cryptography - 3DES key exchange with RSA in Java -

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i'm implementing webservice in java in server needs send 3des key client using rsa algorithm. symmetric generated server. both server , client have own rsa key-pairs, exchanged.

in code, server sends symmetric key client.

@webmethod public byte[] getsymmetrickey(){     try{         cipher cipher = cipher.getinstance("rsa");          // first, encrypts symmetric key client's public key         cipher.init(cipher.encrypt_mode, this.clientkey);         byte[] partialcipher = cipher.dofinal(this.key.getbytes());          // finally, encrypts previous result server's private key         cipher.init(cipher.encrypt_mode, this.privatekey);         byte[] cipherdata = cipher.dofinal(partialcipher);          return cipherdata;     }catch (exception ex){         ex.printstacktrace();     }  }

when run encryption server's private key, error of illegalblocksizeexception. why exception if padding activated default? i've tried explicitly activate padding cipher.getinstance("rsa/ecb/pkcs1padding"). finally, here's exception output:

    severe: javax.crypto.illegalblocksizeexception: data must not longer 245 bytes javax.crypto.illegalblocksizeexception: data must not longer 245 bytes     @ com.sun.crypto.provider.rsacipher.dofinal(rsacipher.java:346)     @ com.sun.crypto.provider.rsacipher.enginedofinal(rsacipher.java:391)     @ javax.crypto.cipher.dofinal(cipher.java:2087)     @ server.filetransfererimpl.getsymmetrickey(filetransfererimpl.java:112)     @ sun.reflect.nativemethodaccessorimpl.invoke0(native method)     @ sun.reflect.nativemethodaccessorimpl.invoke(unknown source)     @ sun.reflect.delegatingmethodaccessorimpl.invoke(unknown source)     @ java.lang.reflect.method.invoke(unknown source)     @ sun.reflect.misc.trampoline.invoke(unknown source)     @ sun.reflect.nativemethodaccessorimpl.invoke0(native method)     @ sun.reflect.nativemethodaccessorimpl.invoke(unknown source)     @ sun.reflect.delegatingmethodaccessorimpl.invoke(unknown source)     @ java.lang.reflect.method.invoke(unknown source)     @ sun.reflect.misc.methodutil.invoke(unknown source)     @ sun.reflect.nativemethodaccessorimpl.invoke0(native method)     @ sun.reflect.nativemethodaccessorimpl.invoke(unknown source)     @ sun.reflect.delegatingmethodaccessorimpl.invoke(unknown source)     @ java.lang.reflect.method.invoke(unknown source)     @ com.sun.xml.internal.ws.api.server.methodutil.invoke(unknown source)     @ com.sun.xml.internal.ws.api.server.instanceresolver$1.invoke(unknown source)     @ com.sun.xml.internal.ws.server.invokertube$2.invoke(unknown source)     @ com.sun.xml.internal.ws.server.sei.endpointmethodhandler.invoke(unknown source)     @ com.sun.xml.internal.ws.server.sei.seiinvokertube.processrequest(unknown source)     @ com.sun.xml.internal.ws.api.pipe.fiber.__dorun(unknown source)     @ com.sun.xml.internal.ws.api.pipe.fiber._dorun(unknown source)     @ com.sun.xml.internal.ws.api.pipe.fiber.dorun(unknown source)     @ com.sun.xml.internal.ws.api.pipe.fiber.runsync(unknown source)     @ com.sun.xml.internal.ws.server.wsendpointimpl$2.process(unknown source)     @ com.sun.xml.internal.ws.transport.http.httpadapter$httptoolkit.handle(unknown source)     @ com.sun.xml.internal.ws.transport.http.httpadapter.handle(unknown source)     @ com.sun.xml.internal.ws.transport.http.server.wshttphandler.handleexchange(unknown source)     @ com.sun.xml.internal.ws.transport.http.server.wshttphandler.handle(unknown source)     @ com.sun.net.httpserver.filter$chain.dofilter(unknown source)     @ sun.net.httpserver.authfilter.dofilter(unknown source)     @ com.sun.net.httpserver.filter$chain.dofilter(unknown source)     @ sun.net.httpserver.serverimpl$exchange$linkhandler.handle(unknown source)     @ com.sun.net.httpserver.filter$chain.dofilter(unknown source)     @ sun.net.httpserver.serverimpl$exchange.run(unknown source)     @ java.util.concurrent.threadpoolexecutor.runworker(unknown source)     @ java.util.concurrent.threadpoolexecutor$worker.run(unknown source)     @ java.lang.thread.run(unknown source)

i researching soem stuff today , found question. since has not been answered, i'll leave here future reference.

according pkcs #1, rsaes-pkcs1-v1_5-encrypt algorithm can encrypt k - 11 bytes k "size" of key in bytes. 11 bytes used "headers".

if using 2048 bits rsa key, gives k = 256 , can encrypt 256 - 11 = 245 bytes of data.

check actual size of this.key.


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