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/*
* SPDX-FileCopyrightText: 2022-2023 Espressif Systems (Shanghai) CO LTD
*
* SPDX-License-Identifier: Apache-2.0
*/
// This file contains SRP6a implementation based on RFC 5054
#include <string.h>
#include "esp_log.h"
#include "esp_err.h"
#include <mbedtls/sha512.h>
#include "esp_srp_mpi.h"
#include "esp_srp.h"
#define SHA512_HASH_SZ 64
static const char *TAG = "srp6a";
typedef struct esp_srp_handle {
esp_ng_type_t type;
esp_mpi_ctx_t *ctx;
/* N
* the bytes_n simply points to the static array
*/
esp_mpi_t *n;
const char *bytes_n;
int len_n;
/* g
* the bytes_g simply points to the static array
*/
esp_mpi_t *g;
const char *bytes_g;
int len_g;
/* Salt */
esp_mpi_t *s;
char *bytes_s;
int len_s;
/* Verifier */
esp_mpi_t *v;
/* B */
esp_mpi_t *B;
char *bytes_B;
int len_B;
/* b */
esp_mpi_t *b;
/* A */
esp_mpi_t *A;
char *bytes_A;
int len_A;
/* K - session key*/
char *session_key;
} esp_srp_handle;
static void hexdump_mpi(const char *name, esp_mpi_t *bn)
{
int len = 0;
char *str = esp_mpi_to_bin(bn, &len);
if (str) {
ESP_LOGD(TAG, "%s ->", name);
ESP_LOG_BUFFER_HEX_LEVEL(TAG, str, len, ESP_LOG_DEBUG);
free(str);
}
}
/************************* SRP Stuff *************************/
static const char N_3072[] = {
0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xC9, 0x0F, 0xDA, 0xA2, 0x21, 0x68, 0xC2, 0x34,
0xC4, 0xC6, 0x62, 0x8B, 0x80, 0xDC, 0x1C, 0xD1, 0x29, 0x02, 0x4E, 0x08, 0x8A, 0x67, 0xCC, 0x74,
0x02, 0x0B, 0xBE, 0xA6, 0x3B, 0x13, 0x9B, 0x22, 0x51, 0x4A, 0x08, 0x79, 0x8E, 0x34, 0x04, 0xDD,
0xEF, 0x95, 0x19, 0xB3, 0xCD, 0x3A, 0x43, 0x1B, 0x30, 0x2B, 0x0A, 0x6D, 0xF2, 0x5F, 0x14, 0x37,
0x4F, 0xE1, 0x35, 0x6D, 0x6D, 0x51, 0xC2, 0x45, 0xE4, 0x85, 0xB5, 0x76, 0x62, 0x5E, 0x7E, 0xC6,
0xF4, 0x4C, 0x42, 0xE9, 0xA6, 0x37, 0xED, 0x6B, 0x0B, 0xFF, 0x5C, 0xB6, 0xF4, 0x06, 0xB7, 0xED,
0xEE, 0x38, 0x6B, 0xFB, 0x5A, 0x89, 0x9F, 0xA5, 0xAE, 0x9F, 0x24, 0x11, 0x7C, 0x4B, 0x1F, 0xE6,
0x49, 0x28, 0x66, 0x51, 0xEC, 0xE4, 0x5B, 0x3D, 0xC2, 0x00, 0x7C, 0xB8, 0xA1, 0x63, 0xBF, 0x05,
0x98, 0xDA, 0x48, 0x36, 0x1C, 0x55, 0xD3, 0x9A, 0x69, 0x16, 0x3F, 0xA8, 0xFD, 0x24, 0xCF, 0x5F,
0x83, 0x65, 0x5D, 0x23, 0xDC, 0xA3, 0xAD, 0x96, 0x1C, 0x62, 0xF3, 0x56, 0x20, 0x85, 0x52, 0xBB,
0x9E, 0xD5, 0x29, 0x07, 0x70, 0x96, 0x96, 0x6D, 0x67, 0x0C, 0x35, 0x4E, 0x4A, 0xBC, 0x98, 0x04,
0xF1, 0x74, 0x6C, 0x08, 0xCA, 0x18, 0x21, 0x7C, 0x32, 0x90, 0x5E, 0x46, 0x2E, 0x36, 0xCE, 0x3B,
0xE3, 0x9E, 0x77, 0x2C, 0x18, 0x0E, 0x86, 0x03, 0x9B, 0x27, 0x83, 0xA2, 0xEC, 0x07, 0xA2, 0x8F,
0xB5, 0xC5, 0x5D, 0xF0, 0x6F, 0x4C, 0x52, 0xC9, 0xDE, 0x2B, 0xCB, 0xF6, 0x95, 0x58, 0x17, 0x18,
