/home/kueuepay/public_html/vendor/paragonie/sodium_compat/src/Core/Ristretto255.php
<?php
/**
* Class ParagonIE_Sodium_Core_Ristretto255
*/
class ParagonIE_Sodium_Core_Ristretto255 extends ParagonIE_Sodium_Core_Ed25519
{
const crypto_core_ristretto255_HASHBYTES = 64;
const HASH_SC_L = 48;
const CORE_H2C_SHA256 = 1;
const CORE_H2C_SHA512 = 2;
/**
* @param ParagonIE_Sodium_Core_Curve25519_Fe $f
* @param int $b
* @return ParagonIE_Sodium_Core_Curve25519_Fe
*/
public static function fe_cneg(ParagonIE_Sodium_Core_Curve25519_Fe $f, $b)
{
$negf = self::fe_neg($f);
return self::fe_cmov($f, $negf, $b);
}
/**
* @param ParagonIE_Sodium_Core_Curve25519_Fe $f
* @return ParagonIE_Sodium_Core_Curve25519_Fe
* @throws SodiumException
*/
public static function fe_abs(ParagonIE_Sodium_Core_Curve25519_Fe $f)
{
return self::fe_cneg($f, self::fe_isnegative($f));
}
/**
* Returns 0 if this field element results in all NUL bytes.
*
* @internal You should not use this directly from another application
*
* @param ParagonIE_Sodium_Core_Curve25519_Fe $f
* @return int
* @throws SodiumException
*/
public static function fe_iszero(ParagonIE_Sodium_Core_Curve25519_Fe $f)
{
static $zero;
if ($zero === null) {
$zero = str_repeat("\x00", 32);
}
/** @var string $zero */
$str = self::fe_tobytes($f);
$d = 0;
for ($i = 0; $i < 32; ++$i) {
$d |= self::chrToInt($str[$i]);
}
return (($d - 1) >> 31) & 1;
}
/**
* @param ParagonIE_Sodium_Core_Curve25519_Fe $u
* @param ParagonIE_Sodium_Core_Curve25519_Fe $v
* @return array{x: ParagonIE_Sodium_Core_Curve25519_Fe, nonsquare: int}
*
* @throws SodiumException
*/
public static function ristretto255_sqrt_ratio_m1(
ParagonIE_Sodium_Core_Curve25519_Fe $u,
ParagonIE_Sodium_Core_Curve25519_Fe $v
) {
$sqrtm1 = ParagonIE_Sodium_Core_Curve25519_Fe::fromArray(self::$sqrtm1);
$v3 = self::fe_mul(
self::fe_sq($v),
$v
); /* v3 = v^3 */
$x = self::fe_mul(
self::fe_mul(
self::fe_sq($v3),
$u
),
$v
); /* x = uv^7 */
$x = self::fe_mul(
self::fe_mul(
self::fe_pow22523($x), /* x = (uv^7)^((q-5)/8) */
$v3
),
$u
); /* x = uv^3(uv^7)^((q-5)/8) */
$vxx = self::fe_mul(
self::fe_sq($x),
$v
); /* vx^2 */
$m_root_check = self::fe_sub($vxx, $u); /* vx^2-u */
$p_root_check = self::fe_add($vxx, $u); /* vx^2+u */
$f_root_check = self::fe_mul($u, $sqrtm1); /* u*sqrt(-1) */
$f_root_check = self::fe_add($vxx, $f_root_check); /* vx^2+u*sqrt(-1) */
$has_m_root = self::fe_iszero($m_root_check);
$has_p_root = self::fe_iszero($p_root_check);
$has_f_root = self::fe_iszero($f_root_check);
$x_sqrtm1 = self::fe_mul($x, $sqrtm1); /* x*sqrt(-1) */
$x = self::fe_abs(
self::fe_cmov($x, $x_sqrtm1, $has_p_root | $has_f_root)
);
return array(
'x' => $x,
'nonsquare' => $has_m_root | $has_p_root
);
}
/**
* @param string $s
* @return int
* @throws SodiumException
*/
public static function ristretto255_point_is_canonical($s)
{
$c = (self::chrToInt($s[31]) & 0x7f) ^ 0x7f;
for ($i = 30; $i > 0; --$i) {
$c |= self::chrToInt($s[$i]) ^ 0xff;
}
$c = ($c - 1) >> 8;
$d = (0xed - 1 - self::chrToInt($s[0])) >> 8;
$e = self::chrToInt($s[31]) >> 7;
return 1 - ((($c & $d) | $e | self::chrToInt($s[0])) & 1);
}
/**
* @param string $s
* @param bool $skipCanonicalCheck
* @return array{h: ParagonIE_Sodium_Core_Curve25519_Ge_P3, res: int}
