dh-gex: Add support for moduli file parsing
Signed-off-by: Aris Adamantiadis <aris@0xbadc0de.be> Reviewed-by: Jakub Jelen <jjelen@redhat.com> Reviewed-by: Andreas Schneider <asn@cryptomilk.org>
Этот коммит содержится в:
Aris Adamantiadis
Andreas Schneider
родитель
31da8025b2
Коммит
b36219369d
252
src/dh-gex.c
252
src/dh-gex.c
@ -23,6 +23,11 @@
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#include "config.h"
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#include <errno.h>
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#include <stdbool.h>
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#include <string.h>
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#include <stdio.h>
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#include "libssh/priv.h"
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#include "libssh/dh-gex.h"
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#include "libssh/libssh.h"
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@ -252,3 +257,250 @@ error:
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return SSH_PACKET_USED;
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}
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#ifdef WITH_SERVER
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#define MODULI_FILE "/etc/ssh/moduli"
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/* 2 "Safe" prime; (p-1)/2 is also prime. */
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#define SAFE_PRIME 2
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/* 0x04 Probabilistic Miller-Rabin primality tests. */
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#define PRIM_TEST_REQUIRED 0x04
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/**
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* @internal
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*
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* @brief Determines if the proposed modulus size is more appropriate than the
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* current one.
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*
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* @returns 1 if it's more appropriate. Returns 0 if same or less appropriate
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*/
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static bool dhgroup_better_size(uint32_t pmin,
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uint32_t pn,
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uint32_t pmax,
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size_t current_size,
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size_t proposed_size)
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{
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if (current_size == proposed_size) {
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return false;
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}
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if (current_size == pn) {
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/* can't do better */
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return false;
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}
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if (current_size == 0 && proposed_size >= pmin && proposed_size <= pmax) {
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return true;
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}
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if (proposed_size < pmin || proposed_size > pmax) {
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/* out of bounds */
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return false;
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}
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if (current_size == 0) {
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/* not in the allowed window */
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return false;
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}
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if (proposed_size >= pn && proposed_size < current_size) {
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return true;
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}
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if (proposed_size <= pn && proposed_size > current_size) {
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return true;
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}
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if (proposed_size >= pn && current_size < pn) {
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return true;
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}
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/* We're in the allowed window but a better match already exists. */
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return false;
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}
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/** @internal
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* @brief returns 1 with 1/n probability
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* @returns 1 on with P(1/n), 0 with P(n-1/n).
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*/
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static bool invn_chance(int n)
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{
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uint32_t nounce;
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ssh_get_random(&nounce, sizeof(nounce), 0);
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return (nounce % n) == 0;
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}
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/** @internal
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* @brief retrieves a DH group from an open moduli file.
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*/
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static int ssh_retrieve_dhgroup_file(FILE *moduli,
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uint32_t pmin,
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uint32_t pn,
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uint32_t pmax,
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size_t *best_size,
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char **best_generator,
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char **best_modulus)
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{
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char timestamp[32] = {0};
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char generator[32] = {0};
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char modulus[4096] = {0};
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size_t type, tests, tries, size, proposed_size;
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int firstbyte;
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int rc;
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size_t line = 0;
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size_t best_nlines = 0;
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for(;;) {
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line++;
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firstbyte = getc(moduli);
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if (firstbyte == '#'){
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do {
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firstbyte = getc(moduli);
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} while(firstbyte != '\n' && firstbyte != EOF);
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continue;
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}
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if (firstbyte == EOF) {
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break;
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}
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ungetc(firstbyte, moduli);
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rc = fscanf(moduli,
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"%31s %zu %zu %zu %zu %31s %4095s\n",
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timestamp,
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&type,
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&tests,
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&tries,
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&size,
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generator,
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modulus);
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if (rc != 7){
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if (rc == EOF) {
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break;
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}
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SSH_LOG(SSH_LOG_INFO, "Invalid moduli entry line %zu", line);
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do {
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firstbyte = getc(moduli);
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} while(firstbyte != '\n' && firstbyte != EOF);
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continue;
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}
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/* we only want safe primes that were tested */
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if (type != SAFE_PRIME || !(tests & PRIM_TEST_REQUIRED)) {
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continue;
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}
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proposed_size = size + 1;
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if (proposed_size != *best_size &&
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dhgroup_better_size(pmin, pn, pmax, *best_size, proposed_size)) {
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best_nlines = 0;
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*best_size = proposed_size;
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}
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if (proposed_size == *best_size) {
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best_nlines++;
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}
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/* Use reservoir sampling algorithm */
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if (proposed_size == *best_size && invn_chance(best_nlines)) {
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SAFE_FREE(*best_generator);
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SAFE_FREE(*best_modulus);
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*best_generator = strdup(generator);
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if (*best_generator == NULL) {
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return SSH_ERROR;
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}
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*best_modulus = strdup(modulus);
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if (*best_modulus == NULL) {
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SAFE_FREE(*best_generator);
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return SSH_ERROR;
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}
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}
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}
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if (*best_size != 0) {
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SSH_LOG(SSH_LOG_INFO,
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"Selected %zu bits modulus out of %zu candidates in %zu lines",
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*best_size,
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best_nlines - 1,
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line);
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} else {
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SSH_LOG(SSH_LOG_WARNING,
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"No moduli found for [%u:%u:%u]",
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pmin,
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pn,
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pmax);
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}
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return SSH_OK;
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}
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/** @internal
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* @brief retrieves a DH group from the moduli file based on bits len parameters
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* @param[in] pmin minimum group size in bits
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* @param[in] pn preferred group size
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* @param[in] pmax maximum group size
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* @param[out] size size of the chosen modulus
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* @param[out] p modulus
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* @param[out] g generator
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* @return SSH_OK on success, SSH_ERROR otherwise.
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*/
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/* TODO Make this function static when only used in this file */
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int ssh_retrieve_dhgroup(uint32_t pmin,
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uint32_t pn,
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uint32_t pmax,
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size_t *size,
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bignum *p,
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bignum *g);
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int ssh_retrieve_dhgroup(uint32_t pmin,
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uint32_t pn,
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uint32_t pmax,
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size_t *size,
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bignum *p,
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bignum *g)
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{
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FILE *moduli = NULL;
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char *generator = NULL;
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char *modulus = NULL;
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int rc;
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moduli = fopen(MODULI_FILE, "r");
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if (moduli == NULL) {
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SSH_LOG(SSH_LOG_WARNING,
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"Unable to open moduli file: %s",
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strerror(errno));
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return SSH_ERROR;
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}
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*size = 0;
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*p = NULL;
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*g = NULL;
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rc = ssh_retrieve_dhgroup_file(moduli,
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pmin,
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pn,
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pmax,
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size,
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&generator,
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&modulus);
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if (rc == SSH_ERROR || *size == 0) {
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goto error;
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}
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rc = bignum_hex2bn(generator, g);
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if (rc == 0) {
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goto error;
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}
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rc = bignum_hex2bn(modulus, p);
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if (rc == 0) {
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goto error;
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}
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SAFE_FREE(generator);
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SAFE_FREE(modulus);
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return SSH_OK;
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error:
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bignum_safe_free(*g);
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bignum_safe_free(*p);
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SAFE_FREE(generator);
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SAFE_FREE(modulus);
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return SSH_ERROR;
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}
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#endif /* WITH_SERVER */
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