Covert Channels in Redactable Blockchain

Redactable blockchains allow the modification of a block through an editor without changing the value of the block’s original hash value. This is achieved by using Chameleon hash functions. We investigate the possibility of hiding a secret message in a redactable blockchain via finding a collision in the random value used in Chameleon hash functions. We demonstrate that some constructions allow efficient computation of such collision, i.e., allow creation of a covert channel or storage.