* @throws SodiumException
*/
public static function ristretto255_frombytes($s, $skipCanonicalCheck = false)
{
if (!$skipCanonicalCheck) {
if (!self::ristretto255_point_is_canonical($s)) {
throw new SodiumException('S is not canonical');
}
}
$s_ = self::fe_frombytes($s);
$ss = self::fe_sq($s_); /* ss = s^2 */
$u1 = self::fe_sub(self::fe_1(), $ss); /* u1 = 1-ss */
$u1u1 = self::fe_sq($u1); /* u1u1 = u1^2 */
$u2 = self::fe_add(self::fe_1(), $ss); /* u2 = 1+ss */
$u2u2 = self::fe_sq($u2); /* u2u2 = u2^2 */
$v = self::fe_mul(
ParagonIE_Sodium_Core_Curve25519_Fe::fromArray(self::$d),
$u1u1
); /* v = d*u1^2 */
$v = self::fe_neg($v); /* v = -d*u1^2 */
$v = self::fe_sub($v, $u2u2); /* v = -(d*u1^2)-u2^2 */
$v_u2u2 = self::fe_mul($v, $u2u2); /* v_u2u2 = v*u2^2 */
// fe25519_1(one);
// notsquare = ristretto255_sqrt_ratio_m1(inv_sqrt, one, v_u2u2);
$one = self::fe_1();
$result = self::ristretto255_sqrt_ratio_m1($one, $v_u2u2);
$inv_sqrt = $result['x'];
$notsquare = $result['nonsquare'];
$h = new ParagonIE_Sodium_Core_Curve25519_Ge_P3();
$h->X = self::fe_mul($inv_sqrt, $u2);
$h->Y = self::fe_mul(self::fe_mul($inv_sqrt, $h->X), $v);
$h->X = self::fe_mul($h->X, $s_);
$h->X = self::fe_abs(
self::fe_add($h->X, $h->X)
);
$h->Y = self::fe_mul($u1, $h->Y);
$h->Z = self::fe_1();
$h->T = self::fe_mul($h->X, $h->Y);
$res = - ((1 - $notsquare) | self::fe_isnegative($h->T) | self::fe_iszero($h->Y));
return array('h' => $h, 'res' => $res);
}
/**
* @param ParagonIE_Sodium_Core_Curve25519_Ge_P3 $h
* @return string
* @throws SodiumException
*/
public static function ristretto255_p3_tobytes(ParagonIE_Sodium_Core_Curve25519_Ge_P3 $h)
{
$sqrtm1 = ParagonIE_Sodium_Core_Curve25519_Fe::fromArray(self::$sqrtm1);
$invsqrtamd = ParagonIE_Sodium_Core_Curve25519_Fe::fromArray(self::$invsqrtamd);
$u1 = self::fe_add($h->Z, $h->Y); /* u1 = Z+Y */
$zmy = self::fe_sub($h->Z, $h->Y); /* zmy = Z-Y */
$u1 = self::fe_mul($u1, $zmy); /* u1 = (Z+Y)*(Z-Y) */
$u2 = self::fe_mul($h->X, $h->Y); /* u2 = X*Y */
$u1_u2u2 = self::fe_mul(self::fe_sq($u2), $u1); /* u1_u2u2 = u1*u2^2 */
$one = self::fe_1();
// fe25519_1(one);
// (void) ristretto255_sqrt_ratio_m1(inv_sqrt, one, u1_u2u2);
$result = self::ristretto255_sqrt_ratio_m1($one, $u1_u2u2);
$inv_sqrt = $result['x'];
$den1 = self::fe_mul($inv_sqrt, $u1); /* den1 = inv_sqrt*u1 */
$den2 = self::fe_mul($inv_sqrt, $u2); /* den2 = inv_sqrt*u2 */
$z_inv = self::fe_mul($h->T, self::fe_mul($den1, $den2)); /* z_inv = den1*den2*T */
$ix = self::fe_mul($h->X, $sqrtm1); /* ix = X*sqrt(-1) */
$iy = self::fe_mul($h->Y, $sqrtm1); /* iy = Y*sqrt(-1) */
$eden = self::fe_mul($den1, $invsqrtamd);
$t_z_inv = self::fe_mul($h->T, $z_inv); /* t_z_inv = T*z_inv */
$rotate = self::fe_isnegative($t_z_inv);
$x_ = self::fe_copy($h->X);
$y_ = self::fe_copy($h->Y);
$den_inv = self::fe_copy($den2);
$x_ = self::fe_cmov($x_, $iy, $rotate);
$y_ = self::fe_cmov($y_, $ix, $rotate);
$den_inv = self::fe_cmov($den_inv, $eden, $rotate);
$x_z_inv = self::fe_mul($x_, $z_inv);
$y_ = self::fe_cneg($y_, self::fe_isnegative($x_z_inv));
// fe25519_sub(s_, h->Z, y_);
// fe25519_mul(s_, den_inv, s_);
// fe25519_abs(s_, s_);
// fe25519_tobytes(s, s_);
return self::fe_tobytes(
self::fe_abs(
self::fe_mul(
