memcpy(chain + (cchain^blocksize), data, blocksize);
alg->decrypt.crypt(sch, data, data);
memxor(data, chain + cchain, blocksize);
cchain ^= blocksize;
memcpy(chain + (cchain^blocksize), data, blocksize);
alg->decrypt.crypt(sch, data, data);
memxor(data, chain + cchain, blocksize);
cchain ^= blocksize;