Examples relate to Input/Output (I/O) data encryption and decryption. In an example, an encryption/decryption engine on an Integrated Circuit (IC) of a computing device obtains at least one plaintext data. Some examples determine, by the encryption/decryption engine, whether the at least one plaintext data is to be sent to a memory in the computing device or to an I/O device. Some examples apply, when the at least one plaintext data is to be sent to the I/O device and by the encryption/decryption engine, an encryption primitive of a block cipher encryption algorithm to the at least one plaintext data to create output encrypted data, wherein an initialization vector that comprises a random number is applied to the encryption primitive.