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contrib: keygen-html for generating keys in the browser 

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
This commit is contained in:
Jason A. Donenfeld 2017-12-01 13:31:33 +01:00
parent 30cf5eb883
commit bee819f289
4 changed files with 1020 additions and 0 deletions
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WireGuard Key Generation in JavaScript
======================================
Various people believe in JavaScript crypto, unfortunately. This small
example helps them fuel their poor taste.
It's possible to generate WireGuard keys (and thus configurations) in the
browser. The webpage here simulates talking to a server to exchange keys
and then generates a configuration file for the user to download.
Bugs
----
Who knows how emscripten actually compiles this and whether or not it
introduces interesting side-channel attacks.
Secrets aren't zerored after use. Maybe you can get around this with
some tricks taking advantage of browser allocator behavior and different
processes, but it seems pretty hard.

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<script src="curve25519_generate.js"></script>
<script>
// License: GPLv2
function generateWireguardKeypair()
{
var privateKey = Module._malloc(32);
var publicKey = Module._malloc(32);
Module._curve25519_generate_private(privateKey);
Module._curve25519_generate_public(publicKey, privateKey);
var privateBase64 = Module._malloc(45);
var publicBase64 = Module._malloc(45);
Module._key_to_base64(privateBase64, privateKey);
Module._key_to_base64(publicBase64, publicKey);
Module._free(privateKey);
Module._free(publicKey);
var keypair = {
publicKey: Module.Pointer_stringify(publicBase64),
privateKey: Module.Pointer_stringify(privateBase64)
};
Module._free(privateBase64);
Module._free(publicBase64);
return keypair;
}
function sendPubkeyToServer(pubkey, username, password)
{
alert("Sending " + username + ":" + password + " to server for new pubkey " + pubkey + "...");
// send info to server
var serverResponse = {
publicKey: "6spHEFoJrp9pijbxjJoS6fHjZaAWQqtdFFO/OtpVe3w=",
allowedIPs: [ "0.0.0.0/0", "::/0" ],
endpoint: "demo.wireguard.com:63321",
address: [ "192.168.18.42/32", "fd08:1234:1111::77/128" ],
dns: [ "8.8.8.8", "8.8.4.4" ]
}
return serverResponse;
}
function downloadNewConfiguration()
{
var keypair = generateWireguardKeypair();
var serverResponse = sendPubkeyToServer(keypair.publicKey, "zx2c4", "supersecretpassword");
var config = [];
config.push("[Interface]");
config.push("PrivateKey = " + keypair.privateKey);
config.push("Address = " + serverResponse.address.join(", "));
config.push("DNS = " + serverResponse.dns.join(", "));
config.push("");
config.push("[Peer]");
config.push("PublicKey = " + serverResponse.publicKey);
config.push("AllowedIPs = " + serverResponse.allowedIPs.join(", "));
config.push("Endpoint = " + serverResponse.endpoint);
config.push("");
config = config.join("\n");
var blob = new Blob([config], { type: "text/plain" });
var a = document.createElement("a");
a.download = "demo0.conf";
a.href = URL.createObjectURL(blob);
a.style.display = "none";
document.body.appendChild(a);
a.click();
document.body.removeChild(a);
}
</script>
<a href="javascript:downloadNewConfiguration()">Download a WireGuard configuration file</a>

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/* License: GPLv2 */
/* Build with emcc -O3 --memory-init-file 0 -o curve25519_generate.js curve25519_generate.c */
#include <emscripten.h>
typedef unsigned long long uint64_t;
typedef long long int64_t;
typedef int int32_t;
typedef unsigned int uint32_t;
typedef unsigned char uint8_t;
typedef int64_t limb;
/* Field element representation:
*
* Field elements are written as an array of signed, 64-bit limbs, least
* significant first. The value of the field element is:
* x[0] + 2^26·x[1] + x^51·x[2] + 2^102·x[3] + ...
*
* i.e. the limbs are 26, 25, 26, 25, ... bits wide.
*/
/* Sum two numbers: output += in */
static void fsum(limb *output, const limb *in)
{
unsigned int i;
for (i = 0; i < 10; i += 2) {
output[0 + i] = output[0 + i] + in[0 + i];
output[1 + i] = output[1 + i] + in[1 + i];
}
}
/* Find the difference of two numbers: output = in - output
* (note the order of the arguments!).
*/
static void fdifference(limb *output, const limb *in)
{
unsigned int i;
for (i = 0; i < 10; ++i) {
output[i] = in[i] - output[i];
}
}
/* Multiply a number by a scalar: output = in * scalar */
static void fscalar_product(limb *output, const limb *in, const limb scalar)
{
unsigned int i;
for (i = 0; i < 10; ++i) {
output[i] = in[i] * scalar;
}
}
/* Multiply two numbers: output = in2 * in
*
* output must be distinct to both inputs. The inputs are reduced coefficient
* form, the output is not.
*
* output[x] <= 14 * the largest product of the input limbs.
