Digital Signature

Digital Signatures are fundamental in authentication and non-repudiation.

• $\mathcal{M}$ is a set of messages that can be signed
• $\mathcal{S}$ is a set of elements called signatures, e.g. $n$-bit strings
• $S_A:\mathcal{M}\to \mathcal{S}$, is a signing transformation for entity $A$, and kept secret by $A$.
• $V_A:\mathcal{M}\times \mathcal{S}\to \{\text{true},\text{false}\}$ is a verification transformation for $A$‘s signature and is publicly known.

$S_A$ and $V_A$ provide a digital signature scheme for $A$.