static createCipher(cryptoScheme, dataKey, offset, log, cb) {
        /* aes-256-ctr decipher is both ways */
        this.createDecipher(cryptoScheme, dataKey, offset, log, cb);
    }
createCipher (currently same as createDecipher function above.  this
wrapper is included to preserve flexibility)
@param {number} cryptoScheme - cryptoScheme being used
@param {buffer} dataKey - the unencrypted key (either from the
appliance on a get or originally generated by kms in the case of a put)
@param {number} offset - offset
@param {object} log - logger object
@param {function} cb - cb from external call
@returns {undefined}
@callback called with (err, cipher: ReadWritable.stream)