Methods, apparatus and computer readable media for transferring encrypted and unencrypted data between processing devices are disclosed. Example data transmission methods disclosed herein include dividing, at a first processing device, a set of data collected at the first processing device into a first unencrypted data subset and a second unencrypted data subset. Disclosed example methods also include encrypting, at the first processing device, the first unencrypted data subset using an encryption key provided by a second processing device to generate a first encrypted data subset. Disclosed example methods further include transmitting the second unencrypted data subset from the first processing device to the second processing device before transmitting the first encrypted data subset from the first processing device to the second processing device to thereby transmit the set of data from the first processing device to the second processing device.