check associate reply for consistency

Reject associate replies returning secret of inconsistent with association type
length.  This way severely broken OPs which return SHA1 association as SHA256
will still work in dumb mode.

Signed-off-by: Michael Krelin <hacker@klever.net>

1 files changed, 6 insertions, 3 deletions

diff --git a/lib/basic_rp.cc b/lib/basic_rp.cc
index 763a391..2da8416 100644
--- a/lib/basic_rp.cc
+++ b/lib/basic_rp.cc
@@ -10,25 +10,28 @@
 namespace opkele {
 
     static void dh_get_secret(
             secret_t& secret, const basic_openid_message& om,
             const char *exp_assoc, const char *exp_sess,
             util::dh_t& dh,
-            size_t d_len, unsigned char *(*d_fun)(const unsigned char*,size_t,unsigned char*) ) try {
+            size_t d_len, unsigned char *(*d_fun)(const unsigned char*,size_t,unsigned char*),
+            size_t exp_s_len) try {
         if(om.get_field("assoc_type")!=exp_assoc || om.get_field("session_type")!=exp_sess)
             throw bad_input(OPKELE_CP_ "Unexpected associate response");
         util::bignum_t s_pub = util::base64_to_bignum(om.get_field("dh_server_public"));
         vector<unsigned char> ck(DH_size(dh)+1);
         unsigned char *ckptr = &(ck.front())+1;
         int cklen = DH_compute_key(ckptr,s_pub,dh);
         if(cklen<0)
             throw exception_openssl(OPKELE_CP_ "failed to DH_compute_key()");
         if(cklen && (*ckptr)&0x80) {
             (*(--ckptr))=0; ++cklen; }
         unsigned char key_digest[d_len];
         secret.enxor_from_base64((*d_fun)(ckptr,cklen,key_digest),om.get_field("enc_mac_key"));
+        if(secret.size()!=exp_s_len)
+            throw bad_input(OPKELE_CP_ "Secret length isn't consistent with association type");
     }catch(opkele::failed_lookup& ofl) {
         throw bad_input(OPKELE_CP_ "Incoherent response from OP");
     } OPKELE_RETHROW
 
     static void direct_request(basic_openid_message& oum,const basic_openid_message& inm,const string& OP) {
         util::curl_pick_t curl = util::curl_pick_t::easy_init();
@@ -70,22 +73,22 @@ namespace opkele {
         secret_t secret;
         int expires_in;
         try {
             direct_request(res,req,OP);
             dh_get_secret( secret, res,
                     "HMAC-SHA256", "DH-SHA256",
-                    dh, SHA256_DIGEST_LENGTH, SHA256 );
+                    dh, SHA256_DIGEST_LENGTH, SHA256, SHA256_DIGEST_LENGTH );
             expires_in = util::string_to_long(res.get_field("expires_in"));
         }catch(exception& e) {
             try {
                 req.set_field("assoc_type","HMAC-SHA1");
                 req.set_field("session_type","DH-SHA1");
                 direct_request(res,req,OP);
                 dh_get_secret( secret, res,
                         "HMAC-SHA1", "DH-SHA1",
-                        dh, SHA_DIGEST_LENGTH, SHA1 );
+                        dh, SHA_DIGEST_LENGTH, SHA1, SHA_DIGEST_LENGTH );
                 expires_in = util::string_to_long(res.get_field("expires_in"));
             }catch(bad_input& e) {
                 throw dumb_RP(OPKELE_CP_ "OP failed to supply an association");
             }
         }
         return store_assoc(