$den_inv,
self::fe_sub($h->Z, $y_)
)
)
);
}
/**
* @param ParagonIE_Sodium_Core_Curve25519_Fe $t
* @return ParagonIE_Sodium_Core_Curve25519_Ge_P3
*
* @throws SodiumException
*/
public static function ristretto255_elligator(ParagonIE_Sodium_Core_Curve25519_Fe $t)
{
$sqrtm1 = ParagonIE_Sodium_Core_Curve25519_Fe::fromArray(self::$sqrtm1);
$onemsqd = ParagonIE_Sodium_Core_Curve25519_Fe::fromArray(self::$onemsqd);
$d = ParagonIE_Sodium_Core_Curve25519_Fe::fromArray(self::$d);
$sqdmone = ParagonIE_Sodium_Core_Curve25519_Fe::fromArray(self::$sqdmone);
$sqrtadm1 = ParagonIE_Sodium_Core_Curve25519_Fe::fromArray(self::$sqrtadm1);
$one = self::fe_1();
$r = self::fe_mul($sqrtm1, self::fe_sq($t)); /* r = sqrt(-1)*t^2 */
$u = self::fe_mul(self::fe_add($r, $one), $onemsqd); /* u = (r+1)*(1-d^2) */
$c = self::fe_neg(self::fe_1()); /* c = -1 */
$rpd = self::fe_add($r, $d); /* rpd = r+d */
$v = self::fe_mul(
self::fe_sub(
$c,
self::fe_mul($r, $d)
),
$rpd
); /* v = (c-r*d)*(r+d) */
$result = self::ristretto255_sqrt_ratio_m1($u, $v);
$s = $result['x'];
$wasnt_square = 1 - $result['nonsquare'];
$s_prime = self::fe_neg(
self::fe_abs(
self::fe_mul($s, $t)
)
); /* s_prime = -|s*t| */
$s = self::fe_cmov($s, $s_prime, $wasnt_square);
$c = self::fe_cmov($c, $r, $wasnt_square);
// fe25519_sub(n, r, one); /* n = r-1 */
// fe25519_mul(n, n, c); /* n = c*(r-1) */
// fe25519_mul(n, n, ed25519_sqdmone); /* n = c*(r-1)*(d-1)^2 */
// fe25519_sub(n, n, v); /* n = c*(r-1)*(d-1)^2-v */
$n = self::fe_sub(
self::fe_mul(
self::fe_mul(
self::fe_sub($r, $one),
$c
),
$sqdmone
),
$v
); /* n = c*(r-1)*(d-1)^2-v */
$w0 = self::fe_mul(
self::fe_add($s, $s),
$v
); /* w0 = 2s*v */
$w1 = self::fe_mul($n, $sqrtadm1); /* w1 = n*sqrt(ad-1) */
$ss = self::fe_sq($s); /* ss = s^2 */
$w2 = self::fe_sub($one, $ss); /* w2 = 1-s^2 */
$w3 = self::fe_add($one, $ss); /* w3 = 1+s^2 */
return new ParagonIE_Sodium_Core_Curve25519_Ge_P3(
self::fe_mul($w0, $w3),
self::fe_mul($w2, $w1),
self::fe_mul($w1, $w3),
self::fe_mul($w0, $w2)
);
}
/**
* @param string $h
* @return string
* @throws SodiumException
*/
public static function ristretto255_from_hash($h)
{
if (self::strlen($h) !== 64) {
throw new SodiumException('Hash must be 64 bytes');
}
//fe25519_frombytes(r0, h);
//fe25519_frombytes(r1, h + 32);
$r0 = self::fe_frombytes(self::substr($h, 0, 32));
$r1 = self::fe_frombytes(self::substr($h, 32, 32));
//ristretto255_elligator(&p0, r0);
//ristretto255_elligator(&p1, r1);
$p0 = self::ristretto255_elligator($r0);
$p1 = self::ristretto255_elligator($r1);
//ge25519_p3_to_cached(&p1_cached, &p1);
//ge25519_add_cached(&p_p1p1, &p0, &p1_cached);
$p_p1p1 = self::ge_add(
$p0,
self::ge_p3_to_cached($p1)
);
//ge25519_p1p1_to_p3(&p, &p_p1p1);
//ristretto255_p3_tobytes(s, &p);
return self::ristretto255_p3_tobytes(
self::ge_p1p1_to_p3($p_p1p1)
);
}
/**
* @param string $p
* @return int
* @throws SodiumException
*/
public static function is_valid_point($p)
{
$result = self::ristretto255_frombytes($p);
if ($result['res'] !== 0) {
return 0;
}
return 1;
}
/**
* @param string $p
* @param string $q
* @return string
* @throws SodiumException
*/
public static function ristretto255_add($p, $q)
{
$p_res = self::ristretto255_frombytes($p);