0x39, 0x95, 0x49, 0x7C, 0xEA, 0x95, 0x6A, 0xE5, 0x15, 0xD2, 0x26, 0x18, 0x98, 0xFA, 0x05, 0x10,
0x15, 0x72, 0x8E, 0x5A, 0x8A, 0xAA, 0xC4, 0x2D, 0xAD, 0x33, 0x17, 0x0D, 0x04, 0x50, 0x7A, 0x33,
0xA8, 0x55, 0x21, 0xAB, 0xDF, 0x1C, 0xBA, 0x64, 0xEC, 0xFB, 0x85, 0x04, 0x58, 0xDB, 0xEF, 0x0A,
0x8A, 0xEA, 0x71, 0x57, 0x5D, 0x06, 0x0C, 0x7D, 0xB3, 0x97, 0x0F, 0x85, 0xA6, 0xE1, 0xE4, 0xC7,
0xAB, 0xF5, 0xAE, 0x8C, 0xDB, 0x09, 0x33, 0xD7, 0x1E, 0x8C, 0x94, 0xE0, 0x4A, 0x25, 0x61, 0x9D,
0xCE, 0xE3, 0xD2, 0x26, 0x1A, 0xD2, 0xEE, 0x6B, 0xF1, 0x2F, 0xFA, 0x06, 0xD9, 0x8A, 0x08, 0x64,
0xD8, 0x76, 0x02, 0x73, 0x3E, 0xC8, 0x6A, 0x64, 0x52, 0x1F, 0x2B, 0x18, 0x17, 0x7B, 0x20, 0x0C,
0xBB, 0xE1, 0x17, 0x57, 0x7A, 0x61, 0x5D, 0x6C, 0x77, 0x09, 0x88, 0xC0, 0xBA, 0xD9, 0x46, 0xE2,
0x08, 0xE2, 0x4F, 0xA0, 0x74, 0xE5, 0xAB, 0x31, 0x43, 0xDB, 0x5B, 0xFC, 0xE0, 0xFD, 0x10, 0x8E,
0x4B, 0x82, 0xD1, 0x20, 0xA9, 0x3A, 0xD2, 0xCA, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF
};
static const char g_3072[] = { 5 };
esp_srp_handle_t *esp_srp_init(esp_ng_type_t ng)
{
esp_srp_handle_t *hd = calloc(1, sizeof(esp_srp_handle));
if (!hd) {
return NULL;
}
hd->ctx = esp_mpi_ctx_new();
if (! hd->ctx) {
goto error;
}
if (ng != ESP_NG_3072) {
goto error;
}
hd->n = esp_mpi_new_from_bin(N_3072, sizeof(N_3072));
hd->bytes_n = N_3072;
hd->len_n = sizeof(N_3072);
if (! hd->n) {
goto error;
}
hd->g = esp_mpi_new_from_bin(g_3072, sizeof(g_3072));
hd->bytes_g = g_3072;
hd->len_g = sizeof(g_3072);
if (! hd->g) {
goto error;
}
hd->type = ng;
return hd;
error:
esp_srp_free(hd);
return NULL;
}
void esp_srp_free(esp_srp_handle_t *hd)
{
if (!hd) {
return;
}
if (hd->ctx) {
esp_mpi_ctx_free(hd->ctx);
}
if (hd->n) {
esp_mpi_free(hd->n);
}
if (hd->g) {
esp_mpi_free(hd->g);
}
if (hd->s) {
esp_mpi_free(hd->s);
}
if (hd->bytes_s) {
free(hd->bytes_s);
}
if (hd->v) {
esp_mpi_free(hd->v);
}
if (hd->B) {
esp_mpi_free(hd->B);
}
if (hd->bytes_B) {
free(hd->bytes_B);
}
if (hd->b) {
esp_mpi_free(hd->b);
}
if (hd->A) {
esp_mpi_free(hd->A);
}
if (hd->bytes_A) {
free(hd->bytes_A);
}
if (hd->session_key) {
free(hd->session_key);
}
free(hd);
}
static esp_mpi_t *calculate_x(char *bytes_salt, int salt_len, const char *username, int username_len, const char *pass, int pass_len)
{
unsigned char digest[SHA512_HASH_SZ];
mbedtls_sha512_context ctx;
ESP_LOGD(TAG, "Username: %s | Passphrase: %s | Passphrase length: %d", username, pass, pass_len);
mbedtls_sha512_init(&ctx);
mbedtls_sha512_starts(&ctx, 0);
mbedtls_sha512_update(&ctx, (unsigned char *)username, username_len);
mbedtls_sha512_update(&ctx, (unsigned char *)":", 1);
