android - java.security.InvalidKeyException when implementing DH protocol -

in android application implement diffie-hellman protocol in order generate common secret between 2 users.

what following: when first user sends friendship request second one, app generates key pair, storing public 1 in remote database , private in local database.

here code first part:

generatekeys(); localdb.insertprivatekey(userid, entityid, privatekey); remotedb.insertfirstpublickey(userid, entityid, publickey); 

the generatekeys method following:

private void generatekeys() {         try {             final keypairgenerator keypairgenerator = keypairgenerator.getinstance("dh");             keypairgenerator.initialize(1024);              final keypair keypair = keypairgenerator.generatekeypair();              privatekey = keypair.getprivate();             publickey  = keypair.getpublic();         } catch (exception e) {             e.printstacktrace();         }     } 

when second user accepts request, key pair generated, once again storing private key in local db , public in remote. fetches public key of first user remote db, converts publickey , generate common secret.

here code second part:

generatekeys(); localdb.insertprivatekey(userid, entityid, privatekey); remotedb.insertsecondpublickey(entityid, userid, publickey); string stringfirstpubkey = remotedb.fetchfirstkey(entityid, userid); publickey firstpubkey = stringtopublickey(stringfirstpubkey); byte[] commonsecret = generatecommonsecret(firstpubkey); 

the stringtopublickey following:

private publickey stringtopublickey(string stringpubk) throws nosuchalgorithmexception, invalidkeyspecexception {     byte[] pubk = base64.decodebase64(stringpubk);     keyfactory keyfactory = keyfactory.getinstance("dh");     encodedkeyspec keyspec = new x509encodedkeyspec(pubk);     return keyfactory.generatepublic(keyspec); } 

and generatacommonsecret:

private byte[] generatecommonsecret(publickey firstpubkey) {     try {         final keyagreement keyagreement = keyagreement.getinstance("dh");         keyagreement.init(privatekey);         keyagreement.dophase(firstpubkey, true);         byte[] secretkey = adjustkeylenght(keyagreement.generatesecret());         return secretkey;     } catch (exception e) {         e.printstacktrace();     }      return null; } 

also when storing keys convert them string following:

string stringpubk = base64.encodebase64string(publickey.getencoded()); 

when executing following line in generatecommonsecret

keyagreement.dophase(firstpubkey, true); 

i exception

java.security.invalidkeyexception: dhpublickey not keyagreement!    @ com.android.org.bouncycastle.jcajce.provider.asymmetric.dh.keyagreementspi.enginedophase(keyagreementspi.java:101) @ javax.crypto.keyagreement.dophase(keyagreement.java:383) 

can me finding problem? weird if try in single java class, without storing , retrieving keys, works fine.