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fido2 derive: X-Wing (mlkem768x25519) split-custody support [UNTESTED] #30

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fido2 derive: X-Wing (mlkem768x25519) split-custody support [UNTESTED] #30

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46 changes: 45 additions & 1 deletion fido2/ok_extension.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -207,9 +207,53 @@ int16_t bridge_to_onlykey(uint8_t * _appid, uint8_t * keyh, int handle_len, uint
return ret;
}
memcpy(additional_data+1, client_handle+43, 32); // 32 bytes of data to include in key derivation
opt2++;
opt2++;
memset(ecc_public_key, 0, sizeof(ecc_public_key));

// ---- X-Wing (mlkem768x25519) split custody -------------------
// UNTESTED — validate on hardware. Wire keytype 5 -> opt2==KEYTYPE_XWING(6).
// Returns 64 bytes, encrypted under the transit key when opt3:
// DERIVE_PUBLIC_KEY -> [ pk_X(32) | mlkem_seed(32) ]
// DERIVE_SHAREDSEC -> [ ss_X(32) | mlkem_seed(32) ]
// sk_X (X25519) never leaves the device; the browser expands
// mlkem_seed and does the ML-KEM half locally. See
// onlykey.github.io src/plugins/age/INTEGRATION.md.
if (opt2 == KEYTYPE_XWING) {
// sk_X + pk_X from the web-derivation key (same as CURVE25519 path)
okcrypto_derive_key(KEYTYPE_CURVE25519, additional_data, RESERVED_KEY_WEB_DERIVATION);
// mlkem_seed = SHA256( sk_X || tag ) : one-way, domain-separated (!= sk_X)
uint8_t xwing_seed[32];
const char xwtag[] = "onlykey/xwing/mlkem768-seed/v1";
SHA256_CTX xc; sha256_init(&xc);
sha256_update(&xc, ecc_private_key, 32);
sha256_update(&xc, (const uint8_t*)xwtag, sizeof(xwtag) - 1);
sha256_final(&xc, xwing_seed);
uint8_t *xout = temp + 32 + sizeof(UNLOCKED) + 1;
if (opt1 == DERIVE_SHAREDSEC || opt1 == DERIVE_SHAREDSEC_REQ_PRESS) {
if (opt1 == DERIVE_SHAREDSEC_REQ_PRESS) {
int but;
device_set_status(CTAPHID_STATUS_UPNEEDED);
but = ctap_user_presence_test(CTAP2_UP_DELAY_MS);
if (but > 1) return CTAP2_ERR_PROCESSING;
else if (but < 0) return CTAP2_ERR_KEEPALIVE_CANCEL;
else if (but == 0) { pending_operation = 0; return CTAP2_ERR_ACTION_TIMEOUT; }
}
// ss_X = X25519(sk_X, ct_X); ct_X = input pubkey from the age stanza
uint8_t *ct_X = client_handle + 43 + 32;
if (okcrypto_shared_secret(ct_X, xout)) {
ret = CTAP2_ERR_OPERATION_DENIED;
printf2(TAG_ERR, "Error with X-Wing ss_X\n");
return ret;
}
} else {
memcpy(xout, ecc_public_key, 32); // pk_X
}
memcpy(xout + 32, xwing_seed, 32); // mlkem_seed
send_transport_response(temp, 32 + sizeof(UNLOCKED) + 1 + 64, opt3, false);
ret = send_stored_response(output);
return ret;
}

//Similar format to SSH derivation but use RESERVED_KEY_WEB_DERIVATION key
if (opt2 == KEYTYPE_NACL || opt2 == KEYTYPE_CURVE25519) {
okcrypto_derive_key(KEYTYPE_CURVE25519, additional_data, RESERVED_KEY_WEB_DERIVATION); //Curve25519
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