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ML-DSA constant-time hardening for caddq, poly_chknorm, decompose #2602

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Merged
merged 1 commit into from
Aug 12, 2025
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ML-DSA constant-time hardening for caddq, poly_chknorm, decompose #2602

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4 changes: 2 additions & 2 deletions crypto/fipsmodule/ml_dsa/ml_dsa_ref/poly.c
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Original file line number Diff line number Diff line change
Expand Up @@ -243,8 +243,8 @@ int ml_dsa_poly_chknorm(const ml_dsa_poly *a, int32_t B) {
data but we must not leak the sign of the centralized representative. */
for(i = 0; i < ML_DSA_N; ++i) {
/* Absolute value */
t = a->coeffs[i] >> 31;
t = a->coeffs[i] - (t & 2*a->coeffs[i]);
t = constant_time_select_int(constant_time_msb_w(a->coeffs[i]),
-a->coeffs[i], a->coeffs[i]);

if(t >= B) {
return 1;
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3 changes: 2 additions & 1 deletion crypto/fipsmodule/ml_dsa/ml_dsa_ref/reduce.c
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Expand Up @@ -52,7 +52,8 @@ int32_t ml_dsa_reduce32(int32_t a) {
* Returns r.
**************************************************/
int32_t ml_dsa_caddq(int32_t a) {
a += (a >> 31) & ML_DSA_Q;
// a = a < 0 ? a + Q : a;
a = constant_time_select_int(constant_time_msb_w(a), a + ML_DSA_Q, a);
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warning: call to undeclared function 'constant_time_msb_w'; ISO C99 and later do not support implicit function declarations [clang-diagnostic-implicit-function-declaration]

  a = constant_time_select_int(constant_time_msb_w(a), a + ML_DSA_Q, a);
                               ^

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warning: call to undeclared function 'constant_time_select_int'; ISO C99 and later do not support implicit function declarations [clang-diagnostic-implicit-function-declaration]

  a = constant_time_select_int(constant_time_msb_w(a), a + ML_DSA_Q, a);
      ^

return a;
}

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15 changes: 9 additions & 6 deletions crypto/fipsmodule/ml_dsa/ml_dsa_ref/rounding.c
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Expand Up @@ -44,17 +44,20 @@ int32_t ml_dsa_decompose(ml_dsa_params *params, int32_t *a0, int32_t a) {

int32_t a1;

a1 = (a + 127) >> 7;
a1 = (a + 127) >> 7;
if (params->gamma2 == (ML_DSA_Q-1)/32) {
a1 = (a1*1025 + (1 << 21)) >> 22;
a1 &= 15;
}
if (params->gamma2 == (ML_DSA_Q-1)/88) {
} else if (params->gamma2 == (ML_DSA_Q-1)/88) {
a1 = (a1*11275 + (1 << 23)) >> 24;
a1 ^= ((43 - a1) >> 31) & a1;
// a1 = 43 < a1 ? 0 : a1;
a1 = constant_time_select_int(constant_time_msb_w(43 - a1), 0, a1);
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warning: call to undeclared function 'constant_time_msb_w'; ISO C99 and later do not support implicit function declarations [clang-diagnostic-implicit-function-declaration]

    a1 = constant_time_select_int(constant_time_msb_w(43 - a1), 0, a1);
                                  ^

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warning: call to undeclared function 'constant_time_select_int'; ISO C99 and later do not support implicit function declarations [clang-diagnostic-implicit-function-declaration]

    a1 = constant_time_select_int(constant_time_msb_w(43 - a1), 0, a1);
         ^

}
*a0 = a - a1*2*params->gamma2;
*a0 -= (((ML_DSA_Q-1)/2 - *a0) >> 31) & ML_DSA_Q;

*a0 = a - a1*2*params->gamma2;
// a0 = (Q-1)/2 < a0 ? a0 - Q : a0;
*a0 = constant_time_select_int(constant_time_msb_w((ML_DSA_Q-1)/2 - *a0),
*a0 - ML_DSA_Q, *a0);
return a1;
}

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