refining changeset 4483 by introducing charon.dh_exponent_ansi_x9_42 key

[strongswan.git] / src / libstrongswan / plugins / gmp / gmp_diffie_hellman.c

diff --git a/src/libstrongswan/plugins/gmp/gmp_diffie_hellman.c b/src/libstrongswan/plugins/gmp/gmp_diffie_hellman.c
index b811026..0f90314 100644 (file)
--- a/src/libstrongswan/plugins/gmp/gmp_diffie_hellman.c
+++ b/src/libstrongswan/plugins/gmp/gmp_diffie_hellman.c
@@ -304,23 +304,28 @@ struct modulus_entry_t {
        size_t modulus_len;
        
        /* 
+        * Optimum length of exponent in bytes.
+        */     
+       size_t opt_exponent_len;
+
+       /* 
         * Generator value.
         */     
        u_int16_t generator;
 };
 
 /**
- * All supported modulus values.
+ * All supported modulus values - optimum exponent size according to RFC 3526.
  */
 static modulus_entry_t modulus_entries[] = {
-       {MODP_768_BIT, group1_modulus, sizeof(group1_modulus), 2},
-       {MODP_1024_BIT, group2_modulus, sizeof(group2_modulus), 2},
-       {MODP_1536_BIT, group5_modulus, sizeof(group5_modulus), 2},
-       {MODP_2048_BIT, group14_modulus, sizeof(group14_modulus), 2},
-       {MODP_3072_BIT, group15_modulus, sizeof(group15_modulus), 2},
-       {MODP_4096_BIT, group16_modulus, sizeof(group16_modulus), 2},
-       {MODP_6144_BIT, group17_modulus, sizeof(group17_modulus), 2},
-       {MODP_8192_BIT, group18_modulus, sizeof(group18_modulus), 2},
+       {MODP_768_BIT,  group1_modulus,  sizeof(group1_modulus),  32, 2},
+       {MODP_1024_BIT, group2_modulus,  sizeof(group2_modulus),  32, 2},
+       {MODP_1536_BIT, group5_modulus,  sizeof(group5_modulus),  32, 2},
+       {MODP_2048_BIT, group14_modulus, sizeof(group14_modulus), 48, 2},
+       {MODP_3072_BIT, group15_modulus, sizeof(group15_modulus), 48, 2},
+       {MODP_4096_BIT, group16_modulus, sizeof(group16_modulus), 64, 2},
+       {MODP_6144_BIT, group17_modulus, sizeof(group17_modulus), 64, 2},
+       {MODP_8192_BIT, group18_modulus, sizeof(group18_modulus), 64, 2},
 };
 
 typedef struct private_gmp_diffie_hellman_t private_gmp_diffie_hellman_t;
@@ -375,6 +380,11 @@ struct private_gmp_diffie_hellman_t {
        size_t p_len;
        
        /**
+        * Optimal exponent length.
+        */
+       size_t opt_exponent_len;
+
+       /**
         * True if shared secret is computed and stored in my_public_value.
         */
        bool computed;
@@ -504,6 +514,7 @@ static status_t set_modulus(private_gmp_diffie_hellman_t *this)
                        chunk.len = modulus_entries[i].modulus_len;
                        mpz_import(this->p, chunk.len, 1, 1, 1, 0, chunk.ptr);
                        this->p_len = chunk.len;
+                       this->opt_exponent_len = modulus_entries[i].opt_exponent_len;
                        mpz_set_ui(this->g, modulus_entries[i].generator);
                        status = SUCCESS;
                        break;
@@ -534,6 +545,8 @@ gmp_diffie_hellman_t *gmp_diffie_hellman_create(diffie_hellman_group_t group)
        private_gmp_diffie_hellman_t *this = malloc_thing(private_gmp_diffie_hellman_t);
        rng_t *rng;
        chunk_t random;
+       bool ansi_x9_42;
+       size_t exponent_len;
 
        /* public functions */
        this->public.dh.get_shared_secret = (status_t (*)(diffie_hellman_t *, chunk_t *)) get_shared_secret;
@@ -567,11 +580,22 @@ gmp_diffie_hellman_t *gmp_diffie_hellman_create(diffie_hellman_group_t group)
                destroy(this);
                return NULL;
        }
-       rng->allocate_bytes(rng, DH_EXPONENT_ENTROPY_SIZE / BITS_PER_BYTE, &random);
+
+       ansi_x9_42 = lib->settings->get_int(lib->settings,
+                                        "charon.dh_exponent_ansi_x9_42", TRUE);
+       exponent_len = (ansi_x9_42) ? this->p_len : this->opt_exponent_len;     
+       rng->allocate_bytes(rng, exponent_len, &random);
        rng->destroy(rng);
+
+       if (ansi_x9_42)
+       {
+               /* achieve bitsof(p)-1 by setting MSB to 0 */
+               *random.ptr &= 0x7F;
+       }
        mpz_import(this->xa, random.len, 1, 1, 1, 0, random.ptr);
        chunk_free(&random);
-       
+       DBG2("size of DH secret exponent: %u bits", mpz_sizeinbase(this->xa, 2));
+
        mpz_powm(this->ya, this->g, this->xa, this->p);
        
        return &this->public;