  An ideal signature material and method, which can be used to prove the
authenticity of a physical item and against forgery, should be immune to the
fast developments in digital and engineering technologies. Herein, the design
of signature material combining cryptographic hash function and DNA
steganography is proposed. The encrypting materials are used to construct a
series of time-stamped records (blockchain) associated with published hash
values, while each DNA-encrypted block is associated with a set of DNA keys.
The decrypted DNA information, as digital keys, can be validated through a hash
function to compare with the published hash values. The blocks can also be
cross-referenced among different related signatures. While both digital
cryptography and DNA steganography can have large key size, automated brutal
force search is far more labor intensive and expensive for DNA steganography
with wet lab experiments, as compared to its digital counterpart. Moreover, the
time-stamped blockchain structure permits the incorporation of new
cryptographic functions and DNA steganographies over time, thus can evolve over
time without losing the continuous history line.
