _mask32) ^
(y >>> 19 | y << 13 & _mask32) ^
y >>> 10;
w[t] = (w[t - 16] + s0 + w[t - 7] + s1) & _mask32;
}
var a = state[0];
@ -77,7 +82,9 @@ void _compress(Uint32List state, Uint32List w) {
// Round t + 0.
final t0 =
(h +
((e >>> 6 | e << 26) ^ (e >>> 11 | e << 21) ^ (e >>> 25 | e << 7)) +
((e >>> 6 | e << 26 & _mask32) ^
(e >>> 11 | e << 21 & _mask32) ^
(e >>> 25 | e << 7 & _mask32)) +
((e & f) ^ ((e ^ _mask32) & g)) +
_k[t + 0] +
w[t + 0]) &
@ -85,15 +92,17 @@ void _compress(Uint32List state, Uint32List w) {
d = (d + t0) & _mask32;
h =
(t0 +
((a >>> 2 | a << 30) ^
(a >>> 13 | a << 19) ^
(a >>> 22 | a << 10)) +
((a >>> 2 | a << 30 & _mask32) ^
(a >>> 13 | a << 19 & _mask32) ^
(a >>> 22 | a << 10 & _mask32)) +
((a & b) ^ (a & c) ^ (b & c))) &
_mask32;
// Round t + 1.
final t1 =
(g +
((d >>> 6 | d << 26) ^ (d >>> 11 | d << 21) ^ (d >>> 25 | d << 7)) +
((d >>> 6 | d << 26 & _mask32) ^
(d >>> 11 | d << 21 & _mask32) ^
(d >>> 25 | d << 7 & _mask32)) +
((d & e) ^ ((d ^ _mask32) & f)) +
_k[t + 1] +
w[t + 1]) &
@ -101,15 +110,17 @@ void _compress(Uint32List state, Uint32List w) {
c = (c + t1) & _mask32;
g =
(t1 +
((h >>> 2 | h << 30) ^
(h >>> 13 | h << 19) ^
(h >>> 22 | h << 10)) +
((h >>> 2 | h << 30 & _mask32) ^
(h >>> 13 | h << 19 & _mask32) ^
(h >>> 22 | h << 10 & _mask32)) +
((h & a) ^ (h & b) ^ (a & b))) &
_mask32;
// Round t + 2.
final t2 =
(f +
((c >>> 6 | c << 26) ^ (c >>> 11 | c << 21) ^ (c >>> 25 | c << 7)) +
((c >>> 6 | c << 26 & _mask32) ^
(c >>> 11 | c << 21 & _mask32) ^
(c >>> 25 | c << 7 & _mask32)) +
((c & d) ^ ((c ^ _mask32) & e)) +
_k[t + 2] +
w[t + 2]) &
@ -117,15 +128,17 @@ void _compress(Uint32List state, Uint32List w) {
b = (b + t2) & _mask32;
f =
(t2 +
((g >>> 2 | g << 30) ^
(g >>> 13 | g << 19) ^
(g >>> 22 | g << 10)) +
((g >>> 2 | g << 30 & _mask32) ^
(g >>> 13 | g << 19 & _mask32) ^
(g >>> 22 | g << 10 & _mask32)) +
((g & h) ^ (g & a) ^ (h & a))) &
_mask32;
// Round t + 3.
final t3 =
(e +
((b >>> 6 | b << 26) ^ (b >>> 11 | b << 21) ^ (b >>> 25 | b << 7)) +
((b >>> 6 | b << 26 & _mask32) ^
(b >>> 11 | b << 21 & _mask32) ^
(b >>> 25 | b << 7 & _mask32)) +
((b & c) ^ ((b ^ _mask32) & d)) +
_k[t + 3] +
w[t + 3]) &
@ -133,15 +146,17 @@ void _compress(Uint32List state, Uint32List w) {
a = (a + t3) & _mask32;
e =
(t3 +
((f >>> 2 | f << 30) ^
(f >>> 13 | f << 19) ^
(f >>> 22 | f << 10)) +
((f >>> 2 | f << 30 & _mask32) ^
(f >>> 13 | f << 19 & _mask32) ^
(f >>> 22 | f << 10 & _mask32)) +
((f & g) ^ (f & h) ^ (g & h))) &
_mask32;
// Round t + 4.