$q_res = self::ristretto255_frombytes($q);
if ($p_res['res'] !== 0 || $q_res['res'] !== 0) {
throw new SodiumException('Could not add points');
}
$p_p3 = $p_res['h'];
$q_p3 = $q_res['h'];
$q_cached = self::ge_p3_to_cached($q_p3);
$r_p1p1 = self::ge_add($p_p3, $q_cached);
$r_p3 = self::ge_p1p1_to_p3($r_p1p1);
return self::ristretto255_p3_tobytes($r_p3);
}
/**
* @param string $p
* @param string $q
* @return string
* @throws SodiumException
*/
public static function ristretto255_sub($p, $q)
{
$p_res = self::ristretto255_frombytes($p);
$q_res = self::ristretto255_frombytes($q);
if ($p_res['res'] !== 0 || $q_res['res'] !== 0) {
throw new SodiumException('Could not add points');
}
$p_p3 = $p_res['h'];
$q_p3 = $q_res['h'];
$q_cached = self::ge_p3_to_cached($q_p3);
$r_p1p1 = self::ge_sub($p_p3, $q_cached);
$r_p3 = self::ge_p1p1_to_p3($r_p1p1);
return self::ristretto255_p3_tobytes($r_p3);
}
/**
* @param int $hLen
* @param ?string $ctx
* @param string $msg
* @return string
* @throws SodiumException
* @psalm-suppress PossiblyInvalidArgument hash API
*/
protected static function h2c_string_to_hash_sha256($hLen, $ctx, $msg)
{
$h = array_fill(0, $hLen, 0);
$ctx_len = !is_null($ctx) ? self::strlen($ctx) : 0;
if ($hLen > 0xff) {
throw new SodiumException('Hash must be less than 256 bytes');
}
if ($ctx_len > 0xff) {
$st = hash_init('sha256');
self::hash_update($st, "H2C-OVERSIZE-DST-");
self::hash_update($st, $ctx);
$ctx = hash_final($st, true);
$ctx_len = 32;
}
$t = array(0, $hLen, 0);
$ux = str_repeat("\0", 64);
$st = hash_init('sha256');
self::hash_update($st, $ux);
self::hash_update($st, $msg);
self::hash_update($st, self::intArrayToString($t));
self::hash_update($st, $ctx);
self::hash_update($st, self::intToChr($ctx_len));
$u0 = hash_final($st, true);
for ($i = 0; $i < $hLen; $i += 64) {
$ux = self::xorStrings($ux, $u0);
++$t[2];
$st = hash_init('sha256');
self::hash_update($st, $ux);
self::hash_update($st, self::intToChr($t[2]));
self::hash_update($st, $ctx);
self::hash_update($st, self::intToChr($ctx_len));
$ux = hash_final($st, true);
$amount = min($hLen - $i, 64);
for ($j = 0; $j < $amount; ++$j) {
$h[$i + $j] = self::chrToInt($ux[$i]);
}
}
return self::intArrayToString(array_slice($h, 0, $hLen));
}
/**
* @param int $hLen
* @param ?string $ctx
* @param string $msg
* @return string
* @throws SodiumException
* @psalm-suppress PossiblyInvalidArgument hash API
*/
protected static function h2c_string_to_hash_sha512($hLen, $ctx, $msg)
{
$h = array_fill(0, $hLen, 0);
$ctx_len = !is_null($ctx) ? self::strlen($ctx) : 0;
if ($hLen > 0xff) {
throw new SodiumException('Hash must be less than 256 bytes');
}
if ($ctx_len > 0xff) {
$st = hash_init('sha256');
self::hash_update($st, "H2C-OVERSIZE-DST-");
self::hash_update($st, $ctx);
$ctx = hash_final($st, true);
$ctx_len = 32;
}
$t = array(0, $hLen, 0);
$ux = str_repeat("\0", 128);
$st = hash_init('sha512');
self::hash_update($st, $ux);
self::hash_update($st, $msg);
self::hash_update($st, self::intArrayToString($t));
self::hash_update($st, $ctx);
self::hash_update($st, self::intToChr($ctx_len));
$u0 = hash_final($st, true);
for ($i = 0; $i < $hLen; $i += 128) {
$ux = self::xorStrings($ux, $u0);
++$t[2];
$st = hash_init('sha512');
