How big is a ProofMark?

A ProofMark is a very small data object comprised of a timestamp, a serial number, a time interval identifier, a digest of the data concerned, a digest of the last document proofmarked… all hashed and encrypted with the appropriate interval’s private key. The public key associated with the time interval that created the ProofMark is also appended. The size of the ProofMark (without the public key) will depend on the hashing algorithm and the encryption key size. For example, if a SHA1 is used the encrypted digest will be 20 bytes long. If SHA256 is used, the size increases to 32 bytes.