Content Extraction Signatures

Motivated by emerging needs in online interactions, we define a new type of digital signature called a ‘Content Extraction Signature’ (CES). A CES allows the owner, Bob, of a document signed by Alice, to produce an ‘extracted signature’ on selected extracted portions of the original document, which can be verified (to originate from Alice) by any third party Cathy, without knowledge of the unextracted (removed) document portions. The new signature therefore achieves verifiable content extraction with minimal multi-party interaction. We specify desirable functional and security requirements from a CES (including an efficiency requirement: a CES should be more efficient in either computation or communication than the simple multiple signature solution). We propose and analyse four provably secure CES constructions which satisfy our requirements, and evaluate their performance characteristics.