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security: Add proper memory zeroizing for sensitive data

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- Zeroize clamped scalar 'e' in x25519_sw() before return
- Zeroize output on failure in compute_shared_secret()
- Zeroize output on failure in derive_public_key()
- Fix return value propagation in compute_shared_secret() and derive_public_key()
- Use memzero_explicit() consistently (not se050_x25519_sw_zeroize wrapper)
This commit is contained in:
km
2026-03-28 07:46:51 +09:00
parent a8d28882c7
commit d2081b3a9e
1 changed files with 20 additions and 7 deletions
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src/se050_x25519_sw.c
+20 -7
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@@ -584,7 +584,13 @@ int x25519_sw(uint8_t out[32], const uint8_t scalar[32], const uint8_t point[32]
/* Step 7: reject all-zero output */ /* Step 7: reject all-zero output */
uint8_t acc = 0; uint8_t acc = 0;
for (i = 0; i < 32; i++) acc |= out[i]; for (i = 0; i < 32; i++) acc |= out[i];
if (acc == 0) return -1; if (acc == 0) {
memzero_explicit(e, 32);
return -1;
}
/* Zeroize clamped scalar before return */
memzero_explicit(e, 32);
return 0; return 0;
} }
@@ -620,9 +626,13 @@ int se050_x25519_sw_compute_shared_secret(uint8_t *shared_secret,
uint8_t clamped[32]; uint8_t clamped[32];
memcpy(clamped, private_key, 32); memcpy(clamped, private_key, 32);
se050_x25519_sw_clamp(clamped); se050_x25519_sw_clamp(clamped);
x25519_sw(shared_secret, clamped, peer_public); int ret = x25519_sw(shared_secret, clamped, peer_public);
se050_x25519_sw_zeroize(clamped, 32); memzero_explicit(clamped, 32);
return 0; if (ret < 0) {
/* Zeroize output on failure */
memzero_explicit(shared_secret, 32);
}
return ret;
} }
int se050_x25519_sw_derive_public_key(uint8_t *public_key, int se050_x25519_sw_derive_public_key(uint8_t *public_key,
@@ -632,9 +642,12 @@ int se050_x25519_sw_derive_public_key(uint8_t *public_key,
uint8_t clamped[32]; uint8_t clamped[32];
memcpy(clamped, private_key, 32); memcpy(clamped, private_key, 32);
se050_x25519_sw_clamp(clamped); se050_x25519_sw_clamp(clamped);
x25519_sw(public_key, clamped, (const uint8_t*)"basepoint"); int ret = x25519_sw(public_key, clamped, (const uint8_t*)"basepoint");
se050_x25519_sw_zeroize(clamped, 32); memzero_explicit(clamped, 32);
return 0; if (ret < 0) {
memzero_explicit(public_key, 32);
}
return ret;
} }
#ifdef X25519_SW_TEST #ifdef X25519_SW_TEST