  Signature schemes, proposed in 1976 by Diffie and Hellman, have become
ubiquitous across modern communications. They allow for the exchange of
messages from one sender to multiple recipients, with the guarantees that
messages cannot be forged or tampered with and that messages also can be
forwarded from one recipient to another without compromising their validity.
Signatures are different from, but no less important than encryption, which
ensures the privacy of a message. Commonly used signature protocols -
signatures based on the Rivest-Adleman-Shamir (RSA) algorithm, the digital
signature algorithm (DSA), and the elliptic curve digital signature algorithm
(ECDSA) - are only computationally secure, similar to public key encryption
methods. In fact, since these rely on the difficulty of finding discrete
logarithms or factoring large primes, it is known that they will become
completely insecure with the emergence of quantum computers. We may therefore
see a shift towards signature protocols that will remain secure even in a
post-quantum world. Ideally, such schemes would provide unconditional or
information-theoretic security. In this paper, we aim to provide an accessible
and comprehensive review of existing unconditionally secure signature schemes
for signing classical messages, with a focus on unconditionally secure quantum
signature schemes.