*/
static void fproduct(limb *output, const limb *in2, const limb *in)
{
output[0] = ((limb) ((int32_t) in2[0])) * ((int32_t) in[0]);
output[1] = ((limb) ((int32_t) in2[0])) * ((int32_t) in[1]) +
((limb) ((int32_t) in2[1])) * ((int32_t) in[0]);
output[2] = 2 * ((limb) ((int32_t) in2[1])) * ((int32_t) in[1]) +
((limb) ((int32_t) in2[0])) * ((int32_t) in[2]) +
((limb) ((int32_t) in2[2])) * ((int32_t) in[0]);
output[3] = ((limb) ((int32_t) in2[1])) * ((int32_t) in[2]) +
((limb) ((int32_t) in2[2])) * ((int32_t) in[1]) +
((limb) ((int32_t) in2[0])) * ((int32_t) in[3]) +
((limb) ((int32_t) in2[3])) * ((int32_t) in[0]);
output[4] = ((limb) ((int32_t) in2[2])) * ((int32_t) in[2]) +
2 * (((limb) ((int32_t) in2[1])) * ((int32_t) in[3]) +
((limb) ((int32_t) in2[3])) * ((int32_t) in[1])) +
((limb) ((int32_t) in2[0])) * ((int32_t) in[4]) +
((limb) ((int32_t) in2[4])) * ((int32_t) in[0]);
output[5] = ((limb) ((int32_t) in2[2])) * ((int32_t) in[3]) +
((limb) ((int32_t) in2[3])) * ((int32_t) in[2]) +
((limb) ((int32_t) in2[1])) * ((int32_t) in[4]) +
((limb) ((int32_t) in2[4])) * ((int32_t) in[1]) +
((limb) ((int32_t) in2[0])) * ((int32_t) in[5]) +
((limb) ((int32_t) in2[5])) * ((int32_t) in[0]);
output[6] = 2 * (((limb) ((int32_t) in2[3])) * ((int32_t) in[3]) +
((limb) ((int32_t) in2[1])) * ((int32_t) in[5]) +
((limb) ((int32_t) in2[5])) * ((int32_t) in[1])) +
((limb) ((int32_t) in2[2])) * ((int32_t) in[4]) +
((limb) ((int32_t) in2[4])) * ((int32_t) in[2]) +
((limb) ((int32_t) in2[0])) * ((int32_t) in[6]) +
((limb) ((int32_t) in2[6])) * ((int32_t) in[0]);
output[7] = ((limb) ((int32_t) in2[3])) * ((int32_t) in[4]) +
((limb) ((int32_t) in2[4])) * ((int32_t) in[3]) +
((limb) ((int32_t) in2[2])) * ((int32_t) in[5]) +
((limb) ((int32_t) in2[5])) * ((int32_t) in[2]) +
((limb) ((int32_t) in2[1])) * ((int32_t) in[6]) +
((limb) ((int32_t) in2[6])) * ((int32_t) in[1]) +
((limb) ((int32_t) in2[0])) * ((int32_t) in[7]) +
((limb) ((int32_t) in2[7])) * ((int32_t) in[0]);
output[8] = ((limb) ((int32_t) in2[4])) * ((int32_t) in[4]) +
2 * (((limb) ((int32_t) in2[3])) * ((int32_t) in[5]) +
((limb) ((int32_t) in2[5])) * ((int32_t) in[3]) +
((limb) ((int32_t) in2[1])) * ((int32_t) in[7]) +
((limb) ((int32_t) in2[7])) * ((int32_t) in[1])) +
((limb) ((int32_t) in2[2])) * ((int32_t) in[6]) +
((limb) ((int32_t) in2[6])) * ((int32_t) in[2]) +
((limb) ((int32_t) in2[0])) * ((int32_t) in[8]) +
((limb) ((int32_t) in2[8])) * ((int32_t) in[0]);
output[9] = ((limb) ((int32_t) in2[4])) * ((int32_t) in[5]) +
((limb) ((int32_t) in2[5])) * ((int32_t) in[4]) +
((limb) ((int32_t) in2[3])) * ((int32_t) in[6]) +
((limb) ((int32_t) in2[6])) * ((int32_t) in[3]) +
((limb) ((int32_t) in2[2])) * ((int32_t) in[7]) +
((limb) ((int32_t) in2[7])) * ((int32_t) in[2]) +
((limb) ((int32_t) in2[1])) * ((int32_t) in[8]) +
((limb) ((int32_t) in2[8])) * ((int32_t) in[1]) +
((limb) ((int32_t) in2[0])) * ((int32_t) in[9]) +
((limb) ((int32_t) in2[9])) * ((int32_t) in[0]);
output[10] = 2 * (((limb) ((int32_t) in2[5])) * ((int32_t) in[5]) +
((limb) ((int32_t) in2[3])) * ((int32_t) in[7]) +
((limb) ((int32_t) in2[7])) * ((int32_t) in[3]) +
((limb) ((int32_t) in2[1])) * ((int32_t) in[9]) +
((limb) ((int32_t) in2[9])) * ((int32_t) in[1])) +
((limb) ((int32_t) in2[4])) * ((int32_t) in[6]) +
((limb) ((int32_t) in2[6])) * ((int32_t) in[4]) +
((limb) ((int32_t) in2[2])) * ((int32_t) in[8]) +
((limb) ((int32_t) in2[8])) * ((int32_t) in[2]);
output[11] = ((limb) ((int32_t) in2[5])) * ((int32_t) in[6]) +
((limb) ((int32_t) in2[6])) * ((int32_t) in[5]) +
((limb) ((int32_t) in2[4])) * ((int32_t) in[7]) +
((limb) ((int32_t) in2[7])) * ((int32_t) in[4]) +
((limb) ((int32_t) in2[3])) * ((int32_t) in[8]) +
((limb) ((int32_t) in2[8])) * ((int32_t) in[3]) +
((limb) ((int32_t) in2[2])) * ((int32_t) in[9]) +
((limb) ((int32_t) in2[9])) * ((int32_t) in[2]);
