Perhaps you misinterpreted my reply. I didn’t intend to dispute parent’s claim, merely to correct a mechanical detail. Git signatures are more or less only as

Perhaps you misinterpreted my reply. I didn’t intend to dispute parent’s claim, merely to correct a mechanical detail. Git signatures are more or less only as secure as SHA-1, although the properties it relies on are not yet compromised and several factors mitigate the real-world risk. A practical preimage attack on SHA-1 would seriously undermine the security of git signatures since the string being signed includes two or more SHA-1 hashes representing a content snapshot and the commit ancestry. Arbitrary preimage attacks would make it possible to modify a repo’s contents or history without invalidating oids or signatures. In practice only collision attacks have been found, all of which have a detectable signature that git has been modified to detect. Disclosure: I work at GitHub, but am speaking for myself.