Re: SymmetricCipher Decoder is not working if created dynamically.

[Cornel Maftuleac]

Rickey Braddam wrote: Hi, Cornell. I think I see what's happening here, but if I'm right I don't know why the decrypt works in either case.... at any rate, my comments are embedded below. I've snipped the original that my comments don't apply to. int main(int argc, char* argv[]) { UCHAR plain[] = "test message"; UCHAR out_plain[sizeof(plain)]; UCHAR chiper[sizeof(plain)]; UCHAR chiper2[sizeof(plain)]; UCHAR key[DES::DEFAULT_KEYLENGTH]; UCHAR iv[DES::BLOCKSIZE]; unsigned bSize = strlen((char*)plain); srand(time(0)); for(int i=0;i<DES::DEFAULT_KEYLENGTH;i++) key[i] = rand()%256; for(i=0;i<DES::BLOCKSIZE;i++) iv[i] = rand()%256; Above is the first place I see a potential problem. You aren't saving a copy of the IV for decryption use. Note that the IV is updated with every block encrypted, changing it from its original value. I suggest you do this: UCHAR ivDec[DES::BLOCKSIZE]; for(i=0;i<DES::BLOCKSIZE;i++) ivDec[i] = iv[i]; Then use ivDec to construct the decryption object. You'll need the original IV anyway to send to the recipient or they won't be able to decrypt the ciphertext. { //THIS PART RUN'S FINE!!! DES::Encryption desEncryption(key, DES::DEFAULT_KEYLENGTH); CFB_Mode_ExternalCipher::Encryption cfbEncryption(desEncryption, iv); DES::Encryption desDecryption(key, DES::DEFAULT_KEYLENGTH); CFB_Mode_ExternalCipher::Decryption cfbDecryption(desDecryption, iv); I think I see it. You're declaring desDecryption as a DES::Encryption object here, which is correct for CFB, OFB, and CTR modes. cfbEncryption.ProcessData(chiper, plain,bSize); cfbDecryption.ProcessData(out_plain, chiper,bSize); } { //THIS PART DOES NOT WORK!!! //even if it should be the same as previous... //encrypt work's ok the chiper and chiper2 is equal, but the out_plain is different! DES::Encryption *chpEnc = new DES::Encryption(key, DES::DEFAULT_KEYLENGTH); CFB_Mode_ExternalCipher::Encryption *cfbEncrypt = new CFB_Mode_ExternalCipher::Encryption(*chpEnc, iv); /******************************************************************************/ DES::Decryption *chpDec = new DES::Decryption(key, DES::DEFAULT_KEYLENGTH); CFB_Mode_ExternalCipher::Decryption *cfbDecrypt = new CFB_Mode_ExternalCipher::Decryption(*chpDec, iv); /*******************************************************************************/ Looks like the block above is your problem. *chpDec MUST be an encryption object for CFB, OFB, and CTR modes. In the code that works above, you use "DES::Encryption desDecryption" to construct the decrypter. Here you are using "DES::Decryption *chpDec" to construct it. Change that to "DES::Encryption *chpDec" and it should work. cfbEncrypt->ProcessData(chiper2, plain, bSize); cfbDecrypt->ProcessData(out_plain, chiper2, bSize); delete cfbEncrypt; delete cfbDecrypt; delete chpEnc; delete chpDec; } I hope this turns out to be the solution, but if not, at least I tried. Rickey Yes, this worked! Thanks! :) About the IV i have checked it is not changing, but I will note this for future. But I still not understand, when I am doing:         DES::Decryption desEncryption(key, DES::DEFAULT_KEYLENGTH);         CFB_Mode_ExternalCipher::Encryption cfbEncryption(desEncryption, iv);                 DES::Decryption desDecryption(key, DES::DEFAULT_KEYLENGTH);         CFB_Mode_ExternalCipher::Decryption cfbDecryption(desDecryption, iv);                 cfbEncryption.ProcessData(chiper, plain,bSize);         cfbDecryption.ProcessData(out_plain, chiper,bSize); it works, when:         DES::Encryption desEncryption(key, DES::DEFAULT_KEYLENGTH);         CFB_Mode_ExternalCipher::Encryption cfbEncryption(desEncryption, iv);                 DES::Encryption desDecryption(key, DES::DEFAULT_KEYLENGTH);         CFB_Mode_ExternalCipher::Decryption cfbDecryption(desDecryption, iv);                 cfbEncryption.ProcessData(chiper, plain,bSize);         cfbDecryption.ProcessData(out_plain, chiper,bSize); it allso works, but the chipertext itself is different... Which one to use and is this the right way of  doing encryption/decription? What is the difference beetween DES::Encryption and DES::Decryption if  they both works...