output[12] = ((limb) ((int32_t) in2[6])) * ((int32_t) in[6]) +
2 * (((limb) ((int32_t) in2[5])) * ((int32_t) in[7]) +
((limb) ((int32_t) in2[7])) * ((int32_t) in[5]) +
((limb) ((int32_t) in2[3])) * ((int32_t) in[9]) +
((limb) ((int32_t) in2[9])) * ((int32_t) in[3])) +
((limb) ((int32_t) in2[4])) * ((int32_t) in[8]) +
((limb) ((int32_t) in2[8])) * ((int32_t) in[4]);
output[13] = ((limb) ((int32_t) in2[6])) * ((int32_t) in[7]) +
((limb) ((int32_t) in2[7])) * ((int32_t) in[6]) +
((limb) ((int32_t) in2[5])) * ((int32_t) in[8]) +
((limb) ((int32_t) in2[8])) * ((int32_t) in[5]) +
((limb) ((int32_t) in2[4])) * ((int32_t) in[9]) +
((limb) ((int32_t) in2[9])) * ((int32_t) in[4]);
output[14] = 2 * (((limb) ((int32_t) in2[7])) * ((int32_t) in[7]) +
((limb) ((int32_t) in2[5])) * ((int32_t) in[9]) +
((limb) ((int32_t) in2[9])) * ((int32_t) in[5])) +
((limb) ((int32_t) in2[6])) * ((int32_t) in[8]) +
((limb) ((int32_t) in2[8])) * ((int32_t) in[6]);
output[15] = ((limb) ((int32_t) in2[7])) * ((int32_t) in[8]) +
((limb) ((int32_t) in2[8])) * ((int32_t) in[7]) +
((limb) ((int32_t) in2[6])) * ((int32_t) in[9]) +
((limb) ((int32_t) in2[9])) * ((int32_t) in[6]);
output[16] = ((limb) ((int32_t) in2[8])) * ((int32_t) in[8]) +
2 * (((limb) ((int32_t) in2[7])) * ((int32_t) in[9]) +
((limb) ((int32_t) in2[9])) * ((int32_t) in[7]));
output[17] = ((limb) ((int32_t) in2[8])) * ((int32_t) in[9]) +
((limb) ((int32_t) in2[9])) * ((int32_t) in[8]);
output[18] = 2 * ((limb) ((int32_t) in2[9])) * ((int32_t) in[9]);
}
/* Reduce a long form to a short form by taking the input mod 2^255 - 19.
*
* On entry: |output[i]| < 14*2^54
* On exit: |output[0..8]| < 280*2^54
*/
static void freduce_degree(limb *output)
{
/* Each of these shifts and adds ends up multiplying the value by 19.
*
* For output[0..8], the absolute entry value is < 14*2^54 and we add, at
* most, 19*14*2^54 thus, on exit, |output[0..8]| < 280*2^54.
*/
output[8] += output[18] << 4;
output[8] += output[18] << 1;
output[8] += output[18];
output[7] += output[17] << 4;
output[7] += output[17] << 1;
output[7] += output[17];
output[6] += output[16] << 4;
output[6] += output[16] << 1;
output[6] += output[16];
output[5] += output[15] << 4;
output[5] += output[15] << 1;
output[5] += output[15];
output[4] += output[14] << 4;
output[4] += output[14] << 1;
output[4] += output[14];
output[3] += output[13] << 4;
output[3] += output[13] << 1;
output[3] += output[13];
output[2] += output[12] << 4;
output[2] += output[12] << 1;
output[2] += output[12];
output[1] += output[11] << 4;
output[1] += output[11] << 1;
output[1] += output[11];
output[0] += output[10] << 4;
output[0] += output[10] << 1;
output[0] += output[10];
}
#if (-1 & 3) != 3
#error "This code only works on a two's complement system"
#endif
/* return v / 2^26, using only shifts and adds.
*
* On entry: v can take any value.
*/
static inline limb div_by_2_26(const limb v)
{
/* High word of v; no shift needed. */
const uint32_t highword = (uint32_t) (((uint64_t) v) >> 32);
/* Set to all 1s if v was negative; else set to 0s. */
const int32_t sign = ((int32_t) highword) >> 31;
/* Set to 0x3ffffff if v was negative; else set to 0. */
const int32_t roundoff = ((uint32_t) sign) >> 6;
/* Should return v / (1<<26) */
return (v + roundoff) >> 26;
}
/* return v / (2^25), using only shifts and adds.
*
* On entry: v can take any value.
*/
static inline limb div_by_2_25(const limb v)
{
/* High word of v; no shift needed*/
const uint32_t highword = (uint32_t) (((uint64_t) v) >> 32);
/* Set to all 1s if v was negative; else set to 0s. */
const int32_t sign = ((int32_t) highword) >> 31;
/* Set to 0x1ffffff if v was negative; else set to 0. */
const int32_t roundoff = ((uint32_t) sign) >> 7;
/* Should return v / (1<<25) */
return (v + roundoff) >> 25;
}
/* Reduce all coefficients of the short form input so that |x| < 2^26.