mbedtls_sha512_update(&ctx, (unsigned char *)pass, pass_len);
mbedtls_sha512_finish(&ctx, digest);
mbedtls_sha512_init(&ctx);
mbedtls_sha512_starts(&ctx, 0);
mbedtls_sha512_update(&ctx, (unsigned char *)bytes_salt, salt_len);
mbedtls_sha512_update(&ctx, digest, sizeof(digest));
mbedtls_sha512_finish(&ctx, digest);
mbedtls_sha512_free(&ctx);
return esp_mpi_new_from_bin((char *)digest, sizeof(digest));
}
static esp_mpi_t *calculate_padded_hash(esp_srp_handle_t *hd, const char *a, int len_a, const char *b, int len_b)
{
unsigned char digest[SHA512_HASH_SZ];
mbedtls_sha512_context ctx;
int pad_len;
char *s = NULL;
if (len_a > len_b) {
pad_len = hd->len_n - len_b;
} else {
pad_len = hd->len_n - len_a;
}
if (pad_len) {
s = malloc(pad_len);
if (s) {
memset(s, 0, pad_len);
}
}
mbedtls_sha512_init(&ctx);
mbedtls_sha512_starts(&ctx, 0);
/* PAD (a) */
if (s && (len_a != hd->len_n)) {
mbedtls_sha512_update(&ctx, (unsigned char *)s, hd->len_n - len_a);
}
mbedtls_sha512_update(&ctx, (unsigned char *)a, len_a);
/* PAD (b) */
if (s && (len_b != hd->len_n)) {
mbedtls_sha512_update(&ctx, (unsigned char *)s, hd->len_n - len_b);
}
mbedtls_sha512_update(&ctx, (unsigned char *)b, len_b);
mbedtls_sha512_finish(&ctx, digest);
mbedtls_sha512_free(&ctx);
if (s) {
free(s);
}
return esp_mpi_new_from_bin((char *)digest, sizeof(digest));
}
/* k = SHA (N, PAD(g))
*
* https://tools.ietf.org/html/draft-ietf-tls-srp-08
*/
static esp_mpi_t *calculate_k(esp_srp_handle_t *hd)
{
return calculate_padded_hash(hd, hd->bytes_n, hd->len_n, hd->bytes_g, hd->len_g);
}
static esp_mpi_t *calculate_u(esp_srp_handle_t *hd, char *A, int len_A)
{
return calculate_padded_hash(hd, A, len_A, hd->bytes_B, hd->len_B);
}
static esp_err_t __esp_srp_srv_pubkey(esp_srp_handle_t *hd, char **bytes_B, int *len_B)
{
esp_mpi_t *k = calculate_k(hd);
esp_mpi_t *kv = NULL;
esp_mpi_t *gb = NULL;
if (!k) {
goto error;
}
hexdump_mpi("k", k);
hd->b = esp_mpi_new();
if (!hd->b) {
goto error;
}
esp_mpi_get_rand(hd->b, 256, -1, 0);
hexdump_mpi("b", hd->b);
/* B = kv + g^b */
kv = esp_mpi_new();
gb = esp_mpi_new();
hd->B = esp_mpi_new();
if (!kv || !gb || ! hd->B) {
goto error;
}
esp_mpi_a_mul_b_mod_c(kv, k, hd->v, hd->n, hd->ctx);
esp_mpi_a_exp_b_mod_c(gb, hd->g, hd->b, hd->n, hd->ctx);
esp_mpi_a_add_b_mod_c(hd->B, kv, gb, hd->n, hd->ctx);
hd->bytes_B = esp_mpi_to_bin(hd->B, len_B);
hd->len_B = *len_B;
*bytes_B = hd->bytes_B;
esp_mpi_free(k);
esp_mpi_free(kv);
esp_mpi_free(gb);
return ESP_OK;
error:
if (k) {
esp_mpi_free(k);
}
if (kv) {
esp_mpi_free(kv);
}
if (gb) {
esp_mpi_free(gb);
}
if (hd->B) {
esp_mpi_free(hd->B);
hd->B = NULL;