self::hash_update($st, $ux);
self::hash_update($st, self::intToChr($t[2]));
self::hash_update($st, $ctx);
self::hash_update($st, self::intToChr($ctx_len));
$ux = hash_final($st, true);
$amount = min($hLen - $i, 128);
for ($j = 0; $j < $amount; ++$j) {
$h[$i + $j] = self::chrToInt($ux[$i]);
}
}
return self::intArrayToString(array_slice($h, 0, $hLen));
}
/**
* @param int $hLen
* @param ?string $ctx
* @param string $msg
* @param int $hash_alg
* @return string
* @throws SodiumException
*/
public static function h2c_string_to_hash($hLen, $ctx, $msg, $hash_alg)
{
switch ($hash_alg) {
case self::CORE_H2C_SHA256:
return self::h2c_string_to_hash_sha256($hLen, $ctx, $msg);
case self::CORE_H2C_SHA512:
return self::h2c_string_to_hash_sha512($hLen, $ctx, $msg);
default:
throw new SodiumException('Invalid H2C hash algorithm');
}
}
/**
* @param ?string $ctx
* @param string $msg
* @param int $hash_alg
* @return string
* @throws SodiumException
*/
protected static function _string_to_element($ctx, $msg, $hash_alg)
{
return self::ristretto255_from_hash(
self::h2c_string_to_hash(self::crypto_core_ristretto255_HASHBYTES, $ctx, $msg, $hash_alg)
);
}
/**
* @return string
* @throws SodiumException
* @throws Exception
*/
public static function ristretto255_random()
{
return self::ristretto255_from_hash(
ParagonIE_Sodium_Compat::randombytes_buf(self::crypto_core_ristretto255_HASHBYTES)
);
}
/**
* @return string
* @throws SodiumException
*/
public static function ristretto255_scalar_random()
{
return self::scalar_random();
}
/**
* @param string $s
* @return string
* @throws SodiumException
*/
public static function ristretto255_scalar_complement($s)
{
return self::scalar_complement($s);
}
/**
* @param string $s
* @return string
*/
public static function ristretto255_scalar_invert($s)
{
return self::sc25519_invert($s);
}
/**
* @param string $s
* @return string
* @throws SodiumException
*/
public static function ristretto255_scalar_negate($s)
{
return self::scalar_negate($s);
}
/**
* @param string $x
* @param string $y
* @return string
*/
public static function ristretto255_scalar_add($x, $y)
{
return self::scalar_add($x, $y);
}
/**
* @param string $x
* @param string $y
* @return string
*/
public static function ristretto255_scalar_sub($x, $y)
{
return self::scalar_sub($x, $y);
}
/**
* @param string $x
* @param string $y
* @return string
*/
public static function ristretto255_scalar_mul($x, $y)
{
return self::sc25519_mul($x, $y);
}
/**
* @param string $ctx
* @param string $msg
* @param int $hash_alg
* @return string
* @throws SodiumException
*/
public static function ristretto255_scalar_from_string($ctx, $msg, $hash_alg)
{
$h = array_fill(0, 64, 0);
$h_be = self::stringToIntArray(
self::h2c_string_to_hash(
self::HASH_SC_L, $ctx, $msg, $hash_alg
)
);
for ($i = 0; $i < self::HASH_SC_L; ++$i) {
$h[$i] = $h_be[self::HASH_SC_L - 1 - $i];
}
return self::ristretto255_scalar_reduce(self::intArrayToString($h));
}
/**
* @param string $s
* @return string
*/
public static function ristretto255_scalar_reduce($s)
{
return self::sc_reduce($s);
}
/**
* @param string $n
* @param string $p
* @return string
* @throws SodiumException
*/
public static function scalarmult_ristretto255($n, $p)
{