*
* On entry: |output[i]| < 280*2^54
*/
static void freduce_coefficients(limb *output)
{
unsigned int i;
output[10] = 0;
for (i = 0; i < 10; i += 2) {
limb over = div_by_2_26(output[i]);
/* The entry condition (that |output[i]| < 280*2^54) means that over is, at
* most, 280*2^28 in the first iteration of this loop. This is added to the
* next limb and we can approximate the resulting bound of that limb by
* 281*2^54.
*/
output[i] -= over << 26;
output[i+1] += over;
/* For the first iteration, |output[i+1]| < 281*2^54, thus |over| <
* 281*2^29. When this is added to the next limb, the resulting bound can
* be approximated as 281*2^54.
*
* For subsequent iterations of the loop, 281*2^54 remains a conservative
* bound and no overflow occurs.
*/
over = div_by_2_25(output[i+1]);
output[i+1] -= over << 25;
output[i+2] += over;
}
/* Now |output[10]| < 281*2^29 and all other coefficients are reduced. */
output[0] += output[10] << 4;
output[0] += output[10] << 1;
output[0] += output[10];
output[10] = 0;
/* Now output[1..9] are reduced, and |output[0]| < 2^26 + 19*281*2^29
* So |over| will be no more than 2^16.
*/
{
limb over = div_by_2_26(output[0]);
output[0] -= over << 26;
output[1] += over;
}
/* Now output[0,2..9] are reduced, and |output[1]| < 2^25 + 2^16 < 2^26. The
* bound on |output[1]| is sufficient to meet our needs.
*/
}
/* A helpful wrapper around fproduct: output = in * in2.
*
* On entry: |in[i]| < 2^27 and |in2[i]| < 2^27.
*
* output must be distinct to both inputs. The output is reduced degree
* (indeed, one need only provide storage for 10 limbs) and |output[i]| < 2^26.
*/
static void fmul(limb *output, const limb *in, const limb *in2)
{
limb t[19];
fproduct(t, in, in2);
/* |t[i]| < 14*2^54 */
freduce_degree(t);
freduce_coefficients(t);
/* |t[i]| < 2^26 */
__builtin_memcpy(output, t, sizeof(limb) * 10);
}
/* Square a number: output = in**2
*
* output must be distinct from the input. The inputs are reduced coefficient
* form, the output is not.
*
* output[x] <= 14 * the largest product of the input limbs.
*/
static void fsquare_inner(limb *output, const limb *in)
{
output[0] = ((limb) ((int32_t) in[0])) * ((int32_t) in[0]);
output[1] = 2 * ((limb) ((int32_t) in[0])) * ((int32_t) in[1]);
output[2] = 2 * (((limb) ((int32_t) in[1])) * ((int32_t) in[1]) +
((limb) ((int32_t) in[0])) * ((int32_t) in[2]));
output[3] = 2 * (((limb) ((int32_t) in[1])) * ((int32_t) in[2]) +
((limb) ((int32_t) in[0])) * ((int32_t) in[3]));
output[4] = ((limb) ((int32_t) in[2])) * ((int32_t) in[2]) +
4 * ((limb) ((int32_t) in[1])) * ((int32_t) in[3]) +
2 * ((limb) ((int32_t) in[0])) * ((int32_t) in[4]);
output[5] = 2 * (((limb) ((int32_t) in[2])) * ((int32_t) in[3]) +
((limb) ((int32_t) in[1])) * ((int32_t) in[4]) +
((limb) ((int32_t) in[0])) * ((int32_t) in[5]));
output[6] = 2 * (((limb) ((int32_t) in[3])) * ((int32_t) in[3]) +
((limb) ((int32_t) in[2])) * ((int32_t) in[4]) +
((limb) ((int32_t) in[0])) * ((int32_t) in[6]) +
2 * ((limb) ((int32_t) in[1])) * ((int32_t) in[5]));
output[7] = 2 * (((limb) ((int32_t) in[3])) * ((int32_t) in[4]) +
((limb) ((int32_t) in[2])) * ((int32_t) in[5]) +
((limb) ((int32_t) in[1])) * ((int32_t) in[6]) +
((limb) ((int32_t) in[0])) * ((int32_t) in[7]));
output[8] = ((limb) ((int32_t) in[4])) * ((int32_t) in[4]) +
2 * (((limb) ((int32_t) in[2])) * ((int32_t) in[6]) +
((limb) ((int32_t) in[0])) * ((int32_t) in[8]) +
2 * (((limb) ((int32_t) in[1])) * ((int32_t) in[7]) +
((limb) ((int32_t) in[3])) * ((int32_t) in[5])));
output[9] = 2 * (((limb) ((int32_t) in[4])) * ((int32_t) in[5]) +
((limb) ((int32_t) in[3])) * ((int32_t) in[6]) +
((limb) ((int32_t) in[2])) * ((int32_t) in[7]) +
((limb) ((int32_t) in[1])) * ((int32_t) in[8]) +
((limb) ((int32_t) in[0])) * ((int32_t) in[9]));
output[10] = 2 * (((limb) ((int32_t) in[5])) * ((int32_t) in[5]) +
((limb) ((int32_t) in[4])) * ((int32_t) in[6]) +
((limb) ((int32_t) in[2])) * ((int32_t) in[8]) +
2 * (((limb) ((int32_t) in[3])) * ((int32_t) in[7]) +
((limb) ((int32_t) in[1])) * ((int32_t) in[9])));
output[11] = 2 * (((limb) ((int32_t) in[5])) * ((int32_t) in[6]) +
((limb) ((int32_t) in[4])) * ((int32_t) in[7]) +
((limb) ((int32_t) in[3])) * ((int32_t) in[8]) +
((limb) ((int32_t) in[2])) * ((int32_t) in[9]));
output[12] = ((limb) ((int32_t) in[6])) * ((int32_t) in[6]) +
2 * (((limb) ((int32_t) in[4])) * ((int32_t) in[8]) +
2 * (((limb) ((int32_t) in[5])) * ((int32_t) in[7]) +
((limb) ((int32_t) in[3])) * ((int32_t) in[9])));
output[13] = 2 * (((limb) ((int32_t) in[6])) * ((int32_t) in[7]) +
((limb) ((int32_t) in[5])) * ((int32_t) in[8]) +
((limb) ((int32_t) in[4])) * ((int32_t) in[9]));
output[14] = 2 * (((limb) ((int32_t) in[7])) * ((int32_t) in[7]) +
((limb) ((int32_t) in[6])) * ((int32_t) in[8]) +
2 * ((limb) ((int32_t) in[5])) * ((int32_t) in[9]));
output[15] = 2 * (((limb) ((int32_t) in[7])) * ((int32_t) in[8]) +
((limb) ((int32_t) in[6])) * ((int32_t) in[9]));
output[16] = ((limb) ((int32_t) in[8])) * ((int32_t) in[8]) +
4 * ((limb) ((int32_t) in[7])) * ((int32_t) in[9]);
output[17] = 2 * ((limb) ((int32_t) in[8])) * ((int32_t) in[9]);
output[18] = 2 * ((limb) ((int32_t) in[9])) * ((int32_t) in[9]);
}
/* fsquare sets output = in^2.