}
if (hd->b) {
esp_mpi_free(hd->b);
hd->b = NULL;
}
return ESP_FAIL;
}
static esp_err_t _esp_srp_gen_salt_verifier(esp_srp_handle_t *hd, const char *username, int username_len,
const char *pass, int pass_len, int salt_len)
{
/* Get Salt */
int str_salt_len;
esp_mpi_t *x = NULL;
hd->s = esp_mpi_new();
if (!hd->s) {
ESP_LOGE(TAG, "Failed to allocate bignum s");
goto error;
}
esp_mpi_get_rand(hd->s, 8 * salt_len, -1, 0);
hd->bytes_s = esp_mpi_to_bin(hd->s, &str_salt_len);
if (!hd->bytes_s) {
ESP_LOGE(TAG, "Failed to generate salt of len %d", salt_len);
goto error;
}
hd->len_s = salt_len;
ESP_LOGD(TAG, "Salt ->");
ESP_LOG_BUFFER_HEX_LEVEL(TAG, hd->bytes_s, str_salt_len, ESP_LOG_DEBUG);
/* Calculate X which is simply a hash for all these things */
x = calculate_x(hd->bytes_s, str_salt_len, username, username_len, pass, pass_len);
if (!x) {
ESP_LOGE(TAG, "Failed to calculate x");
goto error;
}
hexdump_mpi("x", x);
/* v = g^x % N */
hd->v = esp_mpi_new();
if (!hd->v) {
ESP_LOGE(TAG, "Failed to allocate bignum v");
goto error;
}
esp_mpi_a_exp_b_mod_c(hd->v, hd->g, x, hd->n, hd->ctx);
hexdump_mpi("Verifier", hd->v);
esp_mpi_free(x);
return ESP_OK;
error:
if (hd->s) {
esp_mpi_free(hd->s);
hd->s = NULL;
}
if (hd->bytes_s) {
free(hd->bytes_s);
hd->bytes_s = NULL;
hd->len_s = 0;
}
if (x) {
esp_mpi_free(x);
x = NULL;
}
if (hd->v) {
esp_mpi_free(hd->v);
hd->v = NULL;
}
return ESP_FAIL;
}
esp_err_t esp_srp_srv_pubkey(esp_srp_handle_t *hd, const char *username, int username_len,
const char *pass, int pass_len, int salt_len,
char **bytes_B, int *len_B, char **bytes_salt)
{
if (!hd || !username || !pass) {
return ESP_ERR_INVALID_ARG;
}
if (ESP_OK != _esp_srp_gen_salt_verifier(hd, username, username_len, pass, pass_len, salt_len)) {
goto error;
}
*bytes_salt = hd->bytes_s;
if (__esp_srp_srv_pubkey(hd, bytes_B, len_B) < 0 ) {
goto error;
}
return ESP_OK;
error:
if (hd->s) {
esp_mpi_free(hd->s);
hd->s = NULL;
}
if (*bytes_salt) {
free(*bytes_salt);
*bytes_salt = NULL;
hd->bytes_s = NULL;
hd->len_s = 0;
}
if (hd->v) {
esp_mpi_free(hd->v);
hd->v = NULL;
}
return ESP_FAIL;
}
esp_err_t esp_srp_srv_pubkey_from_salt_verifier(esp_srp_handle_t *hd, char **bytes_B, int *len_B)
{
if (!hd || !bytes_B || !len_B) {
return ESP_ERR_INVALID_ARG;
}
return __esp_srp_srv_pubkey(hd, bytes_B, len_B);
}
/* Generate salt-verifier pair for given username and password */
esp_err_t esp_srp_gen_salt_verifier(const char *username, int username_len,
const char *pass, int pass_len,
char **bytes_salt, int salt_len,
char **verifier, int *verifier_len)
{
esp_err_t ret = ESP_FAIL;
/* allocate and init temporary SRP handle */
