Message Authentication Code or MAC, is a well-studied cryptographic primitive
that is used in order to authenticate communication between two parties sharing
a secret key. A Tokenized MAC or TMAC is a related cryptographic primitive,
introduced by Ben-David & Sattath (QCrypt’17) which allows to delegate limited
signing authority to third parties via the use of single-use quantum signing
tokens. These tokens can be issued using the secret key, such that each token
can be used to sign at most one document.
We provide an elementary construction for TMAC based on BB84 states. Our
construction can tolerate up to 14% noise, making it the first noise-tolerant
TMAC construction. The simplicity of the quantum states required for our
construction combined with the noise-tolerance, makes it practically more
feasible than the previous TMAC construction.
The TMAC is existentially unforgeable against adversaries with signing and
verification oracles (i.e., analogous to EUF-CMA security for MAC), assuming
post-quantum collision-resistant hash functions exist.