*
* On entry: The |in| argument is in reduced coefficients form and |in[i]| <
* 2^27.
*
* On exit: The |output| argument is in reduced coefficients form (indeed, one
* need only provide storage for 10 limbs) and |out[i]| < 2^26.
*/
static void fsquare(limb *output, const limb *in)
{
limb t[19];
fsquare_inner(t, in);
/* |t[i]| < 14*2^54 because the largest product of two limbs will be <
* 2^(27+27) and fsquare_inner adds together, at most, 14 of those
* products.
*/
freduce_degree(t);
freduce_coefficients(t);
/* |t[i]| < 2^26 */
__builtin_memcpy(output, t, sizeof(limb) * 10);
}
/* Take a little-endian, 32-byte number and expand it into polynomial form */
static void fexpand(limb *output, const uint8_t *input)
{
#define F(n, start, shift, mask) \
output[n] = ((((limb) input[start + 0]) | \
((limb) input[start + 1]) << 8 | \
((limb) input[start + 2]) << 16 | \
((limb) input[start + 3]) << 24) >> shift) & mask;
F(0, 0, 0, 0x3ffffff);
F(1, 3, 2, 0x1ffffff);
F(2, 6, 3, 0x3ffffff);
F(3, 9, 5, 0x1ffffff);
F(4, 12, 6, 0x3ffffff);
F(5, 16, 0, 0x1ffffff);
F(6, 19, 1, 0x3ffffff);
F(7, 22, 3, 0x1ffffff);
F(8, 25, 4, 0x3ffffff);
F(9, 28, 6, 0x1ffffff);
#undef F
}
#if (-32 >> 1) != -16
#error "This code only works when >> does sign-extension on negative numbers"
#endif
/* int32_t_eq returns 0xffffffff iff a == b and zero otherwise. */
static int32_t int32_t_eq(int32_t a, int32_t b)
{
a = ~(a ^ b);
a &= a << 16;
a &= a << 8;
a &= a << 4;
a &= a << 2;
a &= a << 1;
return a >> 31;
}
/* int32_t_gte returns 0xffffffff if a >= b and zero otherwise, where a and b are
* both non-negative.
*/
static int32_t int32_t_gte(int32_t a, int32_t b)
{
a -= b;
/* a >= 0 iff a >= b. */
return ~(a >> 31);
}
/* Take a fully reduced polynomial form number and contract it into a
* little-endian, 32-byte array.
*
* On entry: |input_limbs[i]| < 2^26
*/
static void fcontract(uint8_t *output, limb *input_limbs)
{
int i;
int j;
int32_t input[10];
int32_t mask;
/* |input_limbs[i]| < 2^26, so it's valid to convert to an int32_t. */
for (i = 0; i < 10; i++) {
input[i] = input_limbs[i];
}
for (j = 0; j < 2; ++j) {
for (i = 0; i < 9; ++i) {
if ((i & 1) == 1) {
/* This calculation is a time-invariant way to make input[i]
* non-negative by borrowing from the next-larger limb.
*/
const int32_t mask = input[i] >> 31;
const int32_t carry = -((input[i] & mask) >> 25);
input[i] = input[i] + (carry << 25);
input[i+1] = input[i+1] - carry;
} else {
const int32_t mask = input[i] >> 31;
const int32_t carry = -((input[i] & mask) >> 26);
input[i] = input[i] + (carry << 26);
input[i+1] = input[i+1] - carry;
}
}
/* There's no greater limb for input[9] to borrow from, but we can multiply
* by 19 and borrow from input[0], which is valid mod 2^255-19.
*/
{
const int32_t mask = input[9] >> 31;
const int32_t carry = -((input[9] & mask) >> 25);
input[9] = input[9] + (carry << 25);
input[0] = input[0] - (carry * 19);
}
/* After the first iteration, input[1..9] are non-negative and fit within
* 25 or 26 bits, depending on position. However, input[0] may be
* negative.