esp_srp_handle_t *srp_hd = esp_srp_init(ESP_NG_3072);
if (!srp_hd) {
ESP_LOGE(TAG, "Failed to initialise security context!");
return ESP_ERR_NO_MEM;
}
// get salt and verifier
if (ESP_OK != _esp_srp_gen_salt_verifier(srp_hd, username, username_len, pass, pass_len, salt_len)) {
goto cleanup;
}
// convert to verifier bytes
*verifier = esp_mpi_to_bin(srp_hd->v, verifier_len);
if (!*verifier) {
ESP_LOGE(TAG, "Failed to allocate verifier bytes!");
ret = ESP_ERR_NO_MEM;
goto cleanup;
}
*bytes_salt = srp_hd->bytes_s;
srp_hd->bytes_s = NULL; // so that it won't be freed in `esp_srp_free` step
ret = ESP_OK;
cleanup:
esp_srp_free(srp_hd);
return ret;
}
esp_err_t esp_srp_set_salt_verifier(esp_srp_handle_t *hd, const char *salt, int salt_len,
const char *verifier, int verifier_len)
{
hd->bytes_s = malloc(salt_len);
if (!hd->bytes_s) {
goto error;
}
memcpy(hd->bytes_s, salt, salt_len);
hd->len_s = salt_len;
hd->s = esp_mpi_new_from_bin(salt, salt_len);
if (!hd->s) {
goto error;
}
hd->v = esp_mpi_new_from_bin(verifier, verifier_len);
if (!hd->v) {
goto error;
}
return ESP_OK;
error:
if (hd->bytes_s) {
free(hd->bytes_s);
hd->bytes_s = NULL;
hd->len_s = 0;
}
if (hd->s) {
esp_mpi_free(hd->s);
hd->s = NULL;
}
if (hd->v) {
esp_mpi_free(hd->v);
hd->v = NULL;
}
return ESP_FAIL;
}
esp_err_t esp_srp_get_session_key(esp_srp_handle_t *hd, char *bytes_A, int len_A, char **bytes_key, uint16_t *len_key)
{
esp_mpi_t *u = NULL;
esp_mpi_t *vu = NULL;
esp_mpi_t *avu = NULL;
esp_mpi_t *S = NULL;
char *bytes_S;
int len_S;
u = vu = avu = S = NULL;
bytes_S = NULL;
hd->bytes_A = malloc(len_A);
if (! hd->bytes_A) {
goto error;
}
memcpy(hd->bytes_A, bytes_A, len_A);
hd->len_A = len_A;
hd->A = esp_mpi_new_from_bin(bytes_A, len_A);
if (! hd->A) {
goto error;
}
u = calculate_u(hd, bytes_A, len_A);
if (! u) {
goto error;
}
hexdump_mpi("u", u);
/* S = (A v^u)^b */
vu = esp_mpi_new();
avu = esp_mpi_new();
S = esp_mpi_new();
if (!vu || !avu || !S ) {
goto error;
}
esp_mpi_a_exp_b_mod_c(vu, hd->v, u, hd->n, hd->ctx);
esp_mpi_a_mul_b_mod_c(avu, hd->A, vu, hd->n, hd->ctx);
esp_mpi_a_exp_b_mod_c(S, avu, hd->b, hd->n, hd->ctx);
hexdump_mpi("S", S);
bytes_S = esp_mpi_to_bin(S, &len_S);
hd->session_key = malloc(SHA512_HASH_SZ);
if (!hd->session_key || ! bytes_S) {
goto error;
}
mbedtls_sha512((unsigned char *)bytes_S, len_S, (unsigned char *)hd->session_key, 0);
*bytes_key = hd->session_key;
*len_key = SHA512_HASH_SZ;
free(bytes_S);
esp_mpi_free(vu);
esp_mpi_free(avu);
esp_mpi_free(S);
esp_mpi_free(u);
return ESP_OK;
error:
if (bytes_S) {
free(bytes_S);
}
if (vu) {
esp_mpi_free(vu);
}
if (avu) {