if (self::strlen($n) !== 32) {
throw new SodiumException('Scalar must be 32 bytes, ' . self::strlen($p) . ' given.');
}
if (self::strlen($p) !== 32) {
throw new SodiumException('Point must be 32 bytes, ' . self::strlen($p) . ' given.');
}
$result = self::ristretto255_frombytes($p);
if ($result['res'] !== 0) {
throw new SodiumException('Could not multiply points');
}
$P = $result['h'];
$t = self::stringToIntArray($n);
$t[31] &= 0x7f;
$Q = self::ge_scalarmult(self::intArrayToString($t), $P);
$q = self::ristretto255_p3_tobytes($Q);
if (ParagonIE_Sodium_Compat::is_zero($q)) {
throw new SodiumException('An unknown error has occurred');
}
return $q;
}
/**
* @param string $n
* @return string
* @throws SodiumException
*/
public static function scalarmult_ristretto255_base($n)
{
$t = self::stringToIntArray($n);
$t[31] &= 0x7f;
$Q = self::ge_scalarmult_base(self::intArrayToString($t));
$q = self::ristretto255_p3_tobytes($Q);
if (ParagonIE_Sodium_Compat::is_zero($q)) {
throw new SodiumException('An unknown error has occurred');
}
return $q;
}
}
About
top
About NFC Pay: Our Story and Mission
NFC Pay was founded with a vision to transform the way people handle transactions. Our journey is defined by a commitment to innovation, security, and convenience. We strive to deliver seamless, user-friendly payment solutions that make everyday transactions effortless and secure. Our mission is to empower you to pay with ease and confidence, anytime, anywhere.
Simplifying Payments, One Tap at a Time.
Reinventing Your Wallet for Modern Convenience.
Smart Payments for a Effortless Lifestyle.
Experience the Ease of Tap and Pay.
Innovative Solutions for Your Daily Transactions.
Frequently Asked Questions About NFC Pay
Here are answers to some common questions about NFC Pay. We aim to provide clear and concise information to help you understand how our platform works and how it can benefit you. If you have any further inquiries, please don’t hesitate to contact our support team.
How do I register for NFC Pay?
Download the app and sign up using your email or phone number, then complete the verification process.
Is my payment information secure?
Yes, we use advanced encryption and security protocols to protect your payment details.
Can I add multiple cards to my NFC Pay wallet?
Absolutely, you can link multiple debit or credit cards to your wallet.
How do I transfer money to another user?
Go to the transfer section, select the recipient, enter the amount, and authorize the transfer.
What should I do if I forget my PIN?
Use the “Forgot PIN” feature in the app to reset it following the provided instructions.
How can I activate my merchant account?
Sign up for a merchant account through the app and follow the setup instructions to start accepting payments.
Can I track my payment status?
Yes, you can view and track your payment status in the account dashboard
In the digital age, privacy concerns have become increasingly paramount, prompting the European Union to enact the General Data Protection Regulation (GDPR) in 2018. Among its many provisions, GDPR sets strict guidelines for the collection and processing of personal data, including the use of cookies on websites. Privacy Policy
Allow
Decline