*/
}
/* The first borrow-propagation pass above ended with every limb
except (possibly) input[0] non-negative.
If input[0] was negative after the first pass, then it was because of a
carry from input[9]. On entry, input[9] < 2^26 so the carry was, at most,
one, since (2**26-1) >> 25 = 1. Thus input[0] >= -19.
In the second pass, each limb is decreased by at most one. Thus the second
borrow-propagation pass could only have wrapped around to decrease
input[0] again if the first pass left input[0] negative *and* input[1]
through input[9] were all zero. In that case, input[1] is now 2^25 - 1,
and this last borrow-propagation step will leave input[1] non-negative. */
{
const int32_t mask = input[0] >> 31;
const int32_t carry = -((input[0] & mask) >> 26);
input[0] = input[0] + (carry << 26);
input[1] = input[1] - carry;
}
/* All input[i] are now non-negative. However, there might be values between
* 2^25 and 2^26 in a limb which is, nominally, 25 bits wide.
*/
for (j = 0; j < 2; j++) {
for (i = 0; i < 9; i++) {
if ((i & 1) == 1) {
const int32_t carry = input[i] >> 25;
input[i] &= 0x1ffffff;
input[i+1] += carry;
} else {
const int32_t carry = input[i] >> 26;
input[i] &= 0x3ffffff;
input[i+1] += carry;
}
}
{
const int32_t carry = input[9] >> 25;
input[9] &= 0x1ffffff;
input[0] += 19*carry;
}
}
/* If the first carry-chain pass, just above, ended up with a carry from
* input[9], and that caused input[0] to be out-of-bounds, then input[0] was
* < 2^26 + 2*19, because the carry was, at most, two.
*
* If the second pass carried from input[9] again then input[0] is < 2*19 and
* the input[9] -> input[0] carry didn't push input[0] out of bounds.
*/
/* It still remains the case that input might be between 2^255-19 and 2^255.
* In this case, input[1..9] must take their maximum value and input[0] must
* be >= (2^255-19) & 0x3ffffff, which is 0x3ffffed.
*/
mask = int32_t_gte(input[0], 0x3ffffed);
for (i = 1; i < 10; i++) {
if ((i & 1) == 1) {
mask &= int32_t_eq(input[i], 0x1ffffff);
} else {
mask &= int32_t_eq(input[i], 0x3ffffff);
}
}
/* mask is either 0xffffffff (if input >= 2^255-19) and zero otherwise. Thus
* this conditionally subtracts 2^255-19.
*/
input[0] -= mask & 0x3ffffed;
for (i = 1; i < 10; i++) {
if ((i & 1) == 1) {
input[i] -= mask & 0x1ffffff;
} else {
input[i] -= mask & 0x3ffffff;
}
}
input[1] <<= 2;
input[2] <<= 3;
input[3] <<= 5;
input[4] <<= 6;
input[6] <<= 1;
input[7] <<= 3;
input[8] <<= 4;
input[9] <<= 6;
#define F(i, s) \
output[s+0] |= input[i] & 0xff; \
output[s+1] = (input[i] >> 8) & 0xff; \
output[s+2] = (input[i] >> 16) & 0xff; \
output[s+3] = (input[i] >> 24) & 0xff;
output[0] = 0;
output[16] = 0;
F(0, 0);
F(1, 3);
F(2, 6);
F(3, 9);
F(4, 12);
F(5, 16);
F(6, 19);
F(7, 22);
F(8, 25);
F(9, 28);
#undef F
}
/* Input: Q, Q', Q-Q'
* Output: 2Q, Q+Q'
*
* x2 z3: long form
* x3 z3: long form
* x z: short form, destroyed
* xprime zprime: short form, destroyed
* qmqp: short form, preserved
*
* On entry and exit, the absolute value of the limbs of all inputs and outputs
* are < 2^26.
*/
static void fmonty(limb *x2, limb *z2, /* output 2Q */
limb *x3, limb *z3, /* output Q + Q' */
limb *x, limb *z, /* input Q */
limb *xprime, limb *zprime, /* input Q' */
const limb *qmqp /* input Q - Q' */)
{
limb origx[10], origxprime[10], zzz[19], xx[19], zz[19], xxprime[19],
zzprime[19], zzzprime[19], xxxprime[19];
__builtin_memcpy(origx, x, 10 * sizeof(limb));
fsum(x, z);
/* |x[i]| < 2^27 */
fdifference(z, origx); /* does x - z */
/* |z[i]| < 2^27 */
__builtin_memcpy(origxprime, xprime, sizeof(limb) * 10);
fsum(xprime, zprime);
/* |xprime[i]| < 2^27 */
fdifference(zprime, origxprime);
/* |zprime[i]| < 2^27 */
fproduct(xxprime, xprime, z);
/* |xxprime[i]| < 14*2^54: the largest product of two limbs will be <
* 2^(27+27) and fproduct adds together, at most, 14 of those products.
* (Approximating that to 2^58 doesn't work out.)
