Blind Signatures

Signatures made by a “blinded” signer.

• The signer cannot observe the contents it signs.

• Similar to a handwritten signature on an envelope containing a document and a carbon copy sheet.

Useful for ensuring the anonymity of the signed information holder, while the signed information provides some extra functionality.

• Signer $X$ knows who requires a signature $Y$.

• $X$signs $T_1$, but $Y$afterwards transforms it into a signature over $T_2$.

  • Not any $T_2$, a specific one linked to $T_1$.

• Requester $Y$ can present $T_2$ signed by $X$.

  • But it cannot change $T_2$.

  • $X$ cannot link $T_2$ to the $T_1$ that it observed when signing.