esp_mpi_free(avu);
}
if (S) {
esp_mpi_free(S);
}
if (u) {
esp_mpi_free(u);
}
if (hd->session_key) {
free(hd->session_key);
hd->session_key = NULL;
}
if (hd->A) {
esp_mpi_free(hd->A);
hd->A = NULL;
}
if (hd->bytes_A) {
free(hd->bytes_A);
hd->bytes_A = NULL;
}
return ESP_FAIL;
}
esp_err_t esp_srp_exchange_proofs(esp_srp_handle_t *hd, char *username, uint16_t username_len, char *bytes_user_proof, char *bytes_host_proof)
{
/* First calculate M */
unsigned char hash_n[SHA512_HASH_SZ];
unsigned char hash_g[SHA512_HASH_SZ];
unsigned char hash_n_xor_g[SHA512_HASH_SZ];
int i;
unsigned char hash_I[SHA512_HASH_SZ];
mbedtls_sha512((unsigned char *)username, username_len, (unsigned char *)hash_I, 0);
mbedtls_sha512((unsigned char *)hd->bytes_n, hd->len_n, (unsigned char *)hash_n, 0);
int pad_len = hd->len_n - hd->len_g;
char *s = calloc(pad_len, sizeof(char));
if (!s) {
return ESP_ERR_NO_MEM;
}
mbedtls_sha512_context ctx;
mbedtls_sha512_init(&ctx);
mbedtls_sha512_starts(&ctx, 0);
mbedtls_sha512_update(&ctx, (unsigned char *)s, pad_len);
mbedtls_sha512_update(&ctx, (unsigned char *)hd->bytes_g, hd->len_g);
mbedtls_sha512_finish(&ctx, hash_g);
mbedtls_sha512_free(&ctx);
for (i = 0; i < SHA512_HASH_SZ; i++) {
hash_n_xor_g[i] = hash_n[i] ^ hash_g[i];
}
unsigned char digest[SHA512_HASH_SZ];
mbedtls_sha512_init(&ctx);
mbedtls_sha512_starts(&ctx, 0);
mbedtls_sha512_update(&ctx, hash_n_xor_g, SHA512_HASH_SZ);
mbedtls_sha512_update(&ctx, hash_I, SHA512_HASH_SZ);
mbedtls_sha512_update(&ctx, (unsigned char *)hd->bytes_s, hd->len_s);
mbedtls_sha512_update(&ctx, (unsigned char *)hd->bytes_A, hd->len_A);
mbedtls_sha512_update(&ctx, (unsigned char *)hd->bytes_B, hd->len_B);
mbedtls_sha512_update(&ctx, (unsigned char *)hd->session_key, SHA512_HASH_SZ);
mbedtls_sha512_finish(&ctx, digest);
mbedtls_sha512_free(&ctx);
ESP_LOGD(TAG, "M ->");
ESP_LOG_BUFFER_HEX_LEVEL(TAG, (char *)digest, sizeof(digest), ESP_LOG_DEBUG);
if (memcmp(bytes_user_proof, digest, SHA512_HASH_SZ) != 0) {
free(s);
return ESP_FAIL;
}
/* M is now validated, let's proceed to H(AMK) */
mbedtls_sha512_init(&ctx);
mbedtls_sha512_starts(&ctx, 0);
mbedtls_sha512_update(&ctx, (unsigned char *)hd->bytes_A, hd->len_A);
mbedtls_sha512_update(&ctx, digest, SHA512_HASH_SZ);
mbedtls_sha512_update(&ctx, (unsigned char *)hd->session_key, SHA512_HASH_SZ);
mbedtls_sha512_finish(&ctx, (unsigned char *)bytes_host_proof);
mbedtls_sha512_free(&ctx);
ESP_LOGD(TAG, "AMK ->");
ESP_LOG_BUFFER_HEX_LEVEL(TAG, (char *)bytes_host_proof, SHA512_HASH_SZ, ESP_LOG_DEBUG);
if (s) {
free(s);
}
return ESP_OK;
}
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