*/
fproduct(zzprime, x, zprime);
/* |zzprime[i]| < 14*2^54 */
freduce_degree(xxprime);
freduce_coefficients(xxprime);
/* |xxprime[i]| < 2^26 */
freduce_degree(zzprime);
freduce_coefficients(zzprime);
/* |zzprime[i]| < 2^26 */
__builtin_memcpy(origxprime, xxprime, sizeof(limb) * 10);
fsum(xxprime, zzprime);
/* |xxprime[i]| < 2^27 */
fdifference(zzprime, origxprime);
/* |zzprime[i]| < 2^27 */
fsquare(xxxprime, xxprime);
/* |xxxprime[i]| < 2^26 */
fsquare(zzzprime, zzprime);
/* |zzzprime[i]| < 2^26 */
fproduct(zzprime, zzzprime, qmqp);
/* |zzprime[i]| < 14*2^52 */
freduce_degree(zzprime);
freduce_coefficients(zzprime);
/* |zzprime[i]| < 2^26 */
__builtin_memcpy(x3, xxxprime, sizeof(limb) * 10);
__builtin_memcpy(z3, zzprime, sizeof(limb) * 10);
fsquare(xx, x);
/* |xx[i]| < 2^26 */
fsquare(zz, z);
/* |zz[i]| < 2^26 */
fproduct(x2, xx, zz);
/* |x2[i]| < 14*2^52 */
freduce_degree(x2);
freduce_coefficients(x2);
/* |x2[i]| < 2^26 */
fdifference(zz, xx); // does zz = xx - zz
/* |zz[i]| < 2^27 */
__builtin_memset(zzz + 10, 0, sizeof(limb) * 9);
fscalar_product(zzz, zz, 121665);
/* |zzz[i]| < 2^(27+17) */
/* No need to call freduce_degree here:
fscalar_product doesn't increase the degree of its input. */
freduce_coefficients(zzz);
/* |zzz[i]| < 2^26 */
fsum(zzz, xx);
/* |zzz[i]| < 2^27 */
fproduct(z2, zz, zzz);
/* |z2[i]| < 14*2^(26+27) */
freduce_degree(z2);
freduce_coefficients(z2);
/* |z2|i| < 2^26 */
}
/* Conditionally swap two reduced-form limb arrays if 'iswap' is 1, but leave
* them unchanged if 'iswap' is 0. Runs in data-invariant time to avoid
* side-channel attacks.
*
* NOTE that this function requires that 'iswap' be 1 or 0; other values give
* wrong results. Also, the two limb arrays must be in reduced-coefficient,
* reduced-degree form: the values in a[10..19] or b[10..19] aren't swapped,
* and all all values in a[0..9],b[0..9] must have magnitude less than
* INT32_MAX.
*/
static void swap_conditional(limb a[static 19], limb b[static 19], limb iswap)
{
unsigned int i;
const int32_t swap = (int32_t) -iswap;
for (i = 0; i < 10; ++i) {
const int32_t x = swap & (((int32_t)a[i]) ^ ((int32_t)b[i]));
a[i] = ((int32_t)a[i]) ^ x;
b[i] = ((int32_t)b[i]) ^ x;
}
}
/* Calculates nQ where Q is the x-coordinate of a point on the curve
*
* resultx/resultz: the x coordinate of the resulting curve point (short form)
* n: a little endian, 32-byte number
* q: a point of the curve (short form)
*/
static void cmult(limb *resultx, limb *resultz, const uint8_t *n, const limb *q)
{
limb a[19] = {0}, b[19] = {1}, c[19] = {1}, d[19] = {0};
limb *nqpqx = a, *nqpqz = b, *nqx = c, *nqz = d, *t;
limb e[19] = {0}, f[19] = {1}, g[19] = {0}, h[19] = {1};
limb *nqpqx2 = e, *nqpqz2 = f, *nqx2 = g, *nqz2 = h;
unsigned int i, j;
__builtin_memcpy(nqpqx, q, sizeof(limb) * 10);
for (i = 0; i < 32; ++i) {
uint8_t byte = n[31 - i];
for (j = 0; j < 8; ++j) {
const limb bit = byte >> 7;
swap_conditional(nqx, nqpqx, bit);
swap_conditional(nqz, nqpqz, bit);
fmonty(nqx2, nqz2,
nqpqx2, nqpqz2,
nqx, nqz,
nqpqx, nqpqz,
q);
swap_conditional(nqx2, nqpqx2, bit);
swap_conditional(nqz2, nqpqz2, bit);
t = nqx;
nqx = nqx2;
nqx2 = t;
t = nqz;
nqz = nqz2;
nqz2 = t;
t = nqpqx;
nqpqx = nqpqx2;
nqpqx2 = t;
t = nqpqz;
nqpqz = nqpqz2;
nqpqz2 = t;
byte <<= 1;
}
}
__builtin_memcpy(resultx, nqx, sizeof(limb) * 10);
__builtin_memcpy(resultz, nqz, sizeof(limb) * 10);
}
static void crecip(limb *out, const limb *z)
{
limb z2[10];
limb z9[10];
limb z11[10];
limb z2_5_0[10];
limb z2_10_0[10];
limb z2_20_0[10];
limb z2_50_0[10];
limb z2_100_0[10];
limb t0[10];
limb t1[10];
int i;
/* 2 */ fsquare(z2, z);
/* 4 */ fsquare(t1, z2);
