Redaction breaks digital signatures. How to redact and still prove the rest is the original - Cogito

Remove one word from a signed document and the signature fails. That has been true since digital signatures were invented. Cogito Group built a proof of concept that breaks the rule. Sign the document first, redact it afterwards, and the original signature still verifies. Anyone receiving the file can prove two things at once: who published it, and that nothing except the redactions changed. An Australian Government department brought Cogito the problem. It needed to release documents publicly with parts removed, and it needed recipients to be able to check that the rest was untouched. Aiden Rogers, a DevOps engineer at Cogito Group, walks through the problem, the cryptography underneath it, and a live demonstration of the working prototype. Covered in this session: Why re-signing after redaction proves less than people assume. A conventional signature is created after the edit, so it attests only to the redacted copy. A word quietly altered looks exactly like a word legitimately removed. How a Merkle tree makes selective redaction survivable. Every word is salted and hashed, pairs are hashed upward to a single root, and that root is signed. Redaction deletes the word and its salt but keeps its hash, so the verifier can rebuild the same root from what remains. AI-assisted redaction with a human in the loop. Plain-English prompts such as "redact all IP addresses", with an operator reviewing everything before signing. Verification without a connection. Everything needed to check the document sits inside the PDF, so it works in air-gapped environments and needs no call back to Cogito. Built on ISO/IEC 23264-2:2024 for redactable signatures, ML-DSA-87 for the signature, and SHA-512 for the tree. ML-DSA-87 is the highest NIST post-quantum parameter set, chosen so released documents stay provably authentic for decades. Audience questions cover hybrid classical and post-quantum signing, X.509 storage of post-quantum keys, and exactly how the Merkle tree is rebuilt from a redacted file. Cogito Group is an Australian-owned cyber security company founded in Canberra in 2011. Its platform, Jellyfish, manages identities, certificates, credentials and cryptographic keys together, and more than 5,000 business and government entities use it for authentication, digital signing and credential management. The Jellyfish Certificate Authority is Common Criteria certified and NIAP listed. The PKI is Gatekeeper certified. If you have questions about applying this please email sales@cogitogroup.net More on Cogito Group: www.cogitogroup.net 0:00 Welcome, and who Cogito Group are 1:40 The government department's problem, and why it was unsolvable 2:26 What was built, and the standards behind it 3:34 Where redaction destroys provenance: FOI, court extracts, health records 4:29 Forgery is free, citizens cannot check, and redactions leak 5:47 Interoperable, quantum-safe, and verifiable with no connection 7:34 What the project had to deliver 8:49 Why re-signing after redaction proves less than you think 9:47 What a Merkle tree is, in ninety seconds 10:26 Tokenise, sign the root, redact, rebuild 11:07 Live demo: redact, AI assist, sign, then try to Ctrl+F it 13:53 Speed, memory, and the file size trade-off 14:37 Roadmap: myID, SharePoint, email, images and video 17:19 What was built, and what it proves 18:31 Q&A: does file growth hurt an agency publishing at scale? 20:04 Q&A: how is this post-quantum ready? 20:54 Q&A: what do I do to check a document I receive? 22:17 Q&A: hybrid classical and post-quantum signing, and X.509 key storage 23:37 Q&A: why build quantum-safe into tools now 24:34 Q&A: rebuilding the Merkle tree from a redacted file 26:11 Next steps, and where this fits