Some examples described herein provide for securely booting a heterogeneous integration circuitry apparatus. In an example, an apparatus (e.g., heterogeneous integration circuitry) includes a first portion and a second portion of one or more entropy sources on a first component and a second component, respectively. The apparatus also includes a key generation circuit communicatively coupled with the first portion and the second portion to generate a key encrypted key based on a first set of bits output by the first portion and a second set of bits output by the second portion. The apparatus also includes a key security circuit to generate, based on the key encrypted key and an encrypted public key stored at the apparatus, a plaintext public key to be used by a boot loader during a secure booting operation for the apparatus.