This disclosure describes system on a chip (SOC) communications that prevent direct memory access (DMA) attacks. An example SoC includes an encryption engine and a security processor. The encryption engine is configured to encrypt raw input data using a cipher key to form an encrypted payload. The security processor is configured to select the cipher key from a key store holding a plurality of cipher keys based on a channel ID describing a {source subsystem, destination subsystem} tuple for the encrypted payload, to form an encryption header that includes the channel ID, to encapsulate the encrypted payload with the encryption header that includes the channel ID to form a crypto packet, and to transmit the crypto packet to a destination SoC that is external to the SoC.