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
@@ -12,9 +12,10 @@ 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);
@@ -25,8 +26,10 @@ namespace opkele {
 	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
 
@@ -72,18 +75,18 @@ namespace opkele {
 	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");
 	    }