final t4 =
(d +
((a >>> 6 | a << 26) ^ (a >>> 11 | a << 21) ^ (a >>> 25 | a << 7)) +
((a >>> 6 | a << 26 & _mask32) ^
(a >>> 11 | a << 21 & _mask32) ^
(a >>> 25 | a << 7 & _mask32)) +
((a & b) ^ ((a ^ _mask32) & c)) +
_k[t + 4] +
w[t + 4]) &
@ -149,15 +164,17 @@ void _compress(Uint32List state, Uint32List w) {
h = (h + t4) & _mask32;
d =
(t4 +
((e >>> 2 | e << 30) ^
(e >>> 13 | e << 19) ^
(e >>> 22 | e << 10)) +
((e >>> 2 | e << 30 & _mask32) ^
(e >>> 13 | e << 19 & _mask32) ^
(e >>> 22 | e << 10 & _mask32)) +
((e & f) ^ (e & g) ^ (f & g))) &
_mask32;
// Round t + 5.
final t5 =
(c +
((h >>> 6 | h << 26) ^ (h >>> 11 | h << 21) ^ (h >>> 25 | h << 7)) +
((h >>> 6 | h << 26 & _mask32) ^
(h >>> 11 | h << 21 & _mask32) ^
(h >>> 25 | h << 7 & _mask32)) +
((h & a) ^ ((h ^ _mask32) & b)) +
_k[t + 5] +
w[t + 5]) &
@ -165,15 +182,17 @@ void _compress(Uint32List state, Uint32List w) {
g = (g + t5) & _mask32;
c =
(t5 +
((d >>> 2 | d << 30) ^
(d >>> 13 | d << 19) ^
(d >>> 22 | d << 10)) +
((d >>> 2 | d << 30 & _mask32) ^
(d >>> 13 | d << 19 & _mask32) ^
(d >>> 22 | d << 10 & _mask32)) +
((d & e) ^ (d & f) ^ (e & f))) &
_mask32;
// Round t + 6.
final t6 =
(b +
((g >>> 6 | g << 26) ^ (g >>> 11 | g << 21) ^ (g >>> 25 | g << 7)) +
((g >>> 6 | g << 26 & _mask32) ^
(g >>> 11 | g << 21 & _mask32) ^
(g >>> 25 | g << 7 & _mask32)) +
((g & h) ^ ((g ^ _mask32) & a)) +
_k[t + 6] +
w[t + 6]) &
@ -181,15 +200,17 @@ void _compress(Uint32List state, Uint32List w) {
f = (f + t6) & _mask32;
b =
(t6 +
((c >>> 2 | c << 30) ^
(c >>> 13 | c << 19) ^
(c >>> 22 | c << 10)) +
((c >>> 2 | c << 30 & _mask32) ^
(c >>> 13 | c << 19 & _mask32) ^
(c >>> 22 | c << 10 & _mask32)) +
((c & d) ^ (c & e) ^ (d & e))) &
_mask32;
// Round t + 7.
final t7 =
(a +
((f >>> 6 | f << 26) ^ (f >>> 11 | f << 21) ^ (f >>> 25 | f << 7)) +
((f >>> 6 | f << 26 & _mask32) ^
(f >>> 11 | f << 21 & _mask32) ^
(f >>> 25 | f << 7 & _mask32)) +
((f & g) ^ ((f ^ _mask32) & h)) +
_k[t + 7] +
w[t + 7]) &
@ -197,9 +218,9 @@ void _compress(Uint32List state, Uint32List w) {
e = (e + t7) & _mask32;
a =
(t7 +
((b >>> 2 | b << 30) ^
(b >>> 13 | b << 19) ^
(b >>> 22 | b << 10)) +
((b >>> 2 | b << 30 & _mask32) ^
(b >>> 13 | b << 19 & _mask32) ^
(b >>> 22 | b << 10 & _mask32)) +
((b & c) ^ (b & d) ^ (c & d))) &
_mask32;
}

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