/* 8 */ fsquare(t0, t1);
/* 9 */ fmul(z9, t0, z);
/* 11 */ fmul(z11, z9, z2);
/* 22 */ fsquare(t0, z11);
/* 2^5 - 2^0 = 31 */ fmul(z2_5_0, t0, z9);
/* 2^6 - 2^1 */ fsquare(t0, z2_5_0);
/* 2^7 - 2^2 */ fsquare(t1, t0);
/* 2^8 - 2^3 */ fsquare(t0, t1);
/* 2^9 - 2^4 */ fsquare(t1, t0);
/* 2^10 - 2^5 */ fsquare(t0, t1);
/* 2^10 - 2^0 */ fmul(z2_10_0, t0, z2_5_0);
/* 2^11 - 2^1 */ fsquare(t0, z2_10_0);
/* 2^12 - 2^2 */ fsquare(t1, t0);
/* 2^20 - 2^10 */ for (i = 2; i < 10; i += 2) { fsquare(t0, t1); fsquare(t1, t0); }
/* 2^20 - 2^0 */ fmul(z2_20_0, t1, z2_10_0);
/* 2^21 - 2^1 */ fsquare(t0, z2_20_0);
/* 2^22 - 2^2 */ fsquare(t1, t0);
/* 2^40 - 2^20 */ for (i = 2; i < 20; i += 2) { fsquare(t0, t1); fsquare(t1, t0); }
/* 2^40 - 2^0 */ fmul(t0, t1, z2_20_0);
/* 2^41 - 2^1 */ fsquare(t1, t0);
/* 2^42 - 2^2 */ fsquare(t0, t1);
/* 2^50 - 2^10 */ for (i = 2; i < 10; i += 2) { fsquare(t1, t0); fsquare(t0, t1); }
/* 2^50 - 2^0 */ fmul(z2_50_0, t0, z2_10_0);
/* 2^51 - 2^1 */ fsquare(t0, z2_50_0);
/* 2^52 - 2^2 */ fsquare(t1, t0);
/* 2^100 - 2^50 */ for (i = 2; i < 50; i += 2) { fsquare(t0, t1); fsquare(t1, t0); }
/* 2^100 - 2^0 */ fmul(z2_100_0, t1, z2_50_0);
/* 2^101 - 2^1 */ fsquare(t1, z2_100_0);
/* 2^102 - 2^2 */ fsquare(t0, t1);
/* 2^200 - 2^100 */ for (i = 2; i < 100; i += 2) { fsquare(t1, t0); fsquare(t0, t1); }
/* 2^200 - 2^0 */ fmul(t1, t0, z2_100_0);
/* 2^201 - 2^1 */ fsquare(t0, t1);
/* 2^202 - 2^2 */ fsquare(t1, t0);
/* 2^250 - 2^50 */ for (i = 2; i < 50; i += 2) { fsquare(t0, t1); fsquare(t1, t0); }
/* 2^250 - 2^0 */ fmul(t0, t1, z2_50_0);
/* 2^251 - 2^1 */ fsquare(t1, t0);
/* 2^252 - 2^2 */ fsquare(t0, t1);
/* 2^253 - 2^3 */ fsquare(t1, t0);
/* 2^254 - 2^4 */ fsquare(t0, t1);
/* 2^255 - 2^5 */ fsquare(t1, t0);
/* 2^255 - 21 */ fmul(out, t1, z11);
}
static inline void curve25519_normalize_secret(uint8_t secret[static 32])
{
secret[0] &= 248;
secret[31] &= 127;
secret[31] |= 64;
}
static inline void curve25519(uint8_t mypublic[static 32], const uint8_t secret[static 32], const uint8_t basepoint[static 32])
{
limb bp[10], x[10], z[11], zmone[10];
uint8_t e[32];
__builtin_memcpy(e, secret, 32);
curve25519_normalize_secret(e);
fexpand(bp, basepoint);
cmult(x, z, e, bp);
crecip(zmone, z);
fmul(z, x, zmone);
fcontract(mypublic, z);
}
EMSCRIPTEN_KEEPALIVE void curve25519_generate_public(uint8_t public[static 32], const uint8_t private[static 32])
{
static const uint8_t basepoint[32] = { 9 };
curve25519(public, private, basepoint);
}
EMSCRIPTEN_KEEPALIVE void curve25519_generate_private(uint8_t private[static 32])
{
int i;
EM_ASM({
/* Same trick as libsodium */
var getRandomValue = function() {
var buf = new Uint32Array(1);
window.crypto.getRandomValues(buf);
return buf[0] >>> 0;
};
Module.getRandomValue = getRandomValue;
});
for (i = 0; i < 32; ++i)
private[i] = EM_ASM_INT_V({ return Module.getRandomValue(); });
curve25519_normalize_secret(private);
}
static inline void encode_base64(char dest[4], const uint8_t src[3])
{
const uint8_t input[] = { (src[0] >> 2) & 63, ((src[0] << 4) | (src[1] >> 4)) & 63, ((src[1] << 2) | (src[2] >> 6)) & 63, src[2] & 63 };
for (unsigned int i = 0; i < 4; ++i)
dest[i] = input[i] + 'A'
+ (((25 - input[i]) >> 8) & 6)
- (((51 - input[i]) >> 8) & 75)
- (((61 - input[i]) >> 8) & 15)
+ (((62 - input[i]) >> 8) & 3);
}
EMSCRIPTEN_KEEPALIVE void key_to_base64(char base64[static 45], const uint8_t key[static 32])
{
unsigned int i;
for (i = 0; i < 32 / 3; ++i)
encode_base64(&base64[i * 4], &key[i * 3]);
encode_base64(&base64[i * 4], (const uint8_t[]){ key[i * 3 + 0], key[i * 3 + 1], 0 });
base64[45 - 2] = '=';
base64[45 - 1] = '\0';
}